@phdthesis{Bass2011, author = {Baß, Utz}, title = {Analysis of MBE-grown II-VI Hetero-Interfaces and Quantum-Dots by Raman Spectroscopy}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-73413}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2011}, abstract = {The material system of interest in this thesis are II-VI-semiconductors. The first part of this thesis focuses on the formation of self-assembled CdSe-based quantum dots (QD) on ZnSe. The lattice constants of ZnSe and CdSe differ as much as about 7\\% and therefore a CdSe layer grown on top of ZnSe experiences a huge strain. The aspired strain relief constitutes in the self-assembly of QDs (i.e. a roughened layer structure). Additionally, this QD layer is intermixed with Zn as this is also a possibility to decrease the strain in the layer. For CdSe on ZnSe, in Molecular Beam Epitaxy (MBE), various QD growth procedures were analysed with respect to the resulting Cd-content of the non-stoichiometric ternary (Zn,Cd)Se. The evaluation was performed by Raman Spectroscopy as the phonon frequency depends on the Cd-content. The second part of the thesis emphasis on the interface properties of n-ZnSe on n-GaAs. Different growth start procedures of the ZnSe epilayer may lead to different interface configurations with characteristic band-offsets and carrier depletion layer widths. The analysis is mainly focused on the individual depletion layer widths in the GaAs and ZnSe. This non-destructive analysis is performed by evaluating the Raman signal which comprises of phonon scattering from the depleted regions and coupled plasmon-phonon scattering from regions with free carriers.}, subject = {Zwei-Sechs-Halbleiter}, language = {en} } @phdthesis{Chen2006, author = {Chen, Zhijian}, title = {pi-Stacks Based on Self-Assembled Perylene Bisimides : Structural, Optical, and Electronic Properties}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-19940}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2006}, abstract = {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.}, subject = {Perylenderivate}, language = {en} } @article{DostalFennelKochetal.2018, author = {Dost{\´a}l, Jakub and Fennel, Franziska and Koch, Federico and Herbst, Stefanie and W{\"u}rthner, Frank and Brixner, Tobias}, title = {Direct observation of exciton-exciton interactions}, series = {Nature Communications}, volume = {9}, journal = {Nature Communications}, doi = {10.1038/s41467-018-04884-4}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-226271}, year = {2018}, abstract = {Natural light harvesting as well as optoelectronic and photovoltaic devices depend on efficient transport of energy following photoexcitation. Using common spectroscopic methods, however, it is challenging to discriminate one-exciton dynamics from multi-exciton interactions that arise when more than one excitation is present in the system. Here we introduce a coherent two-dimensional spectroscopic method that provides a signal only in case that the presence of one exciton influences the behavior of another one. Exemplarily, we monitor exciton diffusion by annihilation in a perylene bisimide-based J-aggregate. We determine quantitatively the exciton diffusion constant from exciton-exciton-interaction 2D spectra and reconstruct the annihilation-free dynamics for large pump powers. The latter enables for ultrafast spectroscopy at much higher intensities than conventionally possible and thus improves signal-to-noise ratios for multichromophore systems; the former recovers spatio-temporal dynamics for a broad range of phenomena in which exciton interactions are present.}, language = {en} } @phdthesis{Fetsch2014, author = {Fetsch, Corinna}, title = {Polypeptoide - Synthese und Charakterisierung}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-109157}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2014}, abstract = {Die vorliegende Arbeit befasste sich mit der bisher relativ unbekannten Polymerklasse der Polypeptoide, die hinsichtlich ihrer Verwendung als Biomaterial n{\"a}her untersucht werden sollte. Hierbei war die Untersuchung des Polymerisationssystems ein wesentlicher Schwerpunkt. Dies beinhaltete zum einen die Synthesen verschiedener Monomere sowie deren Polymerisationskinetiken und zum anderen Studien {\"u}ber die Stabilit{\"a}t des aktiven Kettenendes. Um mehr {\"u}ber die Polypeptoide zu erfahren, wurden die erhaltenen Homopolymere nach der Strukturanalyse hinsichtlich ihrer physikochemischen Eigen-schaften untersucht. Im Anschluss erfolgte die Synthese von (amphiphilen) Blockco-polypeptoiden, die sich in w{\"a}ssrigen L{\"o}sungen zu definierten Morphologien zusammen-lagern. Die resultierenden Morphologien, sowohl mizellare als auch vesikul{\"a}re Strukturen, wurden mit verschiedenen Methoden, wie z. B. der Pyren-Fluoreszenz-Spektroskpie und der dynamischen Lichtstreuung, untersucht. Erste Erkenntnisse {\"u}ber die Biokompatibilit{\"a}t der Polypeptoide sollte die Bestimmung der Zellviabilit{\"a}t in verschiedenen Polymerl{\"o}sungen liefern. Die verschiedenen Studien {\"u}ber die Polypeptoide zeigten, dass diese Polymerklasse {\"u}ber eine besonders lebende Polymerisation synthetisiert werden kann. Dabei resultieren Produkte, die sich durch eine Poisson-Verteilung und eine hohe Endgruppengenauigkeit auszeichnen. Zus{\"a}tzlich bestehen Polypeptoide aus einem abbaubaren R{\"u}ckgrat und, im Vergleich zu den Polypeptiden, besitzen sie eine erh{\"o}hte proteolytische Stabilit{\"a}t. Amphiphile Blockcopolypeptoide sind zudem in der Lage, sich in L{\"o}sung zu verschiedenen Morphologien anzuordnen. Durch die Variierung der Seitenkette und des f kann sowohl die Selbstorganisation als auch das Mikroumfeld der Aggregate abgestimmt werden. Dar{\"u}ber hinaus k{\"o}nnen die amphiphile Blockcopolymere, die sich zu Mizellen anordnen, hydrophobe Substanzen solubilisieren. Polypeptoide liefern all die n{\"o}tige chemische Vielseitigkeit und potentielle Biokompatibilit{\"a}t, um bestehende sowie neuartige Probleme in biomedizinischen Anwendungen zu bew{\"a}ltigen. Zuk{\"u}nftige in vivo und in vitro Test werden das Potential, aber auch die Grenzen dieser neuen Polymerklasse als Biomaterial zeigen.}, subject = {Polymerisation}, language = {de} } @article{FetschGaitzschMessageretal.2016, author = {Fetsch, Corinna and Gaitzsch, Jens and Messager, Lea and Battaglia, Giuseppe and Luxenhofer, Roberts}, title = {Self-Assembly of Amphiphilic Block Copolypeptoids - Micelles, Worms and Polymersomes}, series = {Scientific Reports}, volume = {6}, journal = {Scientific Reports}, doi = {10.1038/srep33491}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-147855}, pages = {33491}, year = {2016}, abstract = {Polypeptoids are an old but recently rediscovered polymer class with interesting synthetic, physico-chemical and biological characteristics. Here, we introduce new aromatic monomers, N-benzyl glycine N-carboxyanhydride and N-phenethyl glycine N-carboxyanhydride and their block copolymers with the hydrophilic polysarcosine. We compare their self-assembly in water and aqueous buffer with the self-assembly of amphiphilic block copolypeptoids with aliphatic side chains. The aggregates in water were investigated by dynamic light scattering and electron microscopy. We found a variety of morphologies, which were influenced by the polymer structure as well as by the preparation method. Overall, we found polymersomes, worm-like micelles and oligo-lamellar morphologies as well as some less defined aggregates of interconnected worms and vesicles. Such, this contribution may serve as a starting point for a more detailed investigation of the self-assembly behavior of the rich class of polypeptoids and for a better understanding between the differences in the aggregation behavior of non-uniform polypeptoids and uniform peptoids.}, language = {en} } @article{GrandeSoberatsHerbstetal.2018, author = {Grande, Vincenzo and Soberats, Bartolome and Herbst, Stefanie and Stepanenko, Vladimir and W{\"u}rthner, Frank}, title = {Hydrogen-bonded perylene bisimide J-aggregate aqua material}, volume = {9}, issn = {2041-6539}, doi = {10.1039/C8SC02409J}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-204715}, pages = {6904-6911}, year = {2018}, abstract = {A new twelvefold methoxy-triethyleneglycol-jacketed tetraphenoxy-perylene bisimide (MEG-PBI) amphiphile was synthesized that self-assembles into two types of supramolecular aggregates in water: red-coloured aggregates of low order and with weak exciton coupling among the PBIs and blue-coloured strongly coupled J-aggregates consisting of a highly ordered hydrogen-bonded triple helix of PBIs. At room temperature this PBI is miscible with water at any proportions which enables the development of robust dye aggregates in solution, in hydrogel states and in lyotropic liquid crystalline states. In the presence of 60-95 wt\% water, self-standing coloured hydrogels exhibit colour changes from red to blue accompanied by a fluorescence light-up in the far-red region upon heating in the range of 30-50 °C. This phenomenon is triggered by an entropically driven temperature-induced hydrogen-bond-directed slipped stacking arrangement of the MEG-PBI chromophores within structurally well-defined J-aggregates. This versatile aqua material is the first example of a stable PBI J-aggregate in water. We anticipate that this study will open a new avenue for the development of biocompatible functional materials based on self-assembled dyes and inspire the construction of other hydrogen-bonded supramolecular materials in the highly competitive solvent water.}, language = {en} } @article{HahnLuxenhoferHeltenetal.2021, author = {Hahn, Lukas and Luxenhofer, Robert and Helten, Holger and Forster, Stefan and Fritze, Lars and Polzin, Lando and Keßler, Larissa}, title = {ABA Type Amphiphiles with Poly(2-benzhydryl-2-oxazine) Moieties: Synthesis, Characterization and Inverse Thermogelation}, series = {Macromolecular Chemistry and Physics}, volume = {222}, journal = {Macromolecular Chemistry and Physics}, number = {17}, doi = {10.1002/macp.202100114}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-265124}, year = {2021}, abstract = {Thermoresponsive polymers are frequently involved in the development of materials for various applications. Here, polymers containing poly(2- benzhydryl-2-oxazine) (pBhOzi) repeating units are described for the first time. The homopolymer pBhOzi and an ABA type amphiphile comprising two flanking hydrophilic A blocks of poly(2-methyl-2-oxazoline) (pMeOx) and the hydrophobic aromatic pBhOzi central B block (pMeOx-b-pBhOzi-b-pMeOx) are synthesized and the latter is shown to exhibit inverse thermogelling properties at concentrations of 20 wt.\% in water. This behavior stands in contrast to a homologue ABA amphiphile consisting of a central poly(2-benzhydryl-2-oxazoline) block (pMeOx-b-pBhOx-b-pMeOx). No inverse thermogelling is observed with this polymer even at 25 wt.\%. For 25 wt.\% pMeOx-b-pBhOzi-b-pMeOx, a surprisingly high storage modulus of ≈22 kPa and high values for the yield and flow points of 480 Pa and 1.3 kPa are obtained. Exceeding the yield point, pronounced shear thinning is observed. Interestingly, only little difference between self-assemblies of pMeOx-b-pBhOzi-b-pMeOx and pMeOx-b-pBhOx-b-pMeOx is observed by dynamic light scattering while transmission electron microscopy images suggest that the micelles of pMeOx-b-pBhOzi-b-pMeOx interact through their hydrophilic coronas, which is probably decisive for the gel formation. Overall, this study introduces new building blocks for poly(2-oxazoline) and poly(2-oxazine)-based self-assemblies, but additional studies will be needed to unravel the exact mechanism.}, language = {en} } @article{HechtLeowanawatGerlachetal.2020, author = {Hecht, Markus and Leowanawat, Pawaret and Gerlach, Tabea and Stepanenko, Vladimir and Stolte, Matthias and Lehmann, Matthias and W{\"u}rthner, Frank}, title = {Self-Sorting Supramolecular Polymerization: Helical and Lamellar Aggregates of Tetra-Bay-Acyloxy Perylene Bisimide}, series = {Angewandte Chemie International Edition}, volume = {59}, journal = {Angewandte Chemie International Edition}, number = {39}, doi = {10.1002/anie.202006744}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-224586}, pages = {17084 -- 17090}, year = {2020}, abstract = {A new perylene bisimide (PBI), with a fluorescence quantum yield up to unity, self-assembles into two polymorphic supramolecular polymers. This PBI bears four solubilizing acyloxy substituents at the bay positions and is unsubstituted at the imide position, thereby allowing hydrogen-bond-directed self-assembly in nonpolar solvents. The formation of the polymorphs is controlled by the cooling rate of hot monomer solutions. They show distinctive absorption profiles and morphologies and can be isolated in different polymorphic liquid-crystalline states. The interchromophoric arrangement causing the spectral features was elucidated, revealing the formation of columnar and lamellar phases, which are formed by either homo- or heterochiral self-assembly, respectively, of the atropoenantiomeric PBIs. Kinetic studies reveal a narcissistic self-sorting process upon fast cooling, and that the transformation into the heterochiral (racemic) sheetlike self-assemblies proceeds by dissociation via the monomeric state.}, language = {en} } @phdthesis{Huber2007, author = {Huber, Valerie}, title = {Selbstorganisation von semisynthetischen Zinkchlorinen zu biomimetischen Lichtsammelsystemen und definierten Nanostrukturen}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-24517}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2007}, abstract = {Diese Arbeit besch{\"a}ftigt sich mit der Selbstorganisation von Zinkchlorin-Farbstoffen, welche sich strukturell von Chlorophyllen ableiten. Im Gegensatz zu allen anderen bakteriellen und pflanzlichen Lichtsammelpigmenten ist es den Bakteriochlorophyllen c, d und e der Lichtsammelsysteme gr{\"u}ner phototropher Bakterien m{\"o}glich, allein durch nichtkovalente Wechselwirkungen zwischen den Farbstoff-Molek{\"u}len, ohne die Beteiligung von Proteinen, r{\"o}hrenf{\"o}rmige Antennensysteme auszubilden, welche die am dichtest gepackten und effizientesten Lichtsammelsysteme in der Natur darstellen. Um einen Betrag zur Aufkl{\"a}rung dieser biologisch wichtigen Aggregate zu leisten, wurden im ersten Teil dieser Arbeit Zinkchlorine als Modellverbindungen f{\"u}r BChl c hergestellt. Mit den neu synthetisierten Zinkchlorinen ist es gelungen, Modellsysteme der nat{\"u}rlichen BChl-Selbstorganisate herzustellen, welche sich im Gegensatz zu den bisher in der Literatur beschriebenen Zinkchlorin-Aggregaten durch eine gute und dauerhafte L{\"o}slichkeit auszeichnen. Diese Eigenschaft erlaubte es sowohl spektroskopische als auch mikroskopische Untersuchungen zur Aufkl{\"a}rung der Aggregatstruktur durchzuf{\"u}hren. Durch Rasterkraftmikroskopie an den Zinkchlorin Aggregaten konnte erstmals ein mikroskopischer Beweis der stabf{\"o}rmigen Struktur von Aggregaten dieser Substanzklasse erhalten werden. Der zweite Teil dieser Arbeit besch{\"a}ftigt sich mit Zinkchlorinen, denen aufgrund einer methylierten 31-Hydroxy-Gruppe die F{\"a}higkeit zur R{\"o}hrenbildung fehlt, die aber durch Koordinationsbindungen und p-p-Wechselwirkungen weiterhin Stapel bilden k{\"o}nnen. Temperaturabh{\"a}ngige UV/Vis- und CD-spektroskopische Studien offenbarten die reversible Bildung von l{\"o}slichen, chiralen Zinkchlorin-Stapelaggregaten. Rasterkraft- und rastertunnelmikroskopische Untersuchungen zeigen die Bildung von zwei Typen p-gestapelter Aggregate auf hoch geordnetem Graphit.}, subject = {Farbstoff}, language = {de} } @phdthesis{Li2009, author = {Li, Xueqing}, title = {Hydrogen Bond-directed Self-assembly of Perylene Bisimide Organogelators}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-43727}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2009}, abstract = {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 \&\#960;-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.}, subject = {Perylenderivate}, language = {en} }