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This thesis is divided into three parts with the main goal allocating novel antimicrobial compounds that could be used as future antibiotics. The first part aimed to evaluate the potential of plant suspension cultures for the production of antimicrobial proteins. The extracellular, intracellular and cell wall bound fractions of seven heterotrophic and photomixotrophic plant cell suspension cultures treated with nine different elicitors were tested for the elicitor dependent production of antimicrobial proteins. Bioactivities were tested against a selected panel of human isolates including Gram-positive and Gram-negative bacteria as well as fungi using the disc diffusion assay. The intracellular fractions of elicited cell cultures were more active than extracellular fractions while the cell wall bound fractions showed lowest activities. Among the 21 fractions tested, the intracellular fraction of Lavendula angustifolia elicited with DC3000 was most active against Candida maltosa. The second most active fraction was the intracellular fraction of Arabidopsis thaliana elicited with salicylic acid which was moreover active against all test strains. The antimicrobial activity of elicited Arabidopsis thaliana cell cultures was tested by bioautography to locate the antimicrobial proteins in the crude extract. The intracellular fraction of photomixotrophic Arabidopsis thaliana cells elicited with salicylic acid was selected for further gel filtration chromatography on S-200 column leading to the purification of one 19 kDa antimicrobially active protein, designated, AtAMP. Our findings suggest that elicited plant cell cultures may present a new promising alternative source of antimicrobial proteins. The second part comprises the isolation of actinomycetes associated with marine sponges and testing the bioactivities of new species for further investigations. Actinobacterial communities of eleven taxonomically different sponges that had been collected from offshore Ras Mohamed (Egypt) and from Rovinj (Croatia) were investigated by a culture-based approach using different standard media for isolation of actinomycetes and media enriched with aqueous sponge extract to target rare and new actinomycete species. Phylogenetic characterization of 52 representative isolates out of 90 based on almost complete sequences of genes encoding 16S rRNA supported their assignment to 18 different actinomycete genera. Altogether 14 putatively new species were identified based on sequence similarity values below 98.2% to other strains in the NCBI database. The use of M1 agar amended with aqueous sponge extract yielded a putative new genus related to Rubrobacter which highlighting the need for innovative cultivation protocols. Biological activity testing showed that five isolates were active against Gram-positives only, one isolate was active against Candida albicans only and one isolate showed activity against both groups of pathogens. Moreover, the antiparasistic activity was documented for four isolates. These results showed a high diversity of actinomycetes associated with marine sponges as well as highlighted their potential to produce anti-infective agents. The third part of the thesis focused on the isolation and structure elucidation of new bioactive compounds. Streptomyces strain RV15 recovered from sponge Dysidea tupha, was selected for further chemical analysis by virtue of the fact that it exhibited the greatest antimicrobial potential against Staphylococcus aureus as well as Candida albicans among the all tested strains. Moreover, members of the genus Streptomyces are well known as prolific producers of interesting pharmacologically active metabolites. Chemical analysis of the methanolic crude extract using different chromatographic tools yielded four new compounds. The structures of the new compounds were spectroscopically elucidated to be four new cyclic peptides, namely, cyclodysidins A-D. Their bioactivity was tested against different proteases, bacteria and Candida as well as tumor cell lines. The compounds did not show any significant activities at this point.
The one electron oxidation potential of ten TAAs with all permutations of Cl , OMe- and Me-substituents in the three p-positions were determined by CV. The half wave potential of the first oxidation wave correlates linearly with the number of Cl- and OMe-substituents. AM1-CISD derived values of the absorption energies are in good agreement with the experiments but differ strongly for the oscillator strengths as well as for neutral compounds and their corresponding mono radical cations. The small solvent dependence of the experimental UV/Vis spectra in CH2Cl2 and MeCN reflects a minor charge transfer character of the electronic transitions. The UV/Vis/NIR spectra of the series of TAAs and their corresponding radical cations and the AM1 computations reveal that even small substituents may lead to strong symmetry breaking and to a modified electronic structure. The spectroscopic properties of a series of four bis-TAA donor-bridge-donor X-B-X dimers, composed of two asymmetric TAA chromophores (monomers) were investigated. UV/vis-, fluorescence and transient absorption spectra were recorded and compared with those of the corresponding X-B monomers. The excited states of the dimers are described as MV states which show, depending on the chemical nature of the bridge, a varying amount of interactions. It was found that superradiant emission only proceeds in the case of weak and medium coupling. Whether the first excited state potential energy surface of the dimers is a single minimum or a double minimum potential depends on the solvent polarity and the electronic coupling. In the latter case, the dimer relaxes in a symmetry broken CT state. The [2.2]paracyclophane bridged dimer is an example for a weakly coupled system, because the spectroscopic behavior is very similar to the corresponding p xylene monomer. In contrast, anthracene as well as p-xylene bridges mediate a stronger coupling and reveal a significant cooperative influence on the optical properties. A series of [2.2]paracylophane bridged bis-TAA MV radical cations X-B-X+ were analyzed by a GMH three-level model which takes two transitions into account: the IV-CT band and the bridge band. From the GMH analysis, one can conclude that the [2.2]paracyclophane moiety is not the limiting factor which governs the intramolecular charge transfer. The electronic interactions are of course smaller than direct conjugation but from the order of magnitude of the couplings of the [2.2]paracyclophane MV species it can be assumed that this bridge is able to mediate significant through-space and through-bond interactions. From the exponential dependence of the electronic coupling V between the two TAA localized states on the distance r between the two redox centers, it was inferred that the HT proceeds via superexchange mechanism. The analysis reveals that even significantly longer conjugated bridges should still mediate significant electronic interactions, because the decay constant of a series of conjugated MV species is small. The absorption properties of a series of bis-TAA-[2.2]paracyclophane dications X+-B-X+ were presented. The localized and the CT transitions of these dications are explained and analyzed by an exciton coupling model which also considers the photophysical properties of the monomeric TAA radical cations. Together with AM1-CISD calculated transition moments, experimental transition moments and transition energies of the bis-TAA dications were used to calculate electronic couplings by a GMH approach. These couplings are a measure for interactions of the excited MV CT states. The modification of the diabatic states reveals similarities of the GMH three-level model and the exciton coupling model. Comparison of the two models shows that the transition moment between the excited mixed-valence states of the dimer equals the dipole moment difference of the ground and the excited bridge state of the corresponding monomer. Thianthrenophane (1) has a cavity which offers enough room to potentially enable endohedral coordination to small ions or molecules. For the complexation of silver(I) perchlorate, the complex stability constants of thianthrenophane logK1=5.45 and of thianthrene logK2=9.16 were determined by UV/Vis titration. Single competition transport experiments with ten metal salts demonstrate a very high selectivity of thianthrenophane as a carrier for silver(I) and a distinctly higher transport rate compared to carriers such as thianthrene and 14-ane-S4. Although the X-ray crystal structure analysis of the polymeric [Ag(1)]ClO4 shows an exohedral coordination to silver(I), the formation of an endohedral [Ag(1)]+ complex is suggested to be the explanation for the unusual carrier selectivity of silver(I) by 1 in bulk liquid membrane.
Merocyanine Dyes as Organic Semiconductors for Vacuum-processed Solar Cell and Transistor Devices
(2015)
The present thesis comprises the synthesis of new functional merocyanine dyes, the study of their electro-optical properties as well as solid state packing and their application as p-type semiconductor materials in transistor and solar cell devices. The absorption properties of the obtained compounds could be modified by variation of the donor unit, the introduction of electron-withdrawing substituents in the acceptor unit or elongation of the polymethine chain. For a particular dye, the absorption band could be shifted by more than 160 nm by increasing the solvent polarity due to a conformational switch between a merocyanine-like and a cyanine-like structure. Single crystal analyses revealed that the studied dyes tend to pack either in an antiparallel fashion forming dimers with no overall dipole moment or in a staircase-like pattern where the dipole moments point to the same direction and are only balanced by another staircase oriented in the opposite direction (stair dimer). With respect to application as semiconductor materials, the latter packing arrangement resulted most favorable for charge carrier mobility. We concluded that this packing motif is preserved in the solar cell devices, where the selenium-containing dye afforded the highest performance of this series for an optimized planar-mixed heterojunction solar cell (6.2 %).
Oxygen-centered radicals are important intermediates in photobiological, mechanistic and synthetic studies. The majority of precursors of reactive oxyl radicals are labile and thus delicate to handle. Therefore N-(alkoxy)-pyridinethiones and N-(Alkoxy)-thiazolethiones have attracted attention as "mild'' photochemical source of alkoxyl radicals, in the last few years. A disadvantage of the pyridine compounds, is their sensibility to daylight. Despite of their similarities, both molecules behave surprisingly different, if photolyzed in the absence of trapping reagents. The pyridinethione compounds undergo highly efficient radical chain reactions under such conditions while the corresponding thiazolethiones react surprisingly sluggish and give rise to several unwanted side products. The properties of both compounds should be understood and optimized in the frame of this work. Additionally new compounds should be suggested that can also be applied in the photochemical alkoxyl radical generation. Some background information about the generation and application of alkoxyl radicals is provided in chapter 2. Electronic excitations and UV/vis spectroscopy together with a description of quantum chemical approaches that are able to calculate such phenomena are outlined in chapter 3. Chapter 4 deals with the description of the vertical excitation spectra. During the validation CASSCF, CASPT2, TD-DFT and RI-CC2 were tested with respect to their ability to describe the vertical excitations in both compounds. The CASPT2 approach gives accurate descriptions of the electronic excitation spectra of all compounds. The time-dependent DFT results are very sensitive on the choice of the functional and a validation of the results should be always done. On the basis of these computations the spectroscopic visible absorption bands of both compounds were assigned to a pi-->pi* transition in the thiohydroxamic acid functionality. In chapter 5 the mechanism of the thermally and the photochemically induced N,O homolysis in both compounds is unveiled. The near UV-induced N,O homolysis will start from the S2 state. The expected relaxation from the S2- to the S1-state and the dissociation process is expected to be very fast in the case of the thiazolethione compound. The potential surfaces of the pyridine compound in contrast point to a slower N,O bond dissociation. Due to the resulting faster dissociation process the excess energy which results from the photochemical activation is quenched only to small amounts. The maximal possible excess energy of the fragments is lower and a quenching is much more likely in the case of the pyridinethione compounds. This explaines the different reactivities of both compounds. For the also already successfully applied precursor system N-(alkoxy)-pyridineones the computed dissociation paths show courses that clearly predict a slow bond dissociation process. Chapter 6 deals with the tuning of the initial excitation wave length of the known pyridinethiones und thiazolethiones. In the first part the effects of substituents on the thiazolethione heterocycle was examined. The UV/vis spectra of 4 and 5 substituted thiazolethiones can be interpreted like the spectrum of the parent compound. The second part of chapter 6 deals with the identification of a substitution pattern on the pyridine heterocycle which induces a blue shift of the photo active band. The computations showed that electron rich and electron poor substituents result the same effects on the electronic excitation spectra. These substituent effects are additive, but the steric orientation of the substituents has to be taken into account. Chapter 7 describes a computer aided design of new alkoxyl radical precursors. Combining the advantages of both compounds the radical formation should be initiated by an irradiation with light at about 350 nm, and the amount of side products during the radical formation process should be small. To achieve this 18 test candidates were obtained by a systematic variation of the parent compound of the thiazolethione precursor. To identify the promising new precursor systems a screening of the lower electronic excitations of all resulting 18 systems was performed with TD-DFT. For promising systems the N,O or P,O dissociation paths, respectively, were analyzed according to the developed model. N-(methoxy)-azaphospholethione and N-(methoxy)-pyrrolethione seem to be the most promising candidates. The computations predict a strong absorption at about 350 nm respectively 320 nm. Due to the amounts of maximal excess energy and the shapes of the potential surfaces of the N,O bond dissociation paths their reactivity should resemble more the behavior of the pyridinethiones.
In this work the energy transfer and excitonic coupling in different chromophore arrangements were investigated. A difference in the coupling strength was introduced by varring the connecting unit and the spacial orientation relative to each other.
The synthesis of the 2,7-substituted pyrene compounds could be optimised and good yields of HAB 1 and HAB 2 and small amounts of HAB 2 could be achieved by cobalt-catalysed trimerisation or Diels Alder reaction in the end. Absorption and fluorescence spectra reveal strong intramolecular interactions between the pyrene molecules in the HAB 1. Excitation spectra recorded at the high and low energy fluorescence suggest the contribution of two components to the spectra. One being similar to the ground state aggregate and a second species similar to undisturbed pyrene. All these feature can be accounted to two different fluorescent states which are due to electronical decoupling in the excited state. Due to the strong intramolecular coupling already in the ground state of the molecule, no energy transfer could be studied, as the six pyrene units cannot be seen as separate spectroscopic entities between which energy could be transferred.
In the second part of this thesis dye conjugates of different size and alignment were synthesised to study the interaction of the transition-dipole moments. Therefore a systematic investigation of Sonogashira conditions was performed in order to obtain good yields of the desired compounds and keep dehalogenation at a minimum level. Nevertheless only the symmetrical triads could be purified as the asymmeric triads and pentades proved to decompose during purification.
The pyrene containing triads Py2B and Py2SQB show small interactions already in the ground state represented by red shifts of the spectra and a broadening of the bands. Nevertheless, these interactions are in the weak coupling regime and energy transfer between the constituents is possible. On the contrary in the TA spectra it is obvious that always the whole triad, at least to some extend is excited. To question if the excitation of the high energy state is deactivated by energy transfer or rather IC in a superchromophore could not be distinguished in the course of this work. At present additional time-dependent calculations of the dynamics are in progress to get a deeper understanding of the photophysical processes taking place in the triads.
The dye conjugates B2SQB-3 and (SQB)2B-4 can be assigned to the strong interaction range and hence are describable by exciton theory. The transition-dipole moments proved to be more than additive and increase for both compounds from absorption to fluorescence. This can be explained by an enhancement of the coupling in the relaxed excited state compared to the absorption into the Franck-Condon state due to a more steep potential energy surface in the excited state and hence smaller fluctuations.
In the last part of this thesis the influence of disrupting electronical communication by implementing a rigid non-conjugated bridge in a bichromophoric trans-squaraine system was tested. While the flexible linked squaraines show complex spectra due to different conformers the SQA2Anth compound is rigified and no rotation is possible. This change in flexibility is represented in the steady-state spectra where just one main absorption and fluorescence band is present due to a single allowed excitonic state. The system proves to own an excited state that is completely delocalised over the whole molecule.
In this thesis, the usage of onion-like carbon (OLC) for energy storage applications was researched regarding sustainability, performance and processability. This work targets to increase the scientific understanding regarding the role of OLC in electrodes and to facilitate a large-scale production, which is the foundation for commercial application. Research was devoted to increase the knowledge in the particular field, to yield synergistic approaches and a shared value regarding sustainability and performance.
This thesis concerned the quantification of cell adhesion molecules (CAM) in and on thin hydrogel films as surface modification of biomaterials. The established and well characterized, per se inert NCO-sP(EO-stat-PO) hydrogel system which allows the easy and reproducible bioactivation with peptides was used as basis for this thesis. Two methods can be used to functionalize the coatings. Ligands can either be mixed into the prepolymer solution in prior to layer formation (mix-in method), or freshly prepared coatings can be incubated with ligand solution (incubation method). Divided into three major parts, the first part of the thesis dealt with the concentration of ligands in the bulk hydrogel, whereas the second part of the thesis focused on the surface sensitive quantification of CAMs at the biointerface. The results were correlated with cell adhesion kinetics. The third part of this thesis investigated the biochemical and the structural mimicry of the extracellular matrix (ECM). ECM proteins were presented via sugar-lectin mediated binding and cell behavior on these surfaces was analyzed. Cell behavior on three-dimensional fibers with identical surface chemistry as the coatings in the previous sections of the thesis was analyzed and correlated with the amount of peptide used for bioactivation. Overall, the main question of this work was ‘How much?’ regarding maximal as well as optimal ligand concentrations for controlled cell-hydrogel interactions. The focus in the first practical part of this thesis was to analyze the amount of ligands in NCO-sP(EO-stat-PO) hydrogels using classical quantification methods. Coatings in 96-well plates as well as on glass were functionalized with GRGDS and 125I-YRGDS for radioisotopic detection (Chapter 3). Using the incubation method for functionalization, a maximal ligand binding using peptide concentrations of 600 µg/mL could be determined. When functionalization was introduced via the mix-in method, a clear tendency for higher ligand concentrations with increasing ligand to prepolymer ratio was observed, but no maximal ligand binding could be detected with a ligand to prepolymer ratio of 2/1 being the highest ratio investigated. This ratio of 2/1 was not exceeded to ensure that complete crosslinking of the hydrogel was not affected. In Chapter 4, a fluorinated amino acid and an iodinated peptide were immobilized to the hydrogels using the mix-in method and were detected by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). In these measurements, maximal ligand binding was detected for a ligand to prepolymer ratio of 1/1. Higher ligand to prepolymer ratios did not result in any significant increase in ligand concentrations in the surface near regions of the crosslinked hydrogels. To address the question of how many ligands were actually accessible for cell interaction at the interface, surface sensitive quantification methods were applied in the second part of this thesis. For the quantification with surface plasmon resonance (SPR) and surface acoustic wave technology (SAW) (Chapter 5), the hydrogel coating procedure needed to be transferred onto cystamine functionalized gold surfaces. Characterization with ellipsometry and atomic force microscopy (AFM) revealed inhomogeneous cystamine binding to the activated surfaces, which resulted in inhomogeneous coatings. Nevertheless, it could be shown that SPR as well as SAW were suitable methods for the surface sensitive quantification of the ligand concentration on NCO-sP(EO-stat-PO) hydrogels. Non-functionalized coatings resisted non-specific serum as well as streptavidin (SA) adsorption. Coatings functionalized with biocytin and GRGDSK-biotin introduced specific SA binding that was dependent on the biotin concentration at the surface. Additionally, enzyme linked immunosorbent assay (ELISA) and enzyme linked lectin assay (ELLA) (Chapter 6) were applied to coatings in 96-well plates and on glass. Coatings were functionalized with the model molecule biocytin, the biotinylated peptide GRGDSK-biotin, the ECM protein fibronectin (FN), as well as the carbohydrates N-acetylglucosamine (GlcNAc) and N-acetyllactosamine (LacNAc). All ligands could be successfully detected with antibodies or SA via ELISA or ELLA. Maximal GRGDSK-biotin binding to the hydrogel coatings on glass was achieved at a peptide to prepolymer ratio of 1/5, which was used as reference value in Chapter 8. Last but not least, cell adhesion (Chapter 7) was quantified depending on the GRGDS concentration on hydrogel coatings on glass. Maximal adhesion of primary human dermal fibroblast (HDF) was observed at GRGDS to prepolymer ratios of 1/5, when adherent cells were counted on life cell images. Quantification of adherent cells using the CASY® cell counter revealed maximal HDF adhesion at molar ligand to prepolymer ratios of 1/2. However, cell vitality detected by intracellular enzyme activities was not dependent on the GRGDS concentration. Cells which managed to adhere were vital regardless of the amount of ligands present. Additionally, adhesion of fibroblasts from the murine cell line NIH L929 was analyzed by counting on life cell images. These cells, being much smaller than the HDF cells, needed higher GRGDS to prepolymer ratios (2/1) for proper cell adhesion. All quantification methods applied to analyze hydrogels which were functionalized by the mix-in method in Chapter 3, 4, 6 and 7, were compared in Chapter 8. Radiodetection gave information about the ligand concentrations throughout the whole hydrogel and no maximal amount of ligands could be detected when increasing the peptide to prepolymer ratio. In contrast, XPS and TOF-SIMS which only penetrated the surface near regions of the coating, a maximal ligand binding to the hydrogel was detected for 1/1 ratios. SPR and SAW were not included in this comparison, as the coatings on gold need to be optimized first. The two surface sensitive quantification methods (ELISA and HDF adhesion) could give information about the quantity of peptide which was sterically available for SA or cell binding. With these methods, maximal SA and cell binding was detected at ratios of 1/5. These results underline the importance of carefully compare the different methods. Beside ligand quantification on hydrogels, the third part of this thesis was concerned with the biochemical and structural mimicry of the ECM by advanced ECM engineering to design biomimetic biomaterials that are better accepted by cells and tissue. The subject of Chapter 9 was the biomimetic and flexible presentation of the ECM protein FN. FN was attached via sugar-lectin mediated binding to NCO-sP(EO-stat-PO) hydrogels. The build-up of the covalently immobilized sugar poly-N-acetyllactosamine (polyLacNAc), the subsequent non-covalent binding of the fungal galectin His6CGL2, and FN could be elegantly proven by fluorescent staining on coatings which were functionalized with the sugar by micro contact printing (MCP). Further experiments were carried out on build-ups, where polyLacNAc was immobilized on the hydrogel by incubation. Optimal parameters for the layer build-up were determined by ELLA/ELISA. Only the complete build-up induced proper adhesion of HDFs. Compared to tissue culture polystyrene (TCPS), cells adhered and spread faster on the biomimetic surfaces. The flexible presentation of FN allowed HDFs to rearrange homogenously immobilized FN into fibrillar structures, which seemed not to be possible when FN was adsorbed on glass or covalently bound directly to the hydrogel coatings. This new approach of a flexible and biomimetic presentation of an ECM protein allows new ways to design biomaterials with best possible cell-material interactions. The work described in Chapter 10 focused on the structural mimicry of the fibrous ECM structures by electrospinning of synthetic, bioactive, and degradable fibers. Poly(D,L-lactide-co-glycolide) (PLGA) and NCO-sP(EO-stat-PO) were electrospun out of one solution in an easy one-step preparation resulting in fibers with an ultrathin inert hydrogel layer at the surface. By adding GRGDS to the solution prior to electrospinning, specifically interacting fibers could be obtained. In comparison to PLGA, the adsorption of bovine serum albumin (BSA) could be reduced by 99.2%. As a control, the non-active peptide GRGES was immobilized to the fiber. These fibers did not allow cell adhesion, showing that the integrity of the hydrogel coated fibers was not affected by the immobilization of peptides. HDF adhesion was obtained by functionalization with GRGDS, leading to the adhesion, spreading, and proliferation of HDFs. Also mesenchymal stem cells (MSC) could adhere to GRGDS functionalized fibers. Additionally, for ligand quantification, the ELISA technique was successfully transferred to fiber substrates. To highlight the potential of the approaches for the biochemical and structural mimicry of the ECM, the sugar polyLacNAc was immobilized on the PLGA/sP(EO-stat-PO) fibers followed by the subsequent layer build-up with His6CGL2 and FN. These fibers triggered HDF adhesion.
The thesis enhances the strategy of non-destructive fluorescence read-out in rylene bisimide-diarylethene containing photochromic systems. The fluorescence of the emitter unit is quenched by a photoinduced electron transfer only to one of the isomeric forms of the photochrome. The driving force of the fuorescence-quenching electron transfer was calculated by the help of the Rehm-Weller equation. The novel photochromic systems satisfy the necessary requirements for non-destructive read-out in write/read/erase fluorescent memory devices.
Galectin-1 (hGal-1) is overexpressed by numerous cancer types and previously conducted studies confirmed that the β-galactoside-binding protein mediates various molecular interactions associated with tumor growth, spread and survival. Upon interaction with carbohydrate-based binding epitopes of glycan structures on human cell surfaces galectin-1 induces proliferative, angiogenetic and migratory signals and modulates negative T cell regulation which essentially helps the tumor to evade the immune response. These findings attributed galectin-1 a pivotal role in tumor physiology and strongly suggest the protein as target for diagnostic and therapeutic applications.
Within the scope of this work a strategy was elaborated for designing tailor-made galectin-1 ligands by functionalizing selected hydroxyl groups of the natural binding partner N-acetyllactosamine (LacNAc) that are not involved in the sophisticated interplay between the disaccharide and the protein. Synthetic modifications intended to introduce chemical groups i) to address a potential binding site adjacent to the carbohydrate recognition domain (CRD) with extended hGal-1-ligand interactions, ii) to implement a tracer isotope for diagnostic detection and iii) to install a linker unit for immobilization on microarrays.
Resulting structures were investigated regarding their targeting ability towards galectin-1 by cocrystallization experiments, SPR and ITC studies. Potent binders were further probed for their diagnostic potential to trace elevated galectin-1 levels in microarray experiments and for an application in positron emission tomography (PET).
A series of donor-acceptor macrocyclic architectures comprising oligothiophene strands that connect the imide positions of a perylene bisimide have been synthesized via a platinum-mediated cross-coupling strategy. The target structures were characterized by steady-state UV/Vis absorption, fluorescence and transient absorption spectroscopy, as well as cyclic and differential pulse voltammetry. Crystal structure analysis of the macrocycles revealed insights into the bridge arrangements. The properties of the macrocyclic bridges were compared to linear oligothiophene reference compounds which itself exhibited an unusual electrochemical effect.
The aim of this work was the selective functionalisation of tribenzotriquinacene (TBTQ) in order to extend the aromatic system and tune the electronic properties. The synthesised molecules could be starting materials for a model system of a defective graphene fragment. The “triple cyclisation pathway” by Hopf et al. was adapted and fluorinated tribenzotriquinacenes were synthesised for the first time.
Phenanthrene groups were also introduced in other model systems and the crystal structures of phenanthrene functionalised TBTQs were compared with the parent molecules.
In addition, the arrangement of TBTQ and centro methyl functionalised TBTQ was investigated on a Ag(111) surface for the first time using scanning transmission microscopy (STM). Different arrangements were observed, depending on the coverage of the surface.
The insights gained about the interaction between TBTQs as well as their synthesis provide a foundation for further work and potential applications as components in organic electronic devices.
The technology of organic photovoltaics offers the possibility of low-cost devices due to easy fabrication procedures and low material consumption and at the same time high flexibility concerning the applied substrates or design features such as the color palette. Owing to these benefits, this research field is highly active, being reflected by the continuously rising number of publications. Chapter 1 gives an extensive overview of a part of these reports, namely the field of solution-processed BHJ organic solar cells using small molecules as electron-donating materials. In the early years of this research area (2006-2008), well known hole transporting materials such as triphenylamine based chromophores, oligothiophenes and polyaromatic hydrocarbons were applied. However, many of these dyes lacked absorption at longer wavelengths and were therefore limited in their light harvesting qualities. Later, chromophores based on low band gap systems consisting of electron-donating and electron-accepting units showing internal charge transfer overcame this handicap. Today, donor-substituted diketopyrrolopyrroles (D-A-D chromophores), squaraines (D-A-D chromophores) and acceptor substituted oligothiophenes (A-D-A chromophores) are among the most promising dyes for small molecule based organic solar cells with PCEs of 4-5%. This work is based on the findings of the groups of Würthner and Meerholz, which tested merocyanine dyes for the first time in organic BHJ solar cells.4 According to the Bässler theory85, the high dipolarity of these dyes should hamper the charge transport, but the obtained first results with PCE of 1.7% proved the potenital of this class of dyes for this application. Merocyanine dyes offer the advantages of facile synthesis and purification, high tinctorial strength and monodispersity. Additionally, the electronic structure of the dyes, namely the absorption as well as the electrochemical properties, can be adjusted by using the right combination of donor and acceptor units. For these reasons, this class of dye is highly interesting for the application in organic solar cells. It was the aim of the thesis to build more knowledge about the potential and limitations of merocyanines in BHJ photovoltaic devices. By screening a variety of donor and acceptor groups a comprehensive data set both for the molecular materials as well as for the respective solar devices was generated and analyzed. As one focus, the arrangement of the chromophores in the solid state was investigated to gain insight about the packing in the solar cells and its relevance for the performance of the latter. To do so, X-ray single crystal analyses were performed for selected molecules. By means of correlations between molecular properties and the characteristics of the corresponding solar cells, several design rules to generate efficient chromophores for organic photovoltaics were developed. The different donor and acceptor moieties applied in this work are depicted in the following ...
In this work the successful synthesis, the linear and nonlinear spectroscopic properties as well as the electrochemical behaviour of some linear and star-shaped squaraine superchromophores that are based on indolenine derivatives were presented. The attempt to synthesise similar chromophores which contained only benzothiazole squaraines failed unfortunately. However, one trimer that contained mixed benzothiazole indolenine squaraines could be synthesised and investigated as well.
The linear spectroscopic properties, like red-shift and broadening of the absorption, of all superchromophores could be explained by exciton coupling theory. The heterochromophores (SQA)2(SQB)-N, (SQA)(SQB)2-N and (SQA)(SQB)-NH displayed additional to the typical squaraine fluorescence from the lowest excited state some properties that could be assigned to localised states. While the chromophores with N-core showed very small emission quantum yields, the chromophores with the other cores and the linear oligomers display an enhancement compared to the monomers.
Transient absorption spectroscopy experiments of the star-shaped superchromophores showed, that their formally degenerated S1 states are split due to a deviation of the ideal C3 symmetry. This is also the reason for the observation of an absorption band for the highest exciton state, which is derived from the S1-state of the monomers, as its transition-dipole moment would be zero in the symmetrical case.
The linear oligomers and the star-shaped superchromophores with a benzene or triarylamine core showed at least additive, sometimes even weak cooperative, behaviour in the two-photon absorption experiments. Additional to higher two-photon absorption cross sections the chromophores showed a pronounced broadening of the nonlinear absorption, due to symmetry breaking and a higher density of states.
Unfortunately it was not possible to solve the problem of the equilibrium of the cisoid and the transoid structure of donor substituted azulene squaraines, due to either instability of the squaraines or steric hindrance.
As a traditional industrial pigment, perylene bisimide (PBI) dyes have found wide-spread applications. In addition, PBI dyes have been considered as versatile and promising functional materials for organic-based electronic and optic devices, such as transistors and solar cells. For these novel demands, the control of self-organization of this type of dye and the investigation of the relationship between the supramolecular structure and the relevant optical and electronic properties is of great importance. The objective of this thesis focuses on gaining a better understanding of structural and functional properties of pi-stacks based on self-assembling PBIs. Studies include the synthesis and characterization of new functional PBI dyes, their aggregation in solution, in liquid crystalline state and on surfaces, and their fluorescence and charge transport properties. An overview of the formation, thermodynamics and structures of pi-stacks of functional pi- conjugated molecules in solution and in liquid crystalline phases is given in Chapter 2. Chapters 3 and 4 deal with the pi-pi aggregates of new, highly fluorescent PBIs without core-substituents. In Chapter 3, the self-assembly of a PBI with tridodecylphenyl substituents at imide N atoms both in solution and condensed phase has been studied in great detail. In condensed state, the dye exhibits a hexagonal columnar liquid crystalline (LC) phase as confirmed by DSC, OPM and X-ray diffraction analysis. The columnar stacking of this dye has been further confirmed by atomic force microscopy (AFM) where single columns could be well resolved The charge transport properties this dye have been investigated by pulse radiolysis-time resolved microwave conductivity (PR-TRMC) measurements. To shed more light on the nature of the pi-pi interaction of the unsubstituted PBIs, solvent depend aggregation properties have been investigated in Chapter 4. The studies are further extended from core-unsubstituted PBIs to core-substituted ones (Chapter 5 and 6). In Chapter 5, a series of highly soluble and fluorescent core-twisted PBIs that bear the same trialkylphenyl groups at the imide positions but different bay-substituents and were synthesized. These compounds are characterized by distortions of the perylene planes with dihedral angles in the range of 15-37° according to crystallographic data and molecular modeling studies. In contrast to the extended oligomeric aggregates formed for planar unsubstituted PBIs, this family of dyes formed discrete pi-pi-stacked dimers in apolar methylcyclohexane as concentration-dependent UV/Vis measurements and VPO analysis revealed. The Gibbs free energy of dimerization can be correlated with the twist angles of the dyes linearly. In condensed state, several of these PBIs form luminescent rectangular or hexagonal columnar liquid crystalline phases with low isotropization temperatures. The core-twisting effect on semiconducting properties has been examined in Chapter 6. In this chapter, a comparative study of the electrochemical and the charge transport properties of a series of non-substituted and chlorine-functionalized PBIs was performed. While Chapters 3-6 focus on one-component dye systems, Chapter 7 explored the possibility of a supramolecular engineering of co-aggregates formed by hydrogen-bonded 2:1 and 1:1 complex of oligo(p-phenylene vinylene)s (OPVs) and PBIs. Covalently linked donor-acceptor dye arrays have been prepared for comparison. Concentration and temperature-dependent UV/Vis spectroscopy revealed all hydrogen-bonded and covalent systems form well-ordered J-type aggregates in methylcyclohexane. With these hydrogen-bonded OPV-PBI complexes, fibers containing p-type and n-type molecules can be prepared on the nano-scale (1-20 nm). For the 2:1 OPV-PBI hydrogenbonded arrays hierarchically assembled chiral superstructures consisting of left-handed helical pi-pi co-aggregates (CD spectroscopy) of the two dyes that further assemble into right-handed nanometer-scale supercoils in the solid state (AFM study) have been observed. All of these well-defined OPV-PBI assemblies presented here exhibit photoinduced electron transfer on sub-ps timescale, while the electron recombination differs for different systems.Thus, it was suggested that such assemblies of p- and n-type semiconductors might serve as valuable nanoscopic functional units for organic electronics.
Synthesis and Characterization of an Oligo(Phenylene Ethynylene)-Based Perylene Bisimide Foldamer
(2010)
The present work is part of the currently only rudimentary understanding of the structure-property relationships in the self-assembly of pi-conjugated organic molecules. Such structures may reveal favorable photophysical and semiconducting properties due to the weak non-covalent pi-pi interactions between the monomer units. The specific mutual orientation of the dyes is known to evoke individual functional properties for the condensed matter, however, the related electronic processes are still not well-understood and further enhancements of functional properties are seldom triggered by rational design. The pi-pi self-assembly structures of perylene bisimide (PBI) dyes are promising, versatile materials for organic electronic devices and have been elected for this thesis as an archetype aggregate system to investigate the dye-dye interactions in more detail. In cooperation with experts in the field of spectroscopy and theory the development of reliable routines towards a better understanding of the origins of the functional properties may be feasible, and, on a longer time-line, such knowledge may enable optimization of functional organic materials. Having designed such structures entailed the challenge of developing feasible synthesis strategies, and to actually generate the targeted molecules by synthesis. Several synthesis approaches were conducted until finally a perylene bisimide foldamer was obtained based on a Sonogashira co-polymerization reaction. After purification and enrichment of the larger-sized species by means of semi-preparative gel permeation chromatography (GPC) the average size of an octamer (8500 Da) species was determined by analytical GPC. The low polydispersity index (PD) of 1.1 is indicative of a sharp size distribution of the oligomers. This average size was confirmed by performing diffusion ordered NMR spectroscopy (DOSY). Furthermore, MALDI-TOF mass analysis substantiated the structural integrity of the co-polymerization product. Solvent-dependent UV/vis spectroscopic investigations demonstrated that intramolecular PBI aggregates are reversibly formed, indicating that this oligomer is able to fold and unfold in the intended manner upon changing external conditions. In the unfolded states, the PBI moieties are closely arranged due to the short OPE bridges (< 2.4 nm), which is expressed by an exciton coupling interaction of the dyes and therefore the characteristic monomer absorption pattern of the PBI chromophore cannot be obtained in the unfolded states. More interestingly, the folded state revealed a pronounced aggregate spectrum of the PBIs, however, striking differences in the shape of the absorption spectrum compared to our previously investigated PBI self-assembly were obtained.
Within this thesis, synthetic strategies for self-assembled organic cage compounds have been developed that allow for both stimuli-responsive control over assembly/disassembly processes and spatial control over functionalization. To purposefully operate the reversible assembly of organic cages, boron-nitrogen dative bonds have been exploited for the formation of a well-defined, discrete bipyramidal organic assembly in solution. Thermodynamic association equilibria for cage formation have been investigated by Isothermal Titration Calorimetry (ITC). Temperature-dependent NMR studies revealed a reversible cage opening upon heating and quantitative reassembly upon cooling. For the spatial functionalization of organic cages, two divergent molecular building units have been designed and synthesized, namely tribenzotriquinacene derivatives possessing a terminal alkyne moiety at the apical position and a meta-diboronic acid having a pyridyl group at the 2-position. Facile access to a variety of apically functionalized tribenzotriquinacenes has been illustrated by post-synthetic modifications at the terminal alkyne group by Sonogashira cross-coupling and azide-alkyne click reactions. Finally, these apically functionalized tribenzotriquinacene building blocks have been implemented into boronate ester-based organic cage compounds showing modular exohedral functionalities.
Nucleic acids are not only one of the most important classes of macromolecules in biochemistry but also a promising platform for the defined arrangement of chromophores. Thanks to their precise organization by directional polar and hydrophobic interactions, oligonucleotides can be exploited as suitable templates for multichromophore assemblies with predictable properties. To expand the toolbox of emissive, base pairing nucleobase analogs several barbituric acid merocyanine (BAM) chromophores with tunable spectroscopic properties were synthesized and incorporated into RNA, DNA and glycol nucleic acid (GNA) oligonucleotides. A multitude of duplexes containing up to ten BAM chromophores was obtained and analysis by spectroscopic methods revealed the presence of dipolarly coupled merocyanine aggregates with properties
strongly dependent on the chromophore orientation toward each other and the backbone conformation. These characteristics were exploited for various applications such as FRET pair formation and polymerase chain reaction (PCR) experiments. The observed formation of higher-order aggregates implies future applications of these new oligonucleotide-chromophore systems as light-harvesting DNA nanomaterials. Besides oligonucleotide templated covalent assembly of chromophores also non-covalent nucleic acid-chromophore complexes are a broad field of research. Among these, fluorogenic RNA aptamers are of special interest with the most versatile ones based on derivatives of the GFP chromophore hydroxybenzylidene imidazolone (HBI). Therefore, new HBI-derived chromophores with an expanded conjugated system and an additional exocyclic amino group for an enhanced binding affinity were synthesized and analyzed in complex with the Chili aptamer. Among these, structurally new fluorogenes with strong fluorescence activation upon binding to Chili were identified which are promising for further derivatization and application as color-switching sensor devices for example.
Complexation properties of 2,2':6',2''-terpyridine (tpy) have been studied with a series of first row transition metal ions by UV-vis, 1H NMR and isothermal titration calorimetry and ƒ´H values for the tpy complexation processes have been determined. These studies reveal that Zn2+ is the best suited metal ion for the reversible coordination of the terpyridine ligand. Thus, supramolecular coordination polymerization of perylene bisimide fluorophores containing terpyridine functionalities have been investigated by using Zn2+ as metal ion. The formation of the dimeric complexes in the case of monotopic model comounds and coordination polymerization of ditopic functional building blocks have been confirmed by 1H NMR studies. The optical properties of dimeric and polymeric complexes have been investigated by UV-vis and fluorescence spectroscopy. The Zn2+ coordination to the terpyridine unit does not effect the advantageous fluorescence properties of perylene bisimide moieties. The reversibility of the formation of coordination polymers has been established by 1H NMR and additionally by DOSY NMR and fluorescence anisotropy measurements. Coordination polymer strands can be visualized by atomic force microscopy (AFM), which also reveals the formation of an ordered monolayer film at higher concentration. The average polymer length has been determined by AFM to 15 repeat units, which correlates well with the value estimated by 1H NMR to >10 repeat units.
In this work, a series of redox cascades was synthesised and investigated in view of their photophysical and electrochemical properties. The cascades are based on a perchlorinated triphenylmethyl radical acceptor and two triarylamine donors. Absorption spectra showed the presence of charge-transfer bands in the NIR range of the spectra, which pointed to the population of a charge-transfer state between a triarylamine donor and the radical acceptor. A weak to moderate emission in the NIR range of the spectra was observed for all compounds in cyclohexane. Spectroelectrochemical measurements were used to investigate the characteristic spectral features of the oxidised and reduced species of all compounds. Transient absorption spectra in the ns- and fs-time regime revealed an additional hole transfer in the cascades between the triarylamine donors, resulting in a charge-separated state. Charge-separation and -recombination processes were found to be located in the ps-time regime.
This thesis deals with the isolation and structural elucidation of bioactive naphthylisoquinoline alkaloids and related analogs. The mode of action of the antiplasmodial activity exhibited by the naphthylisoquinoline alkaloids was explored and compared to that of the antimalarial drug chloroquine. Furthermore, the phase 1 and 2 metabolism of dioncophyllines A and C and dioncopeltine A were investigated. In detail the following results have been obtained: • From the leaves of the recently discovered East African liana A. tanzaniensis six naphthylisoquinoline alkaloids were isolated. • The leaves of a botanical yet undescribed Ancistrocladus species, collected by Prof. Dr. V. Mudogo in the Democratic Republic of Congo in the habitat Yeteto near the town Ikela, were analyzed for naphthylisoquinoline alkaloids for the first time. The isolation work led to the first identification of an N,C-coupled naphthyldihydroisoquinoline alkaloid; ancistrocladinium B. Phytochemical investigation of the roots of the Congolese Ancistrocladus species (habitat Yeteto), , afforded five new derivatives of known naphthylisoquinoline alkaloids, namely 5'-O-demethylhamatine, 5'-O-demethylhamatinine, 6-O-demethylancistroealaine A, 6,5'-O,O-didemethylancistroealaine A, and 5-epi-6-O-methylancistrobertsonine A, along with six known naphthylisoquinoline alkaloids. • The antiplasmodial activity guided purification of 60Co irradiated samples containing commercially available naphthylisoquinoline related substances, afforded the isolation of the irradiation products 3,4-dihydro-1-isoquinolinone, 3,4-dihydro-1-isoquinolineamine, and 1,2,3,4-tetrahydro-1,2-diazirino-isoquinoline. The compounds were found to be more active than the starting material, although only exhibiting weak antiplasmodial activity against P. falciparum. • The effect on the absorption spectrum of FPIX due to complex formation with the naphthylisoquinoline alkaloids dioncophyllines A and C, dioncopeltine A korupensamine A, and ancistrocladine was examined by a titration study. Job's plot analyses by UV-spectroscopy determined the stoichiometry for the complex formation of FPIX and naphthylisoquinoline alkaloids to be 2:1. Furthermore, the dissociation constants for the complexation with FPIX were determined for each of the naphthylisoquinoline alkaloids investigated. Dioncophylline C and dioncopeltine A were found to possess dissociation constants, which are comparable to the one reported for the antimalarial drug chloroquine. The ability of ESI to transfer noncovalent solution-phase assemblies intact into the gas phase, was conducted on solution mixtures of naphthylisoquinoline alkaloid and FPIX, as well as on mixtures of chloroquine and FPIX. The mass spectrometry analyses revealed several peaks, which corresponded to the complex formation of FPIX to the respective ligands investigated. The most interesting results obtained were the detection of peaks corresponding to the complex formation between a chelated dimer of FPIX and dioncophylline Cand of peaks corresponding to a double protonated tetramer of FPIX – consisting of two chelated -oxo dimers of FPIX – in complex formation with two molecules of chloroquine. • Two phase 1 metabolism products of dioncophylline A were identified. Coelution in combination with HPLC-MS/MS, NMR, and CD investigations assigned the major metabolic product as 5'-O-demethyldioncophylline A. The minor metabolic product was only present in small amounts, which disabled an unambiguous structural characterization of the compound. However, as deduced from the mass spectrometry analyses and exclusion of a possible metabolic oxidation product by coelution with authentic reference material, the metabolite should possess a 4-hydroxylated isoquinoline portion and is assumed to be represented by structure. Dioncophylline C and dioncopeltine A were found to be stable to phase 1 metabolism reactions caused by rat liver microsomes.
In this thesis the syntheses and detailed investigations on two foldable PBI systems were presented. The reversible, solvent-dependet folding/unfolding-behavior was used to study the ground and excited states properties of folda-dimer and folda-trimer by means of different spectroscopic methods as well as theoretical studies. The switching between charge transfer or excimer formation pathways of photoexcited molecules influenced by the spatial arrangement of chromophores within defined dye systems illustrates the impact of conformational preferences on functional properties.
The present thesis encompasses two parts. The first supramolecular part focuses on the development of new flexible self-assembling zwitterions as building blocks for supramolecular polymers. In the second part, the aim was to develop bioorganic receptors for amino acids and dipeptides in aqueous media. Both research projects are based on the guanidiniocarbonyl pyrrole 1 as a new efficient binding motif for the complexation of carboxylates in polar solution.A necessary requirement for the realization of these research projects was to develop an efficient and mild synthetic approach for the cationic guanidiniocarbonyl pyrroles in general. The harsh reaction conditions of the previously used method and the problematic purification of the cationic guanidinocarbonyl pyrroles so far prevented a more extensive exploration in bioorganic and supramolecular research. In the course of this work I successfully developed a new synthesis starting with mono tBoc-protected guanidine that was coupled with a benzyl protected pyrrole carboxylic acid. After deprotection of the benzyl group, a key intermediate in the newly developed synthesis, the tBoc-protected guanidinocarbonyl pyrrole acid, was obtained. This new, mild and extremely efficient synthetic approach for the introduction of acyl guanidines is now the standard procedure in our group for the preparation of both solution and solid-phase guanidiniocarbonyl pyrroles. With this facile method at hand, a new class of flexible zwitterions, in which a carboxylate is linked via an alkyl chain to a guanidiniocarbonyl pyrrole cation was synthesized. The self-aggregation and the influence of the length and therefore flexibility of the alkyl spacer on the structure and stability of the formed aggregates were studied in solution and gas phase. In solution the aggregation was studied by NMR-dilution experiments in DMSO which suggest that flexible zwitterions with n = 1, 3 and 5 form oligomers. For n = 1, highly stable helical aggregates with nanometer size are formed. In the gas phase studies the stability and the fragmentation kinetics of a series of sodiated dimeric zwitterions with n = 2, 3 and 5 were investigated. This was done by infrared multiphoton dissociation Fourier transform ion cyclotron resonance mass spectrometry (IRMPD-FT-ICR-MS). These kinds of studies can be used in the future for a more directed design of supramolecular building blocks The bioorganic research part comprises three different projects. In a first project I synthesized four new arginine analogues which can be implemented in peptides as a substitute for arginine. Therefore, I developed the new multi-step synthesis shown below for these arginine analogues. As a test for their application in normal solid phase synthesis, I successfully prepared a tripeptide sequence Ala-AA1-Val (AA: arginine analogue. In a second project I studied the influence of additional ionic interactions within our binding motif. I synthesized a di-cationic and a tris-cationic receptor and evaluated the binding properties via NMR titration experiments against a variety of amino acids. Especially, the tris-cationic receptor was capable to strongly complex amino acids. The association constants were about a factor of 100 higher than those for the guanidiniocarbonyl pyrroles known so far. Even in 90 %water/10 % DMSO the association constants determined by NMR titration were extremely high with values around Kass = 2000 M-1. In the third project I developed a de-novo designed receptor for C-terminal dipeptides in a beta-sheet conformation based on molecular calculations. This receptor was studied in NMR and also UV titration experiments. In 40 % water/ 60 % DMSO the association constants were too strong to be measured by NMR titration experiments. Therefore, the complexation properties of 12 were studied by UV titration in water (with 10 % DMSO added for solubility reasons) with various dipeptides and amino acids as substrates. The data show that 12 binds dipeptides very efficiently even in water with association constants Kass > 10000 M-1, making 12 one of the most effective dipeptide receptors known so far. In contrast to that, simple amino acids are bound up to ten times less efficiently (Kass > 1000 M-1) than dipeptides. In the series of dipeptides studied the complex stability increases depending on the side chains present in the order Gly < Ala < Val which is a result of the decreasing flexibility of the peptide and the increasing hydrophobicity of the side chains. The binding properties of this receptor are superior to any other dipeptide receptor reported so far. Within my thesis I have not only developed an essential, mild and efficient synthetic approach for guanidiniocarbonyl pyrroles in general, but also a new binding motif for the complexation of amino acids 15, 11 and in addition a dipeptide receptor 12 that is superior to all dipeptides receptors known so far.
In the first part of this work we presented the synthesis and photophysical properties of a series of transition metal donor-acceptor Ir(III)complexes of the type [(C^N)2Ir(N^N)][PF6]. The Ir(III) was connected with hole conducting donor-moieties like carbazole (CZ) and triarylamine (TAA) linked via a methylene and ethylene bridge to the cyclometalating C^N ligands phenylpyrazole (ppz) and phenylpyridine (ppy). Bidentate N^N and P^P ligands like 2,2’-bipyridyl (bpy), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmp) and cis-1,2-bis(diphenylphosphino)ethylene (bdppe) were used as acceptor units. In order to analyse the influence of the electron density of the bpy ligand, TAA-complexes with acceptor- and donor-substituted bpy acceptor units were synthesised. Therefore, 4,4’-dinitro-2,2’-bipyridyl, 4,4’-dichloro-2,2’-bipyridyl, 4,4’-dimethoxy-2,2’-bipyridyl and 4,4’-dimethylamino-2,2’bipyridyl were used as neutral N^N ligands. In order to compare the photophysical properties, all reference compounds without hole conducting component were syntesised. All the carbazole compounds, except the bdppe complexes, exhibit emission and transient absorption properties similar to their reference compounds that make them interesting for OLED (organic light emitting device) applications. LEC (light emitting electrochemical cell) studies show a red shifted luminescence. The triarylamine compounds do not luminesce at RT but they exhibit an intense, blue-shifted and long-lived luminescence at 77 K in a rigid matrix. The transient absorption spectra differ strongly from that of their reference compounds. The spectra display characteristic features of the spectra of the isolated radical anions and cations supported by spectroelectrochemical measurements. Thus, it can be assumed that the transient states are charge separated (CS) states in which the positive charge is localised at the TAA donor units and the negative charge at the N^N acceptor units. The decays of the transient states are biexponentially what indicates the presence of two transient states, the 1CS and the 3CS state. To understand this behaviour the differently substituted bipyridyl-complexes were synthesised and analysed. Temperature dependent transient absorption measurements showed that all rate constants are indepentend of the temperature, except for the complex with OMe subsituents at the bpy ligand. The equilibrium constant K = k1 / k2 is nearly one for all complexes. For the OMe-compound it decreases with increasing temperature. Plotting the rate constants vs. the free energy differences (determined by cyclovoltammetry measurements) shows that all constants are decreasing with increasing donor strength of the bpy ligand. DFT calculations on the OMe-compound are already in work. In the second part of this work, neutral Ir(III) and Pt(II) complexes of the type [(O^O)Ir(N^N)2] and [(O^O)Pt(N^N)] were introduced. There, TTA was connected directly or via a CH2 bridge to acectylacetonate (acac = O^O) in order to probe the influence of the different kinds of connection on the photophysics of the complexes. As the bidentate N^N ligand 2,2’-bipyridyl (bpy) was chosen. All the corresponding reference compounds without triarylamine were obtained in order to compare with the TAA substituted analoga. Furthermore, the homoleptic fac Ir(N^N)3 complex with triarylamine connected via a methylene and ethylene bridge to phenylpyrazole as introduced in the first part of this work was synthesised. The synthesis of the Ir(III) compound with the TAA substituted acac ligand connected via the CH2 group was not successful. All the neutral triarylamine-substituted -diketonato Pt(II) and Ir(III) complexes do not luminesce at RT, except the Pt(II)-complex with CH2 bridge. This compound shows transient state characteristics that are in good agreement with the luminescence lifetimes at RT and that are similar to the reference compound, what suggests to a 3Pt(N^N)(O^O) state. The complexes without the CH2 bridging unit show no transient signals what may be caused by charge-transfer quenching due to the direct linkage between donor and acceptor unit. The homoleptic fac Ir(N^N)3 complex exhibits no emission at RT and no transient signals. At 77 K it shows a highly structured emission with 14 s lifetime. Compared to the literature-known reference compound this emission is caused by the population of a 3Ir(ppz)3 state. Our findings are important for designing complexes with stronger acceptor units (i.e. naphthaleneimide) for long CS states lifetimes to be used as photosynthesisers in solar cells and other optoelectronic devices. Besides, LEC and OLED studies on the carbazole complexes are still of interest to analyse the degree of triplet-triplet-annihiliation in these devices.
The self-assembly of molecules based on π-π-interactions and hydrogen bonding is of significant importance in nature. These processes enable the formation of complex supramolecular structures with diverse functions. For the transfer of the concepts from nature to artificial supramolecular structures, a basic understanding of those processes is needed. For this purpose, π-conjugated aromatic molecules with an easy synthetic access are suitable as their functionalities can be changed effortless. Perylene bisimide (PBIs) dyes are attractive candidates since they fulfill these requirements owing to their tendency to self-assemble in solution due to their large aromatic π-surfaces. Furthermore, the changes of the optical properties (for instance absorption, emission or circular dichroism) of PBI dyes, caused by their self-assembly, are easy to study experimentally. Structural variations of PBI dyes including additional non-covalent interactions, such as hydro-gen bonding, enable to direct their self-assembly process. Thus, the formation of interesting su-pramolecular structures of PBI dyes could be realized, although, often of undefined size. The aim of this thesis was to develop strategies to restrict the aggregate size of PBI dyes. Therefore, de-fined structural features of PBI molecules were combined and a variation of external influences such as solvent and concentration included. Furthermore, DNA was utilized as a template for the limitation of the aggregate size of PBI dyes.
Chapters 1 and 2 provide general information and describe examples from literature which are necessary to understand the following experimental work. The first chapter is based on the inter-actions of various molecules with DNA. Therefore, DNA is considered as a supramolecular biom-acromolecule containing specific structural and functional features to interact with small mole-cules. Afterwards, the main interaction modes of small molecules with DNA such as electrostatic interaction, intercalation and groove binding with corresponding examples are discussed. Among all techniques applied to study the interaction of ligands with DNA, UV/Vis absorption, fluores-cence and circular dichroism spectroscopy were described in detail. At the end of this chapter, examples of already pre-associated systems showing interactions with DNA are presented.
The second chapter is focused on the determination and mathematic evaluation of the self-assembly processes. The simplest models such as monomer-dimer and isodesmic model are de-scribed and supplemented by examples. Furthermore, the simplest modification of the isodesmic model, the K2-K model, is presented. Additionally, experimental problems, which may arise dur-ing the investigations of the self-assembly processes, are addressed. For the description of the entire self-assembly process, a sufficiently large concentration range and an appropriate measure-ment method that is sensitive in this concentration range is necessary. Furthermore, the full transi-tion from the monomeric to the aggregated species has to be spectroscopically ascertainable. This enables an accurate mathematic evaluation of the self-assembly process and provides meaningful binding constants. The self-assembly pathway can be controlled by the variation of solvent, con-centration or temperature. However, this pathway can also be directed by a rational design of the molecular structure of the considered system. For example, a specific interplay of π-π-interactions and hydrogen bonding may promote isodesmic as well as cooperative growth into large struc-tures.
The main focus of this thesis is to develop strategies to control the aggregate size of PBI dyes (Chapter 3). For this purpose, a PBI scaffold was designed which contains hydrogen bonding amide functions at the imide positions derived from the amino acid L-alanine and solubilizing side groups in the periphery (Figure 81). The variations of the residues R/R’ range from didodecylox-yphenyl, didodecylphenyl, dioligo(ethylene glycol)phenyl to branched and linear alkyl chains.
The most extensive study of the aggregation behavior was performed for the PBI dye 5. Concen-tration-dependent 1H NMR and UV/Vis absorption measurements clearly revealed the formation of dimers in chloroform. Further investigations by means of 2D NMR, VPO and ITC confirmed the exclusive presence of dimer aggregates of PBI 5 in the investigated concentration range. Mo-lecular modelling studies, supported by NMR and FT-IR experiments, provided structural reasons for the absence of further growth into larger aggregates. The specific combination of π-π interac-tions and hydrogen bonds between the NH groups of the amide groups and the carbonyl oxygen atoms of the PBI core are decisive for the formation of the discrete dimer stack (see Figure 82). The investigations of the aggregation behavior of PBIs 6-9 were less extensive but consistent with the results obtained for PBI 5. However, the determined binding constants vary over a considera-ble range of 1.1 x 102 M-1 (PBI 8) to 1.4 x 104 M-1 (PBI 5). These differences could be attributed to structural variations of the dyes. The electron-rich phenyl substituent promoted the aggregation tendency of PBIs 5-7 compared with 8 and 9 that carry only alkyl side chains. Thus, the π-π in-teractions of bay-unsubstituted PBI cores in combination with hydrogen bonding of the amide functions control the formation of discrete dimers of these PBI dyes.
The variation of conditions, such as solvent, change the aggregation behavior of PBI dyes. In the solvents toluene and/or methylcyclohexane, anti-cooperative growth into larger aggregates of PBI 5 was observed (Chapter 4). The important feature of this self-assembly process is the absence of isosbestic points over the whole concentration range in the UV/Vis absorption measurements. The preference for the dimeric species of PBI 5 remained in both solvents as well as in mixtures of them, but upon increasing the concentration these dimers self-assemble into larger aggregates.
An important feature of the self-assembly process is the preferred formation of even-numbered aggregates compared to the odd-numbered ones (see Figure 83). Although, the conventional K2-K model provides plausible binding constants, it is not capable to describe the aggregation behavior adequately, since it considers a continuous size distribution. The gradual aggregation process over dimers, tetramers, hexamers, etc. was therefore analyzed with a newly developed K2-K model for anti-cooperative supramolecular polymerization. By the global analysis of the UV/Vis absorption spectra a very good agreement between the experimental and simulated spectra, which were based on the new K2-K model, was obtained. Furthermore, the calculated UV/Vis absorption spectra of a dimer and an aggregate highlighted the most important structural differences. The absorption spectrum of the dimer still has a pronounced vibronic structure which gets lost in the spectrum of the aggregate.
In another part of this work, a series of water soluble PBI dyes were described which contain similar PBI scaffolds as PBIs 5-8 (Chapter 5). These PBI dyes self-assemble into similar dimer aggregates in water due to their positively charged side chains causing electrostatic repulsion be-tween the molecules (see Figure 84). Here, however, the self-assembly behavior has not been studied thoroughly in water due to the similarities of already reported PBI dyes.
Instead, the focus here is on the characterization of the interactions of these dyes with DNA/RNA. The comprehensive studies using thermal denaturation experiments showed the high stability of these PBI/polynucleotide complexes. The spermine-functionalized PBI dyes having six positive charges showed strong interactions with DNA/RNA which was expressed in a signif-icant increase of the melting temperatures of DNA/RNA (ΔTm values between 7 and > 35 ° C). The dioxa analogues containing only two positive charges had lower enhancement of the melting temperature of DNA/RNA (ΔTm values between 3 and 30 ° C). A similar trend has been observed in the fluorimetric titrations. The spermine-functionalized PBI dyes showed high binding con-stants (log Ks = 9.2 - 9.8), independently of the used polynucleotides. In contrast, the dioxa ana-logues displayed smaller binding constants (log Ks = 6.5 - 7.9) without any correlation between binding affinity and binding strength of the PBI dyes and the applied polynucleotides. The CD-spectroscopic measurements revealed significant differences in the binding properties of the dyes with DNA/RNA. They were dependent on the steric hindrance of the amino acid residues at the imide position and their configuration on one side and the grooves properties of ds-DNA/RNA on the other side. The spectroscopic results confirmed the formation of excitonically coupled PBI dimers in the minor groove of ds-DNA and the major groove of ds-RNA. Depending on the se-quence, the grooves of the polynucleotides provide different amount of space for embedding molecules. The guanine amino groups protrude into the minor groove of the polynucleotide poly(dG-dC)2 increasing the steric hindrance, which is not the case for poly(dA-dT)2. Molecular modeling studies showed that the PBI dimers penetrate deeper into the groove of poly(dA-dT)2 due to the absence of the steric hindrance, in comparison to the groove of poly(dG-dC)2 (see Figure 85).
Paclitaxel (PTX) is one of the leading drugs against breast and ovarian cancer. Due to its low solubility, treatment of the patients with this drug requires a very well-suited combination with a soluble pharmaceutical excipient to increase the bioavailability and reduce the strong side ef-fects. One efficient way to achieve this in the future could be the incorporation of PTX into pol-ymeric micelles composed of poly(2-oxazoline) based triblock copolymers (POL) which ena-bles PTX loadings of up to 50 wt.%. However, structural information at an atomic level and thus the knowledge of interaction sites within these promising but complex PTX-POL formula-tions were not yet available. Such results could support the future development of improved excipients for PTX and suitable excipients for other pharmaceutical drugs. Therefore, a solid-state MAS NMR investigation of these amorphous formulations with different POL-PTX com-positions was performed in this thesis as this gives insights of the local structure at an atomic level in its solid state. NMR in solution showed very broad 13C signals of PTX for this system due to the reduced mobility of the incorporated drug which exclude this as an analytical meth-od.
In a first study, crystalline PTX was structurally characterized by solid-state NMR as no com-plete 13C spectrum assignment and no 1H NMR data existed for the solid state. In addition, the asymmetric unit of the PTX crystal structure consists of two molecules (Z'=2) that can only be investigated in its solid state. As crystalline PTX in total has about 100 different 13C and 1H chemical shifts with very small differences due to Z’=2, and furthermore, its unit cell consisting of more than 900 atoms, accompanying GIPAW (CASTEP) calculations were required for NMR signal assignments. These calculations were performed using the first three available purely hydrous and anhydrous PTX structures, which were determined by XRD and published by Vel-la-Zarb et al. in 2013. Within this thesis, is was discovered that two investigated batches of commercially available PTX from the same supplier both contained an identical and so far un-known PTX phase that was elucidated by PXRD as well as solid-state NMR data. One of the two batches consists of an additional phase that was shown to be very similar to a known hy-drated phase published in 2013.[1] By heating the batch with the mixture of the two phases un-der vacuum, it is transformed completely to the new dry phase occurring in both PTX batches. Since the drying conditions to obtain anhydrous PTX in-situ on the PXRD setup described by Vella-Zarb et. al.[1] were much softer than ours, we identify our dry phase as a relaxed version of their published anhydrate structure. The PXRD data of the new anhydrate phase was trans-ferred into a new structural model, which currently undergoes geometry optimization. Based on solid-state NMR data at MAS spinning frequencies up to 100 kHz, a 13C and a partial 1H signal assignment for the new anhydrous structure were achieved. These results provided sufficient structural information for further investigations of the micellar POL-PTX system.
In a second study, the applicability and benefit of two-dimensional solid-state 14N-1H HMQC MAS NMR spectra for the characterization of amorphous POL-PTX formulations was investi-gated. The mentioned technique has never been applied to a system of similar complexity be-fore and was chosen because around 84% of the small-molecule drugs contain at least one nitrogen atom. In addition, the number of nitrogen atoms in both POL and PTX is much smaller than the number of carbons or hydrogens, which significantly reduces the spectral complexity. 14N has a natural abundance of 99.6% but leads to quadrupolar broadening due to its nuclear spin quantum number I = 1. While this is usually undesirable due to broadening in the resulting 1D 14N NMR spectra, this effect is explicitly used in the 2D 14N-1H HMQC MAS experiment. The indirect 14N measurement can avoid the broadening while maintaining the advantage of the high natural abundance and making use of the much more dispersed signals due to the additional quadrupolar shifts as compared to 15N.
This measurement method could be successfully applied to the complex amorphous POL-PTX mixtures. With increasing PTX loading of the formulations, additional peaks arise as spatial proximities of the amide nitrogens of POL to NH or OH groups of PTX. In addition, the 14N quadrupolar shift of these amide nitrogens decreases with increasing PTX content indicating a more symmetric nitrogen environment. The latter can be explained by a transformation of the trigonal planar coordination of the tertiary amide nitrogen atoms in pure POL towards a more tetrahedral environment upon PTX loading induced by the formation of hydrogen bonds with NH/OH groups of PTX.
In the third and last project, the results of the two abovementioned studies were used and ex-tended by solid state 13C and two-dimensional 1H-13C as well as 1H-1H MAS NMR data with the aim to derive a structural model of the POL-PTX formulations at an atomic level. The knowledge of the NMR signal assignments for crystalline PTX was transferred to amorphous PTX (present in the micelles of the formulations). The 13C solid-state NMR signals were evalu-ated concerning changes in chemical shifts and full widths of half maximum (FWHM) for the different PTX loadings. In this way, the required information about possible interaction sites at an atomic level becomes available. Due to the complexity of these systems, such proximities often cannot be assigned to special atoms, but more to groups of atoms, as the individual de-velopments of line widths and line shifts are mutually dependent. An advantageous aspect for this analysis was that pure POL already forms unloaded micelles. The evaluation of the data showed that the terminal phenyl groups of PTX seem to be most involved in the interaction by the establishment of the micelle for lowest drug loading and that they are likely to react to the change in the amount of PTX molecules as well. For the incorporation of PTX in the micelles, the following model could be obtained: For lowest drug loading, PTX is mainly located in the inner part of the micelles. Upon further increasing of the loading, it progressively extends to-ward the micellar shell. This could be well shown by the increasing interactions of the hydro-phobic butyl chain of POL and PTX, proceeding in the direction of the polymer backbone with rising drug load. Furthermore, due to the size of PTX and the hydrodynamic radius of the mi-celles, even at the lowest loading, the PTX molecules partially reach the core-shell interface of the micelle. Upon increasing the drug loading, the surface coverage with PTX clusters increas-es based on the obtained model approach. The latter result is supported by DLS and SANS data of this system. The abovementioned results of the 14N-1H HMQC MAS investigation of the POL-PTX formulations support the outlined model.
As an outlook, the currently running geometry optimization and subsequently scheduled calcu-lation of the chemical shieldings of the newly obtained anhydrous PTX crystal structure can further improve the solid-state NMR characterization through determination of further spatial proximities among protons using the existing 2D 1H(DQ)-1H(SQ) solid-state MAS NMR spec-trum at 100 kHz rotor spinning frequency. The 2D 14N-1H HMQC MAS NMR experiments were shown to have great potential as a technique for the analysis of other disordered and amor-phous drug delivery systems as well. The results of this thesis should be subsequently applied to other micellar systems with varying pharmaceutical excipients or active ingredients with the goal of systematically achieving higher drug loadings (e.g., for the investigated PTX, the similar drug docetaxel or even different natural products). Additionally, it is planned to transfer the knowledge to another complex polymer system containing poly(amino acids) which offers hy-drogen bonding donor sites for additional intermolecular interactions. Currently, the POL-PTX system is investigated by further SANS studies that may provide another puzzle piece to the model as complementary measurement method in the future. In addition, the use of MD simu-lations might be considered in the future. This would allow a computerized linking of the differ-ent pieces of information with the aim to determine the most likely model.
In summary, it can be stated that the herein studied set of acceptor-substituted squaraine dyes can be seen as potent candidates for OTFTs. Furthermore, their transistor performance can be easily tuned to obtain hole mobilities up to 0.45 cm2/Vs from solution and 1.3 cm2/Vs from sublimation by choosing adequate deposition techniques. In the end, a probable structural model derived from studies of the thin-film morphology by methods such as optical spectroscopy, AFM and X-ray even facilitated the clarification of the observed charge transport behavior.
This thesis established the fabrication of organic solar cells of DA dye donors and fullerene acceptors under ambient conditions in our laboratory, however, with reduced power conversion efficiencies compared to inert conditions. It was shown that moisture had the strongest impact on the stability and reproducibility of the solar cells. Therefore, utilization of robust materials, inverted device architectures and fast fabrication/characterization are recommended if processing takes place in air. Furthermore, the dyad concept was successfully explored in merocyanine dye-fullerene dyads and power conversion efficiencies of up to 1.14 % and 1.59 % were measured under ambient and inert conditions, respectively. It was determined that the major drawback in comparison to comparable BHJ devices was the inability of the dyad molecules to undergo phase separation. Finally, two series of small molecules were designed in order to obtain electron transport materials, using the acceptor-core-acceptor motive. By variation of the acceptor units especially the LUMO levels could be lowered effectively. Investigation of the compounds in organic thin film transistors helped to identify promising molecules with electron transport properties. Electron transport mobilities of up to 7.3 × 10−2 cm2 V−1 s−1 (ADA2b) and 1.39 × 10−2 cm2 V−1 s−1 (AπA1b) were measured in air for the ADA and AπA dyes, respectively. Investigation of selected molecules in organic solar cells proved that these molecules work as active layer components, even though power conversion efficiencies cannot compete with fullerene based devices yet. Thus, this thesis shows new possibilities that might help to develop and design small molecules as substitutes for fullerene acceptors.
The research presented in this thesis illustrates that self-assembly of organic molecules guided by intermolecular forces is a versatile bottom-up approach towards functional materials. Through the specific design of the monomers, supramolecular architectures with distinct spatial arrangement of the individual building blocks can be realized. Particularly intriguing materials can be achieved when applying the supramolecular approach to molecules forming liquid-crystalline phases as these arrange in ordered, yet mobile structures. Therefore, they exhibit anisotropic properties on a macroscopic level. It is pivotal to precisely control the interchromophoric arrangement as functions originate in the complex structures that are formed upon self-assembly. Consequently, the aim of this thesis was the synthesis and characterization of liquid-crystalline phases with defined supramolecular arrangements as well as the investigation of the structure-property relationship. For this purpose, perylene bisimide and diketopyrrolopyrrole chromophores were used as they constitute ideal building blocks towards functional supramolecular materials due to their thermal stability, lightfastness, as well as excellent optical and electronic features desirable for the application in, e.g., organic electronics.
Summary The nature of the chemical bond is a topic under constant debate. What is known about individual molecular properties and functional groups is often taught and rationalized by explaining Lewis structures, which, in turn, make extensive use of the valence concept. The valence concept distinguishes between electrons, which do not participate in chemical interactions (core electrons) and those, which do (single, double, triple bonds, lone-pair electrons, etc.). Additionally, individual electrons are assigned to atomic centers. The valence concept is of paramount success: It allows the successful planning of chemical syntheses and analyses, it explains the behavior of individual functional groups, and, moreover, it provides the “language” to think of and talk about molecular structure and chemical interactions. The resounding success of the valence concept may be misleading to forget its approximative character. On the other hand, quantum mechanics provide in principle a quantitative description of all chemical phenomena, but there is no discrimination between electrons in quantum mechanics. From the quantum mechanical point of view there are only indistinguishable electrons in the field of the nuclei, i.e., it is impossible to assign a given electron to a particular center or to ascribe a particular purpose to individual electrons. The concept of indistinguishability of micro particles is founded on the Heisenberg uncertainty relation, which states, that wavepackets diverge in the 6N dimensional phase space, such that individual trajectories can not be identified. Hence it is a deep-rooted and approved physical concept. As an introduction to the present work density partitioning schemes were discussed, which divide the total molecular density into chemically meaningful areas. These partitioning schemes are intimately related to either the concepts of bound atoms in a molecule (as in the Atoms In Molecules theory (AIM) according to Bader or as in the Hirshfeld partitioning scheme) or to the concept of chemical structure in the sense of Lewis structures, which divide the total molecular density into core and valence density, where the valence density is split up again into bonding and non-bonding electron densities. Examples are early and recent loge theories, the topological analysis by means of the Electron Localization Function (ELF), and the Natural Bond Orbital (NBO) approach. Of these partitioning schemes, the theories according to Bader (AIM), to Becke and Edgecomb (ELF) and according to Weinhold (NBO and Natural Resonance Theory, NRT), respectively, were reviewed in detail critically. Points of criticism were explicated for each of the mentioned theories. Since theoretically derived electron densities are to be compared to experimentally derived densities, a brief introduction into the theory of X-ray di®raction experiments was given and the multipole formalism was introduced. The procedure of density refinement was briefly discussed. Various suggestions for improvements were developed: One strategy would be the employment of model parameters, which are to a maximum degree mutually orthogonal, with the object of minimizing correlations among the model parameters, e.g., to introduce nodal planes into the radial functions of the multipole model. A further suggestion involves the guidance of the iterative refinement procedure by an extremum principle, which states, that when di®erent solutions to the least squares minimization problem are available with about the same statistical measures of quality and with about the same residual density, then the solution is to prefer, which yields a minimum density at the bond critical point (BCP) and a maximum polarity in terms of the ratio of distances between the BCP and the nuclei. This suggestion is based on the well known fact, that the bond polarity (in terms of the ratio of distances between the BCP and the respective nuclei) is underestimated in the experiment. Another suggestion for including physical constraints is the explicit consideration of the virial theorem, e.g., by evaluating the integration of the Laplacian over the entire atomic basins and comparing this value to zero and to the value obtained from the integration of the electron gradient field over the atomic surface. The next suggestion was to explicitly use the electrostatic theorem of Feynman (often also denoted as Hellmann-Feynman theorem), which states, that the forces onto the nuclei can be calculated from the purely classical electrostatic forces of the electron distribution and the nuclei distribution. For a stationary system, these forces must add to zero. This also provides an internal quality criterion of the density model. This can be performed in an iterative way during the refinement procedure or as a test of the final result. The use of the electrostatic theorem is expected to reduce significantly correlations among static density parameters and parameters describing vibrations, since it is a valuable tool to discriminate between physically reasonable and artificial static electron densities. All of these mentioned suggestions can be applied as internal quality criteria. The last suggestion is based on the idea to initiate the experimental refinement with a set of model parameters, which is, as much as possible close to the final solution. This can be achieved by performing periodic boundary conditions calculations, from which theoretically created files are obtained, which contain the Miller indices (h, k, l) and the respective intensity I. This file is used for a model parameter estimation (refinement), which excludes vibrations. The resulting parameters can be used for the experimental refinement, where, in a first step, the density parameters are fixed to determine the parameters describing vibrations. For a fine tuning, again the electrostatic theorem and the other above mentioned suggestions could be applied. Theoretical predictions should not be biased by the method of computation. Therefore the dependence of the density analyzing tools on the level of calculation (method of calculation/basis set) and on the substituents in complex chemical bonding situations were evaluated in the second part of the present work. A number of compounds containing formal single and double sulfur nitrogen bonds was investigated. For these compounds, experimental data were also available. The calculated data were compared internally and with the experimental results. The internal comparison was drawn with regard to questions of convergency as well as with regard to questions of consistency: The resulting molecular properties from NBO/NRT analyses were found to be very stable, when the geometries were optimized at the respective level of theory. This stability is valid for variations in the methods of calculation as well as for variations in the basis set. Only the individual resonance weights of the contributing Natural Lewis Structures differed considerably depending on the level of calculation and depending on the substituents. However, the deviations were in both cases to a large extent within a limit which preserves the descending order of the leading resonance structure weights. The resulting bond orders, i.e., the total, covalent and ionic bond order from NRT calculations, were not affected by the shift in the resonance weights. The analysis of the bond topological parameters resulted in a discrimination between insensitive parameters and sensitive parameters. The stable parameters do neither depend strongly on the method of calculation nor on the basis set. Only minor variation occurs in the numerical values of these parameters, when the level of calculation is changed or even when other functional groups (H, Me, or tBu) are employed, as long as the methods of calculation do not drop considerably below a standard level. The bond descriptors of the sulfur nitrogen bonds were found to be also stable with respect to the functional groups R = H, R = Me, and R = tBu. Stable parameters are the bond distance, the density at the bond critical point (BCP) and the ratio of distances between the BCP and the nuclei A and B, which varies clearly when considering the formal bond type. For very small basis sets like the 3-21G basis set, this characteristic stability collapses. The sensitive parameters are based on the second derivatives of the density with respect to the coordinates. This is in accordance with the well known fact, that the total second derivative of the density with respect to the coordinates is a strongly oscillating function with positive as well as negative values. A profound deviation has to be anticipated as a consequence of strong oscillations. lambda3, which describes the local charge depletion in the direction of the interaction line, is the most varying parameter. A detailed analysis revealed that the position of the BCP in the rampant edge of the Laplacian distribution is responsible for the sensitivity of the numerical value of lambda3 in formal double bonds. Since the slope of the Laplacian assumes very high values in its rampant edge, a tiny displacement of the BCP leads already to a considerable change in lambda3. This instability is not a failure of the underlying theory, but it yields de facto to a considerable dependence of sensitive bond topological properties on the method of calculation and on the applied basis sets. Since the total second derivative is important to judge on the nature of the bond in the AIM theory (closed shell interactions versus shared interactions), the changes in lambda3 can lead to differing chemical interpretations. The comparison of theoretically derived bond topological properties of various sulfur nitrogen bonds provides the possibility to measure the self consistency of this data set. All data sets clearly exhibit a linear correlation between the bond distances and the density at the BCP on one hand and between the bond distances and the Laplacian values at the BCP on the other hand. These correlations were almost independent of the basis set size. In this context, the linear regression has to be regarded exclusively as a descriptive statistics tool. There is no correlation anticipated a priori. The formal bond type was found to be readily deducible from the theoretically obtained bond topological descriptors of the model systems. In this sense, the bond topological properties are self consistent despite of the numerical sensitivity of the derivatives, as exemplified above. Often, calculations are performed with the experimentally derived equilibrium geometries and not with optimized ones. Applying this approach, the computationally costly geometry optimizations are saved. Following this approach the bond topological properties were calculated using very flexible basis sets and employing the fixed experimental geometry (which, of course, includes the application of tBu groups). Regression coe±cients similar to those from optimized geometries were obtained for correlations between bond distances and the densities at the BCP as well as for the correlation between bond distances and the Laplacian at the BCP, i.e. the approach is valid. However, the data points scattered less and the coe±cient of correlation was clearly increased when geometry optimizations were performed beforehand. The comparison between data obtained from theory and experiment revealed fundamental discrepancies: In the data set of bond topological parameters from the experiment, the behavior of only 2 out of 3 insensitive parameters was comparable to the behavior of the theoretically obtained values, i.e. theoretical and experimental bond distances as well as theoretical and experimental densities at the BCP correlate. From the theoretically obtained data it was easy to deduce the formal bond type from the position of the BCP, since it changed in a systematic manner. The respective experimentally obtained values were almost constant and did not change systematically. For the SN bonds containing compounds, the total second derivative assumes exclusively negative values in the experiment. Due to the different internal behavior, experimentally and theoretically sensitive bond topological values could not be compared directly. The qualitative agreement in the Laplacian distribution, however, was excellent. In the third and last part of this work, the application to chemical systems follows. Formal hypervalent molecules, i.e. molecules where some atoms are considered to hold more than 8 electrons in their valence shell, were investigated. These were compounds containing sulfur nitrogen bonds (H(NtBu)2SMe, H2C{S(NtBu)2(NHtBu)}2, S(NtBu)2 and S(NtBu)3) and a highly coordinated silicon compound. The set of sulfur nitrogen compounds also contained a textbook example for valence expansion, the sulfur triimide. For these molecules, experimental reference values were available from high resolution X-ray experiments. The experimental results were in the case of the sulfur triimide not unique. Furthermore, from the experimental bond topological data no definite conclusion about the formal bonding type could be drawn. The situation of sulfur nitrogen bonds in the above mentioned set of molecules was analyzed in terms of a geometry discussion and by means of a topological analysis. The methyl-substituted isolated molecules served as model compounds. For the interpretation of the bonding situation additional NBO/NRT calculations were preformed for the sulfur nitrogen compounds and an ELF calculation and analysis was performed for the silicon compound. The ELF analysis included not only the presentation and discussion of the ELF-isosurfaces (eta = 0.85), but also the investigation of populations of disynaptic valence basins and the percentage contributions to these populations of the individual atoms when the disynaptic valence basins are split into atomic contributions according to Bader’s partitioning scheme. The question of chemical interest was whether hypervalency is present in the set of molecules or not. In the first case the octet rule would be violated, in the second case Pauling’s verdict would be violated. While the concept of hypervalency is well established in chemistry, the violation of Pauling’s verdict is not. The quantitative numbers of the sensitive bond topological values from theory and experiment were not comparable, since no systematic relationship between the experimentally and theoretically determined sensitive bond descriptors was found. However, the insensitive parameters are in good agreement and the qualitative Laplacian distribution is, with few exceptions, in excellent agreement. The formal bonding type was deduced from experimental and theoretical topological data by considering the number and shape of valence shell charge concentrations in proximity to the sulfur and nitrogen centers. The results from NBO/NRT calculations confirmed the findings. All employed density analyzing tools AIM, ELF and NBO/NRT coincided in describing the bonding situation in the formally hypervalent molecules as highly polar. A comparison and analysis of experimentally and theoretically derived electron densities led consistently to the result, that regarding this set of molecules, hypervalency has to be excluded unequivocally.
Thus, the main focus of this thesis was to generate and investigate new one-dimensional LC PBI J-aggregates of an entirely new PBI organization with the transition dipole moments of the chromophores arranged parallel to the columnar axis and in slipped pi-pi stacking fashion to form highly fluorescent J-aggregates. Towards this goal, the tetra-bay substituted PBI 4c bearing free NH functional groups at the imide positions and four dendrons with branched ethylhexyl alkoxy chains at the meta-position of the phenoxy spacer (Figure 8.1a) was synthesized and compared to a literature known reference PBI 1. The mesogenic dendrons ensure LC character of the dye, which was confirmed by POM, DSC and extensive X-ray analysis. Furthermore, the sterically demanding bay-substituents prevent the cofacial assembly of the chromophores and force the dyes into a slipped pi-stacked order with the main transition dipole moments of the dyes oriented parallel to the columnar axis. X-ray analysis revealed that PBI 4c assembles into columnar triple-stranded helices consisting of side-to-side stacked molecules, which organize into a Colh phase (Figure 8.1b). FT-IR experiments of a thin film and aggregates in MCH solution confirmed the formation of H-bonds between the imide moieties. Temperature-dependent investigations furthermore proved a reversible formation of H-bonds and polarized FT-IR experiments finally gave evidence for the direction of the H-bonds along the shearing respective the columnar axis (Figure 8.1c). This was additionally verified by polarized UV-Vis absorption studies of aligned thin films. The changes in the UV-Vis absorption spectra of concentration- and temperature-dependent experiments in MCH are in agreement with the formation of J-aggregates and could be fitted to a nucleation-elongation growth mechanism. Remarkably, fluorescence spectroscopy studies revealed highly emissive aggregates in solution. These various spectroscopic techniques proved the utilization of directional noncovalent forces like hydrogen-bonding and pi-pi interactions in a cooperative manner forcing the PBI molecules in an unprecedented organization of a slipped pi-stacked arrangement with the orientation of the molecular axis and the respective transition dipole moments parallel to the columns of the LC phase. By the group of Dietrich the formation of exciton-polaritons in imprinted LC pillar microcavities as consequent use of the LC 4c was reported for the first time.In the second part of this thesis the hierarchical organization of LC PBIs into defined single-, double-, triple- and quadruple-stranded J-aggregates within crystalline and columnar LC phases, partially arranged in helical supramolecular structures in dependence of the molecular design was demonstrated. This was achieved via the preparation of a library of twelve molecules PBI 3-6(a-c) (Figure 8.2a) that was synthesized by varying the substitution position of the dendrons at the phenoxy-spacer from ortho to meta or para and by introducing an additional methyl group in ortho-position. Also the length and shape of the alkoxy chains was changed. Consequently, the impact of the sterical demand of the bay substituents concerning their phase properties, molecular arrangement and exciton coupling was investigated. POM, DSC and X-ray studies revealed the formation of only crystalline phase for the ortho-substituted PBIs 3a-c, whereas the other derivatives generated SC or LC phases. The main focus was the series with the n-C12-alkoxy chains. For the corresponding PBIs 4-6b columnar LC phases were confirmed. Retrostructural analysis by modelling and simulations gave indications for a single stranded organization for PBI 3b, a double-stranded helix for PBI 6b, a triple-stranded helical arrangement for PBI 5b and a quadruple-stranded helix for PBI 4b (Figure 8.2b-d). For all four derivatives the same molecular orientation within the columns as for PBI 4c was proven by polarized FT-IR and UV-Vis absorption studies in aligned thin films. The organization in helices of different number of strands in the Cr and LC phases of PBI 3b, 4b, 5b and 6b offered a unique possibility to elucidate the influence of particular packing arrangements on dye aggregate interactions with light. In particular, it can be investigated how exciton coupling of the dyes’ transition dipole moments and fluorescence properties are affected. In this context, the spectroscopic properties were investigated in thin film, which revealed a strong bathochromic shift of the absorption maxima compared to the monomers in solution in dependence on the number of strands for PBIs 4-6b in contrast to PBI 3b (Figure 8.2e). The same tendency was observed for the respective aggregates in MCH solution. The spectral changes obtained during concentration- and temperature-dependent UV-Vis absorption studies verified the formation of J-aggregates in MCH solution and solid state. The respective aggregates are highly likely formed via a nucleation-elongation growth mechanism. Appliance of Kasha’s exciton theory on the supramolecular aggregates revealed different contributions of H- and J-type coupling for the oligo-stranded helices. Under these considerations, it delivered an explanation for the absorption and fluorescence properties of the assemblies and declares the “best” J-aggregate for the double stranded arrangement of PBI 6b with purely negative couplings among neighbour molecules and a quantum yield above 74 % of the aggregates in MCH solution. With this H-bonded PBI-based library approach of twelve derivatives it could be shown how molecular engineering of perylene bisimide dyes can be used to design defined, complex supramolecular assemblies with unprecedented packing patterns and concomitant intriguing spectroscopic properties.
So far, the formation of defined liquid crystalline supramolecular structures of tetra-bay substituted PBIs by double H-bonding between free imide moieties and pi-pi interactions between the chromophores was demonstrated. The impact of the H-bonds on the molecular arrangement was investigated in the next part of this thesis. In this regard, PBIs 7 and 8 bearing a methyl or cyclohexyl group at the imide position (Figure 8.3a) were synthesized and compared to PBI 4c. The soft character of the solid state for PBIs 7 and 8 was confirmed by POM, DSC and X-ray analysis. The X-ray studies further revealed for both PBIs a change of the molecular assembly towards helical columnar structures of conventional pi-stacked chromophores (Figure 8.3b) when the directed H-bonds cannot contribute as noncovalent interactions to the assembly formation. Temperature-dependent UV-Vis absorption studies demonstrated the importance of H-bonding in MCH solution in the way that the formation of J-aggregates as for PBI 4c could not be observed for the imide substituted molecules. In the next step, the spectroscopic properties in thin film were investigated. For PBI 7 a J-type band and fluorescence spectra with an enlarged Stokes shift and increased fluorescence lifetime of 11.4 ns, compared to PBI 4c, was obtained, suggesting the generation of excimer type emission by considering the assumed conventional stacking of rotational displaced molecules from X-ray analysis. With polarized UV-Vis absorption experiments the orientation of the molecules perpendicular to the shearing direction and subsequently to the columnar axis was confirmed. These diverse investigations clearly demonstrated the imperative of H-bonds for stable, defined, LC J-aggregates with the transition dipole moments parallel to the columnar axis. With PBIs 7 and 8 it is impressively shown how small changes in the molecular structure influence the molecular arrangement dependent on the cooperation of non-covalent interactions like H-bonding and pi-pi stacking.
In the last part of this thesis the generation of two-dimensional LC arrangements is presented. Since tetra-bay substituted PBIs lead always to twisted cores preventing lamellar arrangement, here 1,7-disubstitution and the simultaneous retention of the free imide positions was chosen to generate LC lamellar phases of PBIs 9a, 9b and 10 (Figure 8.4a). This molecular design was expected to form planar perylene cores that can strongly interact by pi-pi stacking and H-bonding. POM, DSC and X-ray investigations of the compounds suggest lamellar LC phases for PBIs 9a and 9b and a soft phase for PBI 10. In this regard, the goal of the formation of LC lamellar phase of PBIs could be attained. The change from dendrons with n-C12-alkoxy chains to large fork-like mesogens like in 9b clearly changed the phase properties. PBI 9b exhibits the lowest clearing point, high phase stability, least viscosity, easy shearability at room temperature and phase transitions between lamellar and Colh phases dependent on temperature. The formation of H-bonds parallel to the layers was demonstrated by polarized FT-IR experiments for all three PBIs. Concentration-dependent UV-Vis absorption studies revealed the formation of a J-type aggregate, which seems to exhibit an overall two-dimensional structure. With STM investigations the formation of lamellar structures from drop-casted 9a and 10 solutions in 1-phenyloctane on HOPG surface could be observed. Figure 8.4b illustrates a schematic possible arrangement of the molecules in the layers (here exemplarily demonstrated for PBI 9a), which has to be further confirmed by modelling and simulations. Unfortunately, fluorescence investigations of the thin films revealed non- or only slightly emissive LC states, which make them negligible for photonic applications. Nevertheless, the synthesized and analyzed compounds might be an inspiration for further investigations on the path to two-dimensional exciton transport for photonic devices.
The present work deals with the synthesis and the investigation of the photophysical properties of covalently constructed calix[4]arene–perylene bisimide dye arrays containing various PBI units. The obtained conjugates are characterized with respect towards their application in a new, zigzag-type architecture of artificial light-harvesting systems. For this purpose, orange (core-unsubstituted), red (6,7,11,12-tert-butylphenoxy-functionalized) and green (1,7-pyrrolidino-substituted) perylene bisimide building blocks have been attached to the calix[4]arene scaffold. First, the monochromophoric reference systems have been studied, and second, the photophysical properties of a comprehensive series of newly synthesized, multichromophoric calix[4]arene–perylene bisimide conjugates showing efficient energy transfer processes between the individual dye subunits have been investigated. Furthermore, a series of bichromophoric compounds containing identical chromophoric units has been obtained. Towards this goal, a variety of spectroscopic techniques such as UV/vis absorption, steady state and time-resolved fluorescence emission, and femtosecond transient absorption spectroscopy as well as a spectrotemporal analysis of the obtained data has been applied. This work presents a new concept for an artificial light-harvesting system positioning the dye units by means of calix[4]arene spacers along a zigzag chain. The investigations start with the syntheses and optical properties of the monochromophoric building blocks and result in an elaborate study on the energy and electron transfer processes occurring after photoexcitation in a comprehensive series of multichromophoric calix[4]arene–perylene bisimide conjugates. Finally, the photophysical properties of a series of compounds containing each two identical PBI units are discussed.
In the first part of this work a new approach to measure transient absorption spectra of fluorescent compounds by means of laser flash photolysis technique was presented. Generally, the recorded transient absorption signal consists of transient absorption, fluorescence and ground state bleaching. Thus, for fluorescent chromophores a fluorescence correction is indispensable in order to obtain undisturbed absorption decay curves as well as accurate transient absorption spectra. Due to time response characteristics of the PMT detector the fluorescence contribution cannot be corrected by recording the fluorescence separately. Measuring two transient absorption signals with probe light differing in intensity, compounds with quantum yields up to ~ 35 % can be investigated. This is a major improvement because transient absorption spectroscopy is a powerful method to gain insight into the kinetics and the energy of excited states and information in the time domain of fluorescence are no longer lost. In the second part the synthesis and the photophysical characterisation of redox cascades were reported. These cascades consist of an acridine acceptor and up to three triarylamine donor subunits. The redox potentials of the triarylamines were tuned by adequate substituents in the para-position of the phenyl ring to ensure a directed redox gradient. Upon photoexcitation a locally excited state or a CT state is populated which then injects a hole onto the adjacent donor and consequently results in a CS state. Fluorescence and transient absorption measurements revealed that HT depends strongly on donor strength and solvent polarity. Formation of a CS state was only observed in case of strong terminal donors or polar solvents. A low lying localised triplet state acts as an energy trap and quenches all CS states even in case of the cascade with the strongest terminal donor in very polar solvents. Furthermore, population of a CS state catalyses the formation of this triplet states which results in a shorter lifetime of the CS state compared to the lifetime of the CT state of the corresponding reference compound. Compared to redox cascades already reported in literature, the electronic coupling between the redox centres was decreased by sterical as well as electronic effects. To prolong the lifetime of the CS state saturated spacers on the one hand and a perpendicular orientation of the acceptor and the adjacent donor on the other hand were selected. The twisting of the subunits forming the CT state results in a higher degree of charge separation but its contribution to increase the lifetimes of the CS states is of minor importance. The longer lifetime of the CS states can be ascribed to the saturated spacers. Experimental data in combination with calculated values indicate that charge recombination takes place in the Marcus normal region by a superexchange mechanisms. Although charge recombination of the known cascades is located in the Marcus inverted region, these CS states decay faster than the CS states of the compounds investigated in this work.
The present work consists of two parts. The first one deals with theoretical questions and tests the performance of orbitals obtained from a self-interaction free KS method, the LHFapproach, in multireference ab initio methods. The purpose of this part is to enable a more efficient computation of excitation energies, which is important for the spectroscopic characterization of many organic and bioorganic molecules. The second part focuses on bioorganic questions and studies the base pairing properties of the purine base xanthine in order to explain, e.g., the unusually high stability of selfpairing xanthine alanyl-PNA double strands and the mutagenicity of xanthine formed in DNA. Part1: In contrast to HF- and standard DFT-methods, the LHF-approach leads to a fully bound virtual orbital spectrum, because Coulomb self interactions are exactly canceled in the LHFansatz. Furthermore, the energies of the occupied orbitals are not upshifted, like it is the case for standard DFT-methods, so that Koopmans' theorem remains valid. In line with this, also the occupied LHF-orbitals are somewhat more compact than standard DFT-orbitals. The present work shows that both properties are of great benefit for MR methods. The virtual LHF-orbitals are well optimized and allow an efficient description of excited states and static correlation in both MRCI- and MRPT2-approaches. Furthermore, the higher compactness of the occupied LHF- compared to standard DFT-orbitals leads to a better description of the center ion of Rydberg states. However, for each of the two advantages mentioned at least one example molecule has been found, for which LHF-orbitals actually perform worse than HF-and/or standard DFT-orbitals. This shows, that even though LHF virtual orbitals allow an excellent MRCI- and MRPT2-description for the electronically excited states of a large number of molecules, this cannot be generalized and their performance needs to be tested for each individual case. In the second part of the present work, the base pairing properties of xanthine and xanthine derivatives were studied. The purpose of this part was to find an explanation for the unexpectedly high stability of the xanthine alanyl PNA double strand. Furthermore, it was analyzed, why xanthine, that is formed from guanine in DNA under chemical stress, is able to form mismatched base pairs with the pyrimidine base thymine. Stability of xanthine alanyl PNA: In the first step, the regioisomer present in the considered alanyl PNA was identified to be the N7-regioisomer of xanthine by a theoretical analysis of the 13C-NMR spectrum. To analyze the stability of the xanthine self-pairing, a simplified model was set up, in which the stability of the PNA double strand was explained solely by the energy contributions from H-bonding and base stacking. For that purpose, the dimerization and stacking energies for the xanthine-xanthine, guaninecytosine, adenine-thymine and xanthine-2,6-diaminopurine base pairs were computed using DFT and MP2 methods. Solvent effects were taken into account by the conductor like screening model. The influence of the peptide backbone on the stacking geometry was considered by force field optimizations. While the individual contributions from hydrogen bonding and stacking do not correlate with the melting temperature Tm, the sum of both correlates linearly with Tm. This correlation is somewhat surprising, because this means that the effects of the entropy and the molecular water environment either cancel or are similar for all systems compared. In this model, the stability of the xanthine selfpairing mainly stems from an enlarged stacking interaction, while the H-bonds give only minor contributions to the stability of the xanthine selfpaired double strand of alanyl-PNA. Base pairing properties of N9-Xanthine: The computation of the base pairing properties of N9-xanthine revealed a strong variation in the individual H-bond strengths for the selfpairing of xanthine, that range from -4 to -11 kcal/mol in the gas phase and -2.5 to -5 kcal/mol in polar solvent. By comparison with model systems it was shown that the strong variance of the H-bond strength is mainly due to attractive or repulsive secondary electrostatic interactions. For the homodimer of hypoxanthine it was shown that the increase of aromaticity in the pyrimidine ring upon dimer formation leads to a strengthening of the hydrogen bonds. Mutagenicity of hypoxanthine and xanthine: Several neutral and anionic Watson-Crick base pairs of xanthine were computed with MP2- and DFT-methods in order to explain the mutagenicity of hypoxanthine and xanthine. Also basepairs involving tautomeric forms of xanthine and hypoxanthine were considered. To evaluate the dimerization energies found, the dimers were classified into pairings that have the exact geometry of the canonical base pairs and those that realize a distorted Watson-Crick pairing mode. The computations show that a stable pairing which realizes the exact geometry of a canonical Watson Crick base pairing is only possible for the pairing of xanthine to cytosine, however, the base pairs are only weakly bound. The dimerization energies of both the neutral and the anionic pairing is around 0 kcal/mol, so that the xanthine-cytosine base pairs are incorporated into DNA solely because the base pairs fulfill the geometric demands of DNA polymerase, but it does not profit from any additional stabilization due to hydrogen bonding. The bonding that in the Watson-Crick pairing mode xanthine has almost no affinity to cytosine is in correspondence with the experimental result that the cytosine-xanthine base pair is incorporated into DNA at a much lower rate than the cytosine-guanine base pair, which has a very strong hydrogen bonding. While the affinity of xanthine to cytosine is very low, the computations predict that xanthine is able to form a stable Watson-Crick pairing with thymine. However, the pairing has a somewhat distorted Watson-Crick geometry, so that its high stability is outbalanced by the worsened fit to the binding pocket of DNA-polymerase. As a consequence, the xanthinethymine pairing is incorporated into DNA not at a faster, but only at a rate comparable to that of the xanthine-cytosine pairing.
In conclusion, the present thesis demonstrates that the highly desired J-type aggregation of functional perylene bisimide chromophores can be achieved by proper design of monomeric building blocks that direct self-assemble by mutual effects of hydrogen bonding and pi-pi interaction, and on the other hand, are prevented to assemble in columnar stacks owing to their twisted pi-conjugated core and sterically demanding substituents. Furthermore, the self-assembly studies gave new insights into the dynamic aggregation process of low-dimensional extended assemblies with strongly excitonically coupled chromophores. The relationship between commonly known cyanine dye aggregates like that of THIATS and that of the present PBI 1a was investigated by absorption and fluorescence spectroscopy at low temperatures down to 5 K. The formerly unprecedented functional properties of PBI aggregates that are expressed in J-type excitonic coupling hold promise for application in optoelectronic and photovoltaic devices.
Supramolecular self-assembly of perylene bisimide (PBI) dyes via non-covalent forces gives rise to a high number of different PBI architectures with unique optical and functional properties. As these properties can be drastically influenced by only slightly structural changes of the formed supramolecular ensembles (Chapter 2.1) the controlled self-assembly of PBI dyes became a central point of current research to design innovative materials with a high potential for different applications as for example in the fields of organic electronics or photovoltaics.
As PBI dyes show a strong tendency to form infinite aggregated structures (Chapter 2.2) the aim of this thesis was to precisely control their self-assembly to create small, structurally well-defined PBI assemblies in solution. Chapter 2.3 provides an overview on literature known strategies that were established to realize this aim. It could be demonstrated that especially backbone-directed intra- and intermolecular self-assembly of covalently linked Bis-PBI dyes evolved as one of the most used strategies to define the number of stacked PBI chromophores by using careful designed spacer units with regard to their length and flexibility.
By using conventional spectroscopic methods like UV/Vis and fluorescence experiments in combination with NMR measurements an in-depth comparison of the molecular and optical properties in solution both in the non-stacked and aggregated state of the target compounds could be elucidated to reveal structure-property relationships of different PBI architectures. Thus, it could be demonstrated, that spacer units that pre-organize two PBI chromophores with an inter-planar distance of r < 7 Å lead to an intramolecular folding, whereas linker moieties with a length between 7 to 11 Å result in an intermolecular self-assembly of the respective Bis-PBIs dyes via dimerization to form well-defined quadruple PBI pi-stacks. Hence, if the used spacer units ensure an inter-planar distance r > 14 Å larger oligomeric PBI pi-stacks are generated.
In Chapter 4 a detailed analysis of the exciton coupling in a highly defined H-aggregate quadruple PBI pi-stack is presented. Therefore, bay-tethered PBI dye Bis-PBI 1 was investigated by concentration-dependent UV/Vis spectroscopy in THF and toluene as well as by 2D-DOSY-NMR spectroscopy, ESI mass spectrometry and AFM measurements confirming that Bis-PBI 1 self-assembles exclusively into dimers with four closely pi-stacked PBI chromophores. Furthermore, with the aid of broadband fluorescence upconversion spectroscopy (FLUPS) ensuring broadband detection range and ultrafast time resolution at once, ultrafast Frenkel exciton relaxation and excimer formation dynamics in the PBI quadruple pi-stack within 1 ps was successfully investigated in cooperation with the group of Dongho Kim. Thus, it was possible to gain for the first time insights into the exciton dynamics within a highly defined synthetic dye aggregate beyond dimers. By analysing the vibronic line shape in the early-time transient fluorescence spectra in detail, it could be demonstrated that the Frenkel exciton is entirely delocalized along the quadruple stack after photoexcitation and immediately loses its coherence followed by the formation of the excimer state.
In Chapter 5 four well-defined Bis-PBI folda-dimers Bis-PBIs 2-4 were introduced, where linker units of different length (r < 7 Å) and steric demand were used to gain distinct PBI dye assemblies in the folded state. Structural elucidation based on in-depth UV/Vis, CD and fluorescence experiments in combination with 1D and 2D NMR studies reveals a stacking of the two PBI chromophores upon folding, where geometry-optimized structures obtained from DFT calculations suggest only slightly different arrangements of the PBI units enforced by the distinct spacer moieties. With the resulting optical signatures of Bis-PBIs 2-4 ranging from conventional Hj-type to monomer like absorption features, the first experimental proof of a PBI-based “null-aggregate” could be presented, in which long- and short-range exciton coupling fully compensate each other. Hence, the insights of this chapter pinpoint the importance of charge-transfer mediated short-range exciton coupling that can significantly influence the properties of pi-stacked PBI chromophores
In the last part of this thesis (Chapter 6), spacer-controlled self-assembly of four bay-linked Bis-PBI dyes Bis-PBIs 5-8 into well-defined supramolecular architectures was investigated, where the final aggregate structures are substantially defined by the nature of the used spacer units. By systematically extending the backbone length from 7 to 15 Å defining the inter-planar distance between the tethered chromophores, different assemblies from defined quadruple PBI pi-stacks to larger oligomeric pi-stacks could be gained upon aggregation.
In conclusion, the synthesis of nine covalently linked PBI dyes in combination with a detailed investigation of their spacer-mediated self-assembly behaviour in solution concerning structure-properties-relationships was presented within this thesis. The results confirm a strong exciton coupling in different types of Bis-PBI architectures e.g. folda-dimers or highly defined quadruple pi-stacks, which significantly influences their optical properties upon self-assembly.
In this work the catalytic activity of nanodiamond particles with different dopants and surface terminations and of diamond nanomaterials funtionalized with ruthenium-based photocatalysts was investigated, illustrating materials application in photoredox chemistry and the photo(electro)catalytic reduction of CO2. Regarding the application of diamond nanomaterials in photocatalysis, methods to fabricate and characterize several (un)doped nanoparticles with different surface termination were successfully developed. Various photocatalysts, attached to nanodiamond particles via linker systems, were tested in photoredox catalysis and the photo(electro)catalytic reduction of CO2.
Herein described is the discovery of three novel types of dimeric naphthylisoquinoline alkaloids, named mbandakamines, cyclombandakamines, and spirombandakamines. They were found in the leaves of a botanically as yet unidentified, potentially new Ancistrocladus species, collected in the rainforest of the Democratic Republic of the Congo (DRC). Mbandakamines showed an exceptional 6′,1′′-coupling, in the peri-position neighboring one of the outer axes, leading to an extremely high steric hindrance at the central axis, and to U-turn-like molecular shape, which – different from all other dimeric NIQs, whose basic structures are all quite linear – brings three of the four bicyclic ring systems in close proximity to each other. This created an unprecedented follow-up chemistry, involving ring closure reactions, leading to two further, structurally even more intriguing subclasses, the cyclo- and the spirombandakamines, displaying eight stereogenic elements (the highest total number ever found in naphthylisoquinoline alkaloids). The metabolites exhibited pronounced antiplasmodial and antitrypanosomal activities. Likewise reported in this doctoral thesis are the isolation and structural elucidation of naphthylisoquinoline alkaloids from two further potentially new Ancistrocladus species from DRC. Some of these metabolites have shown pronounced antiausterity activities against human pancreatic cancer PANC-1 cells.
The present thesis describes the development of a strategy to create discrete finite-sized supramolecular stacks of merocyanine dyes. Thus, bichromophoric stacks of two identical or different chromophores could be realized by folding of bis(merocyanine) dyes and their optical properties were discussed in terms of exciton theory. Quantum chemical calculations revealed strong exciton coupling between the chromophores within the homo- and hetero-π-stacks and the increase of the J-band of the hetero-dimers with increasing energy difference between the excited states of the chromophores could be attributed not only to the different magnitudes of transition dipole moments of the chromophores but also to the increased localization of the excitation in the respective exciton state. Furthermore, careful selection of the length of the spacer unit that defines the interplanar distance between the tethered chromophores directed the self-assembly of the respective bis(merocyanines) into dimers, trimers and tetramers comprising large, structurally precise π-stacks of four, six or eight merocyanine chromophores. It could be demonstrated that the structure of such large supramolecular architectures can be adequately elucidated by commonly accessible analysis tools, in particular NMR techniques in combination with UV/vis measurements and mass spectrometry. Supported by TDDFT calculations, the absorption spectra of the herein investigated aggregates could be explained and a relationship between the absorption properties and the number of stacking chromophores could be established based on exciton theory.
The successful synthesis of a family of donor-iridium complex-acceptor triads (T1–T6, pMV1 and mMV1) and their electrochemical and photophysical properties were presented in this work. Triarylamines (TAA) were used as donors and naphthalene diimide (NDI) as acceptor. A bis-cyclometalated phenylpyrazole iridium dipyrrin complex acts as a photosensitiser. In addition, a molecular structure of T1 was obtained by single crystal X-ray diffraction.
Transient absorption spectroscopy experiments of these triads resembled that upon excitation a photoinduced electron transfer efficiently generates long-lived, charge-separated (CS) states. Thereby, the electron-transfer mechanism depends on the excitation energy.
The presence of singlet and triplet CS states was clarified by magnetic-field dependent transient-absorption spectroscopy in the nanosecond time regime. It was demonstrated that the magnetic field effect of charge-recombination kinetics showed for the first time a transition from the coherent to the incoherent spin-flip regime.
The lifetime of the CS states could be drastically prolonged by varying the spacer between the iridium complex and the NDI unit by using a biphenyl instead of a phenylene unit in T4.
A mixed-valence (MV) state of two TAA donors linked to an iridium metal centre were generated upon photoexcitation of triad pMV1 and mMV1. The mixed-valence character in these triads was proven by the analysis of an intervalence charge-transfer (IV-CT) band in the (near-infrared) NIR spectral region by femtosecond pump-probe experiments. These findings were supported by TD-DFT calculations.
The synthesis of dyads (D1–D4) was performed. Thereby the dipyrrin ligand was substituted with electron withdrawing groups. The electrochemical and photophysical characterisation revealed that in one case (D4) it was possible to generate a CS state upon photoexcitation.
The initial goal was the conversion of Bifidobacterium adolescentis Sucrose Phosphorylase (BaSP) into a polyphenol glucosidase by structure based enzyme engineering. BaSP was chosen because of its ability to utilize sucrose, an economically viable and sustainable donor substrate, and transfer the glucosyl moiety to various acceptor substrates. The introduction of aromatic residues into the active site was considered a viable way to render it more suitable for aromatic acceptor compounds by reducing its polarity and potentially introducing π-π-interactions with the polyphenols. An investigation of the active site revealed Gln345 as a suitable mutagenesis target. As a proof of concept BaSP Q345F was employed in the glycosylation of (+)-catechin, (-)-epicatechin and resveratrol. The variant was selective for the aromatic acceptor substrates and the glucose disaccharide side reaction was only observed after almost quantitative conversion of the aromatic substrates. A crystal structure of BaSP Q345F in complex with glucose was obtained and it displayed an unexpected shift of an entire domain by 3.3 Å. A crystal structure of BaSP D192N-Q345F, an inactive variant in complex with resveratrol-3-α-D-glucosid, the glucosylation product of resveratrol, synthesized by BaSP Q345F was solved. It proved that the domain shift is in fact responsible for the ability of the variant to glycosylate aromatic compounds. Simultaneously a ligand free crystal structure of BaSP Q345F disproved an induced fit effect as the cause of the domain shift. The missing link, a crystal structure of BaSP Q345F in the F-conformation is obtained. This does not feature the domain shift, but is in outstanding agreement with the wildtype structure. The domain shift is therefore not static but rather a step in a dynamic process. It is further conceivable that the domain shifted conformation of BaSP Q345F resembles the open conformation of the wild type and that an adjustment of a conformational equilibrium as a result of the Q345F point mutation is observed. An investigation into the background reaction, the formation of glucose-glucose disaccharides of BaSP Q345F and three further variants that addressed the same region (L341C, D316C-L341C and D316C-N340C) revealed the formation of nigerose by BaSP Q345F.
In this work the influence of “active” bridge units on the electron transfer (ET) mechanism within organic donor-bridge-electrode arrays in self-assembled monolayers (SAMs) was studied by spectroscopic and electrochemical methods. In the first part of this work ferrocenealkanethiols 1 – 3 and the ferrocenearylthiols 4, 5 were investigated to get experience in the monolayer preparation for measuring ET rates. Cyclic voltammetry of the monolayers indicates that homogeneously mixed monolayers containing redox active molecules and dummy molecules were formed. For the known ferrocenealkanethiols 1 – 3 the ET rates could be confirmed compared to the ones measured by Creager et al. [206]. As expected the ET rate decreases by increasing chain length of the alkane spacer from 2 to 3. Changing the bonding between the redox centre and the alkane spacer with the same bridge lenght, e. g. by using a carboxy-group in case of 1, does not influence the ET behaviour very strong. The aromatic ferrocenethiols 4 and 5 show very high ET rates due to the strong conjugated system although the distance between the redox centre and the electrode is comparable to the C8-alkyl compound 2. The electronic coupling factors all indicate a nonadiabatic ET between the redox centre and the electrode. As expected the electronic coupling factors increase with decreasing spacer length or with an enlarged conjugated system. To sum up, experience in monolayer preparation could be obtained, the measured ET rates for well known ferrocenealkane-compounds 1 - 3 could be verified and the information could be transferred to the conjugated systems 4 and 5. In the second part the triarylamine- 29, 32 and the phenothiazinealkanethiol 35 have been examined relative to their ET behaviour in mixed monolayers. The cyclic voltammograms of the diluted monolayers indicate that homogeneously formed monolayers are present. The ET rates of triarylamine- 29, 32 and phenothiazinealkanethiols 35 are 10 to 100 times higher than compared to ferrocenealkanethiols with equal chain length[183, 206], whereas in a [Ru(bpy)2(pp)]+-containing monolayer the same value was observed [177]. Almost two parameters influence the ET rate constant: the electronic coupling matrix element and the reorganisation energy  [209]. The ET rate in donor substituted alkanethiols is mainly influenced by the reorganisation energy  [177] and even small changes have a dramatic effect on the observed processes, therefore an increasing ET rate from the ferrocene (high reorganisation energy) over the phenothiazine 35 and the [Ru(bpy)2(pp)]+ to the triarylamine chromophores 29 and 32 (low reorganisation energy) is observed. Furthermore the bonding between the redox centres and the alkane spacer plays an important role on the ET rate in case of the triarylamines 29 and 32 opposite to the assumption made by Creager et al. that the connection does not play any role. For the electron rich ether connected compound 29 the ET is not only dominated by the reorganisation energy but also by mesomeric effects where the positive charge of the electron rich derivative 29 is more located at the ether function so that the chain is formally shortend by one atom resulting in higher ET rates than compared to 32. In the third part of the thesis a series of “molecular wires” consisting of methoxy- or chloro-substituted triarylamines and phenothiazines with different bridge units and bridge length between the redox centre and the anchor thiol function have been prepared in order to investigate their ET-behaviour. Cyclic voltammetry and UV/vis-spectroscopy show that the oxidation potential and the energetic states could be controlled very well by introducing different redox centres and bridge units resulting in a decreasing oxidation potential of the redox centres and a bathochromic shift of the absorption bands in the UV/vis-spectra. Also the densitiy of the chromophores in mixed monolayers could be controlled very well for only three compounds (49, 52 and 87) with nitrile-substituted bridges reliable ET rates could be obtained. In these chromophores the ET rate decreases by increasing the density of the redox active molecules in the mixed monolayers indicating that the adsorption geometry changes with coverage with the chromophores tilting to a more upright orientation as the surface becomes more crowded. For all other compounds the measurements were limited by the fast ET rates. Conformational, as well as a very weak distance dependence of the ET resulting in very high ET rates [172] or unfavourable HOMO-LUMO energies of the donor, bridge and the electrode are reasons for this behaviour. The fact that compound 49 shows almost the same rate constant independent of the length (n = 2 or n = 3) may indicate that a hopping process is operating for which a much weaker length dependence is expected than in the case of a superexchange.
The catalytic splitting of water into its elements is an important reaction to establish hydrogen as a solar fuel. The bottle-neck of this process is considered to be the oxidative half reaction generating oxygen, and good catalysts are required to handle the complicated redox chemistry involved. As can be learned from nature, the incorporation of the catalytically active species into an appropriate matrix can help to improve the overall performance. Thus, the aim of the present thesis was to establish novel supramolecular approaches to improve water oxidation catalysis using the catalytically active {Ru(bda)} fragment as key motive (bda = 2,2'-bipyridine-6,6'-dicarboxylate).
First, the synthesis of ruthenium catalysts gathering three {Ru(bda)} water oxidation subunits in a macrocyclic fashion is described. By using bridging bipyridine ligands of different lengths, metallosupramolecular macrocycles with distinct sizes have been obtained. Interestingly, an intermediate ring size has been proven to be optimal for the catalytic water oxidation. Detailed kinetic, spectroscopic, and theoretical studies helped to identify the reaction mechanism and to rationalize the different catalytic activities. Furthermore, solubilizing side chains have been introduced for the most active derivative to achieve full water solubility.
Secondly, the {Ru(bda)} fragment was embedded into supramolecular aggregates to generate more stable catalytic systems compared to a homogeneous reference complex. Therefore, the catalyst fragment was equipped with axial perylene bisimide (PBI) ligands, which facilitate self-assembly. Moreover, the influence of the different accessible aggregate morphologies on the catalytic performance has been investigated.
Perylene bisimide (PBI) dyes are a widely used class of industrial pigments, and currently have gained significant importance for organic-based electronic and optical devices. Structural modification at the PBI core results in changes of the optical and electronic properties, which enable tailored functions. Moreover, the aggregation behavior of PBIs is alterable and controllable to achieve new materials, among which organogels are of particular interest because of their potential for applications as supramolecular soft materials. In this work, new PBI-based organic gelators were designed, synthesized, and characterized, and the aggregation behaviors under different conditions were intensively studied by various spectroscopic and microscopic methods. In chapter 2, a brief overview is given on the structural and functional features of organogel systems. The definition, formation and reversibility of organogels are introduced. Some examples on dye based organogel are selected, among which PBI-based organogelators reported so far are especially emphasized. Some basic knowledges of supramolecular chirality are also overviewed such as characterization, amplification, and symmetry breaking of the chiral aggregates. According to our former experiences, PBIs tend to form aggregates because the planer aromatic cores interact with one another by pi-pi interaction. In chapter 3, a new PBI molecule is introduced which possesses amide groups between the conjugated core and periphery alkyl chains. It is found that well oriented aggregates are formed by hydrogen bonding and the pi-pi interaction of the cores. These interactions enable the aggregates to grow in one-dimension forming very long fibers, and these fibers further intercross to 3D network structures, e.g., organogels. In comparison to the very few PBI-based gelators reported before, one advantage of this gelator is that, it is more versatile and can gelate a wide range of organic solvents. Moreover, the well-organized fibers that are composed of extended π-stacks provide efficient pathways for n-type charge carriers. Interestingly, AFM studies reveal that the PBI molecules form well-defined helical fibers in toluene. Both left-handed (M) and right-handed (P) helicities can be observed without any preference for one handedness because the building block is intrinsically achiral. In chapter 4, we tried to influence the M/P enantiomeric ratio by applying external forces. For example, we utilized chiral solvents to generate chiral aggregates with a preferential handedness. AFM analysis of the helices showed that a enantiomeric ratio of about 60: 40 can be achieved by aggregation in chiral solvents R- or S-limonene. Moreover, the long aggregated fibres can align at macroscopic level in vortex flows upon rotary stirring In chapter 5, bulky tetra-phenoxy groups are introduced in the bay area of the PBI gelator. The conjugated core of the new molecule is now distorted because of the steric hindrance. UV/Vis studies reveal a J-type aggregation in apolar solvents like MCH due to intermolecular pi-pi-stacking and hydrogen-bonding interactions. Microscopic studies reveal formation of columnar aggregates in apolar solvent MCH, thus this molecule lacks the ability to form gels in this solvent, but form highly fluorescent lyotropic mesophases at higher concentration. On the other hand, in polar solvents like acetone and dioxane, participation of the solvent molecules in hydrogen bonding significantly reduced the aggregation propensity but enforced the gel formation. The outstanding fluorescence properties of the dye in both J-aggregated viscous lyotropic mesophases and bulk gel phases suggest very promising applications in photonics, photovoltaics, security printing, or as fluorescent sensors. In chapter 6, we did some studies on combining PBI molecules with inorganic gold nanorods. Gold nanorods were synthesized photochemically. By virtue of the thioacetate functionalized PBIs, the rods were connected end to end to form gold nanochains, which were characterized by absorption spectra and TEM measurement. Such chromophore-nanorod hybrids might be applied to guide electromagnetic radiation based on optical antenna technology.
RNA molecules play diverse roles in biological systems. Post-transcriptional RNA modifications and dynamic structures enhance the functional diversity of RNA. A prerequisite for studying their biological significance is the availability of reliable methods for the detection of RNA modifications and structures. Several promising approaches have been developed in the last few decades; however, efficient, and versatile tools are still required to study the dynamic features of RNA. This thesis focuses on the development of nucleic acid catalysts as a tool to address the current needs in studying RNA. The major part of this thesis aimed at the development of deoxyribozymes as a tool for the detection of RNA modifications. Using in vitro selection from a random DNA library, we found deoxyribozymes that are sensitive to N 6 -isopentenyladenosine (i6A), a native tRNA modification and structural analogue of m6A. The in vitro evolution identified three classes of DNA enzymes: AA, AB08, and AC17 DNAzymes that showed distinct response to i6A modification and showed strong discrimination between structural analogues, i.e., m6A and i6A. In the continuation of the project, we attempted to develop RNA-cleaving deoxyribozymes that differentially respond to monomethylated cytidine isomers, 3-methylcytidine (m3C), N4 - methylcytidine (m4C), and 5-methylcytidine (m5C). Several deoxyribozymes were identified from in vitro selection, which are selective for a specific methylated cytidine isomer. The characterization of AL112, AM101, AN05, and AK104 catalysts confirmed the successful evolution of modification-specific and general deoxyribozymes that showed a broad substrate scope. In order to accelerate the DNAzymes discovery, a high throughput sequencing method (DZ-seq) was established that directly quantifies the RNA cleavage activity and cleavage site from deep sequencing data. The libraries contained information about cleavage status, cleavage site and sequence of deoxyribozymes and RNA substrate. The fraction cleaved (FC) data obtained from Dz-seq was validated for a subset of deoxyribozmes using conventional gel based kinetic assay and showed a good linear correlation (R2 = 0.91). Dz-seq possesses a great potential for the discovery of novel deoxyribozymes for the analysis of various RNA modifications in the future. The second objective of the current study was the development of structure-specific RNA labeling ribozymes. Here, we attempted to develop ribozymes that targets RNA of interest by structure-specific interaction rather than base-pairing and focused on a specific RNA G-quadruplex as the target. Two subsequent selection experiments led to the identification of the adenylyltransferase ribozymes AO10.2 and AR9. The partial characterization of these catalysts showed that A010.2 was unable to recognize intact BCL2 structure, but it turned out as the first reported trans-active ribozyme that efficiently labeled uridine in a defined substrate RNA hybridized to the ribozyme. The other ribozyme AR9 was shown to serve as a trans-active, self-labeling ribozyme that catalyzed adenylyl transferase reaction in the presence of the intact BCL2 sequence. Based on these preliminary findings, we envision that AR9 could potentially serve as a reporter RNA by self-labeling in the presence of an RNA G-quadruplex. However, both AO10.2 and AR9 still require more detailed characterization for their potential applications.
The aim of the thesis was to develop water soluble poly(2-oxazoline) (POx) copolymers with new side group functionalities, which can be used for the formation of hydrogels in biomedical applications and for the development of peptide-polymer conjugates.
First, random copolymers of the monomer MeOx or EtOx with ButEnOx and EtOx with DecEnOx were synthesized and characterized. The vinyl functionality brought into the copolymer by the monomers ButEnOx and DecEnOx would later serve for post-polymerization functionalization. The synthesized copolymers were further functionalized with thiols via post-polymerization functionalization using a newly developed synthesis protocol or with a protected catechol molecule for hydrogel formation. For the formation of peptide-polymer conjugates, a cyclic thioester, namely thiolactone acrylamide and an azlactone precursor, whose synthesis was newly developed, were attached to the side chain of P(EtOx-co-ButEnOx) copolymers.
The application of the functionalized thiol copolymers as hydrogels using thiol-ene chemistry for cross-linking was demonstrated. The swelling behavior and mechanical properties were characterized. The hydrophilicity of the network as well as the cross-linking density strongly influenced the swelling behavior and the mechanical strength of the hydrogels. All hydrogels showed good cell viability results.
The hydrogel networks based on MeOx and EtOx were loaded with two dyes, fluorescein and methylene blue. It was observed that the uptake of the more hydrophilic dye fluorescein depended more on the ability of the hydrogel to swell. In contrast, the uptake of the more hydrophobic dye methylene blue was less dependent on the swelling degree, but much more on the hydrophilicity of the network.
For the potential application as cartilage glue, (biohybrid) hydrogels were synthesized based on the catechol-functionalized copolymers, with and without additional fibrinogen, using sodium periodate as the oxidizing agent. The system allowed for degradation due to the incorporated ester linkages at the cross-linking points. The swelling behavior as well as the mechanical properties were characterized. As expected, hydrogels with higher degrees of cross-linking showed less swelling and higher elastic modulus. The addition of fibrinogen however increased the elasticity of the network, which can be favorable for the intended application as a cartilage glue. Biological evaluation clearly demonstrated the advantage of degradable ester links in the hydrogel network, where chondrocytes were able to bridge the artificial gap in contrast to hydrogels without any ester motifs.
Lastly, different ways to form peptide-polymer conjugates were presented. Peptides were attached with the thiol of the terminal cysteine group to the vinyl side chain of P(EtOx-co-ButEnOx) copolymers by radical thiol-ene chemistry. Another approach was to use a cyclic thioester, thiolactone, or an azlactone functionality to bind a model peptide via native chemical ligation. The two latter named strategies to bind peptides to POx side chains are especially interesting as one and in the case of thiolactone two free thiols are still present at the binding site after the reaction, which can, for example, be used for further thiol-ene cross-linking to form POx hydrogels.
In summary, side functional poly(oxazoline) copolymers show great potential for numerous biomedical applications. The various side chain functionalities can be introduced by an appropriate monomer or by post-polymerization functionalization, as demonstrated. By their multi-functionality, hydrogel characteristics, such as cross-linking degree and mechanical strength, can be fine-tuned and adjusted depending on the application in the human body. In addition, the presented chemoselective and orthogonal reaction strategies can be used in the future to synthesize polymer conjugates, which can, for example, be used in drug delivery or in tissue regeneration.
The present thesis demonstrates the importance of the solid state packing of dipolar merocyanine dyes with regard to charge transport and exciton coupling.
Due to the charge transport theory for disordered materials, it is expected that high ground state dipole moments in amorphous thin films lead to low mobility values due to a broadening of the density of states. However, due to their inherent dipolarity, merocyanine dyes usually align in antiparallel dimers in an ordered fashion. The examination of twenty different molecules with ground state dipole moments up to 15.0 D shows that by a high dipolarity and well-defined sterics, the molecules pack in a highly regular two-dimensional brickwork-type structure, which is beneficial for hole transport. Utilization of these molecules for organic thin-film transistors (OTFTs) leads to hole mobility values up to 0.21 cm²/Vs. By fabrication of single crystal field-effect transistors (SCFETs) for the derivative showing the highest mobility values in OTFTs, even hole mobilities up to 2.34 cm²/Vs are achieved. Hence, merocyanine based transistors show hole mobility values comparable to those of conventional p-type organic semiconductors and therefore high ground state dipole moments are not necessarily disadvantageous regarding high mobility applications.
By examination of a different series of ten merocyanine dyes with the same chromophore backbone but different donor substituents, it is demonstrated that the size of the donor has a significant influence on the optical properties of thin films. For small and rigid donor substituents, a hypsochromic shift of the absorption compared to the monomer absorption in solution is observed due to the card stack like packing of the molecules in the solid state. By utilization of sterical demanding or flexible donor substituents, a zig-zag type packing is observed, leading to a bathochromical shift of the absorption. These packing motifs and spectral shifts with an offset of 0.93 eV of the H- and J-bands comply with the archetype examples of H- and J-aggregates from Kasha’s exciton theory.
The present thesis demonstrates the potential of dipolar aggregation of merocyanine dyes as novel directional and specific supramolecular binding motif for the creation of more elaborate supramolecular architectures beyond simple dimers. Furthermore, the self-assembly studies into bis(merocyanine) nanorods gave new insights into the kinetics of morphogenesis in supramolecular aggregates.
The present thesis introduce different synthetic strategies towards a variety of polycyclic aromatic dicarboximides (PADIs) with highly interesting and diverse properties. This included tetrachlorinated, tetraaryloxy- and tetraaryl-substituted dicarboximides, fused acceptor‒donor(‒acceptor) structures as well as sterically shielded rylene and nanographene dicarboximides. The properties and thus the disclosure of structure‒property relationships of the resulting dyes were investigated in detail among others with UV‒vis absorption spectroscopy, fluorescence spectroscopy, cyclic voltammetry and single crystal X-ray analysis. For instance, some of the fused and substituted PADIs offer strong absorption of visible and near infrared (NIR) light, NIR emission and low-lying LUMO levels. On the contrary, intriguing optical features in the solid-state characterize the rylene dicarboximides with their bulky N-substituents, while the devised sterically enwrapped nanographene host offered remarkable complexation capabilities in solution.
The chirality of the interlocked bay-arylated perylene motif is investigated upon its material prospect and the enhancement of its chiroptical response to the NIR spectral region. A considerable molecular library of inherently chiral perylene bisimides (PBIs) was utilized as acceptors in organic solar cells to provide decent device performances and insights into the structure-property relationship of PBI materials within a polymer blend. For the first time in the family of core-twisted PBIs, the effects of enantiopurity on the device performance was thoroughly investigated. The extraordinary structural sensitivity of CD spectroscopy served as crucial analytical tool to bridge the highly challenging gap between molecular properties and device analytics by proving the excitonic chirality of a helical PBI dimer. The chirality of this perylene motif could be further enhanced on a molecular level by both the expansion and the enhanced twisting of the π-scaffold to achieve a desirable strong chiroptical NIR response introducing a new family of twisted QBI-based nanoribbons. These achievements could be substantially further developed by expanding this molecular concept to a supramolecular level. The geometrically demanding supramolecular arrangement necessary for the efficient excitonic coupling was carefully encoded into the molecular design. Accordingly, the QBIs could form the first J-type aggregate constituting a fourfold-stranded superhelix of a rylene bisimide with strong excitonic chirality. Therefore, this thesis has highlighted the mutual corroboration of experimental and theoretical data from the molecular to the supramolecular level. It has demonstrated that for rylene bisimide dyes, the excitonic contribution to the overall chiroptical response can be designed and rationalized. This can help to pave the way for new organic functional materials to be used for
chiral sensing or chiral organic light-emitting devices.