Refine
Has Fulltext
- yes (20)
Is part of the Bibliography
- yes (20)
Year of publication
- 2018 (20) (remove)
Document Type
- Doctoral Thesis (10)
- Journal article (8)
- Preprint (2)
Keywords
- self-assembly (3)
- Squaraine (2)
- energy transfer (2)
- fluorescence (2)
- liquid crystals (2)
- Bodipy (1)
- C-C coupling (1)
- Chemische Reaktion (1)
- Chemische Synthese (1)
- Chromophor (1)
- Click-Chemie (1)
- DNA catalyst (1)
- Dicarboximide (1)
- Dicarboximides (1)
- Dyad (1)
- Dyade (1)
- Elektronentransfer (1)
- Energieaufnahme (1)
- Energy Transfer (1)
- Excitons (1)
- Exziton (1)
- Flüssigkristall (1)
- Fulleren-Netzwerk (1)
- Fullerene (1)
- Hekate (1)
- Helicität <Chemie> (1)
- Helix- and Zick-Zack-Konformere (1)
- Helix- and Zig-Zag-Conformers (1)
- Hexaarylbenzene (1)
- Isolierung <Chemie> (1)
- J- and H-Aggregate (1)
- J- and H-Aggregates (1)
- Katalyse (1)
- Kupplungsreaktion (1)
- Käfigverbindungen (1)
- Lipidmembran (1)
- Magnetfeldeffekt (1)
- Mesogen (1)
- Metallosupramolekulare Chemie (1)
- N6-methyladenosine (1)
- Nanosegregation (1)
- Naphthylisochinolinalkaloide (1)
- Natural products (1)
- Naturstoffe (1)
- Nematische Phase (1)
- Oligomere (1)
- Oligomers and Polymers (1)
- Organische Synthese (1)
- Polycyclic aromatic hydrocarbons (1)
- Polycyclische Aromaten (1)
- Porphyrin (1)
- Pyrenderivate (1)
- Pyrene (1)
- RNA (1)
- RNA Aptamer (1)
- RNA modification (1)
- Raumfüllung (1)
- Ruthenium Komplexe (1)
- Selbstorganisation (1)
- Sonogashira (1)
- Sonogashira-Hagihara-Reaktion (1)
- Space filling (1)
- Sphingolipid (1)
- Sphingolipide (1)
- Squarain Farbstoffe (1)
- Squaraine Dyes (1)
- Strukturaufklärung (1)
- Supramolecular Chemistry (1)
- Supramolekulare Chemie (1)
- Synthese (1)
- Thermotroper Flüssigkristall (1)
- Totalsynthese (1)
- Tribenzotriquinacen (1)
- UV-VIS-Spektroskopie (1)
- V-förmige Mesogene (1)
- V-shaped mesogens (1)
- Wasseroxidation (1)
- Wirkmechanismus (1)
- X-ray crystallography (1)
- aqua material (1)
- biaxial nematogens (1)
- biaxiale Nematogene (1)
- biocatalysis (1)
- bioorthogonal (1)
- board-shaped mesogens (1)
- brettförmige Mesogene (1)
- catalysis (1)
- chemical modification (1)
- covalent organic frameworks (1)
- deoxyribozymes (1)
- diketopyrrolopyrroles (1)
- dyes (1)
- electronic and spintronic devices (1)
- electronic devices (1)
- fluorescent protein (1)
- fluorescent resonance energy transfer (1)
- fullerene network (1)
- imines (1)
- in vitro selection (1)
- intervalence charge transfer (1)
- isolation (1)
- large Stokes shift (1)
- luminescent solar concentrators (1)
- metallosupramolecular chemistry (1)
- microtubes (1)
- mode of action (1)
- nucleic acids (1)
- optical spectroscopy (1)
- perylene dyes (1)
- porphyrins (1)
- ribozymes (1)
- ruthenium complexes (1)
- scanning probe microscopy (1)
- structure elucidation (1)
- total synthesis (1)
- transient absorption spectroscopy (1)
- water oxidation (1)
Institute
- Institut für Organische Chemie (20) (remove)
Sonstige beteiligte Institutionen
Temperature-responsive luminescent solar concentrators (LSCs) have been fabricated in which the Förster resonance energy transfer (FRET) between a donor–acceptor pair in a liquid crystalline solvent can be tuned. At room temperatures, the perylene bisimide (PBI) acceptor is aggregated and FRET is inactive; while after heating to a temperature above the isotropic phase of the liquid crystal solvent, the acceptor PBI completely dissolves and FRET is activated. This unusual temperature control over FRET was used to design a color-tunable LSC. The device has been shown to be highly stable towards consecutive heating and cooling cycles, making it an appealing device for harvesting otherwise unused solar energy.
Despite significant progress in the synthesis of covalent organic frameworks (COFs), reports on the precise construction of template-free nano- and microstructures of such materials have been rare. In the quest for dye-containing porous materials, a novel conjugated framework DPP-TAPP-COF with an enhanced absorption capability up to λ=800 nm has been synthesized by utilizing reversible imine condensations between 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP) and a diketopyrrolopyrrole (DPP) dialdehyde derivative. Surprisingly, the obtained COF exhibited spontaneous aggregation into hollow microtubular assemblies with outer and inner tube diameters of around 300 and 90 nm, respectively. A detailed mechanistic investigation revealed the time-dependent transformation of initial sheet-like agglomerates into the tubular microstructures.
Despite their popularity as enzyme engineering targets structural information about Sucrose Phosphorylases remains scarce. We recently clarified that the Q345F variant of Bifidobacterium adolescentis Sucrose Phosphorylase is able to accept large polyphenolic substrates like resveratrol via a domain shift. Here we present a crystal structure of this variant in a conformation suitable for the accommodation of the donor substrate sucrose in excellent agreement with the wild type structure. Remarkably, this conformation does not feature the previously observed domain shift which is therefore reversible and part of a dynamic process rather than a static phenomenon. This crystallographic snapshot completes our understanding of the catalytic cycle of this useful variant and will allow for a more rational design of further generations of Sucrose Phosphorylase variants.
The precise interplay between the mRNA codon and the tRNA anticodon is crucial for ensuring efficient and accurate translation by the ribosome. The insertion of RNA nucleobase derivatives in the mRNA allowed us to modulate the stability of the codon-anticodon interaction in the decoding site of bacterial and eukaryotic ribosomes, allowing an in-depth analysis of codon recognition. We found the hydrogen bond between the N1 of purines and the N3 of pyrimidines to be sufficient for decoding of the first two codon nucleotides, whereas adequate stacking between the RNA bases is critical at the wobble position. Inosine, found in eukaryotic mRNAs, is an important example of destabilization of the codon-anticodon interaction. Whereas single inosines are efficiently translated, multiple inosines, e.g., in the serotonin receptor 5-HT2C mRNA, inhibit translation. Thus, our results indicate that despite the robustness of the decoding process, its tolerance toward the weakening of codon-anticodon interactions is limited.
Self-assembly of multi-stranded perylene dye J-aggregates in columnar liquid-crystalline phases
(2018)
Many discoid dyes self-assemble into columnar liquid-crystalline (LC) phases with packing arrangements that are undesired for photonic applications due to H-type exciton coupling. Here, we report a series of crystalline and LC perylene bisimides (PBIs) self-assembling into single or multi-stranded (two, three, and four strands) aggregates with predominant J-type exciton coupling. These differences in the supramolecular packing and optical properties are achieved by molecular design variations of tetra-bay phenoxy-dendronized PBIs with two N–H groups at the imide positions. The self-assembly is driven by hydrogen bonding, slipped π–π stacking, nanosegregation, and steric requirements of the peripheral building blocks. We could determine the impact of the packing motifs on the spectroscopic properties and demonstrate different J- and H-type coupling contributions between the chromophores. Our findings on structure–property relationships and strong J-couplings in bulk LC materials open a new avenue in the molecular engineering of PBI J-aggregates with prospective applications in photonics.
Understanding relationships between microstructure and electrical transport is an important goal for the materials science of organic semiconductors. Combining high-resolution surface potential mapping by scanning Kelvin probe microscopy (SKPM) with systematic field effect transport measurements, we show that step edges can trap electrons on the surfaces of single crystal organic semiconductors. n-type organic semiconductor crystals exhibiting positive step edge surface potentials display threshold voltages that increase and carrier mobilities that decrease with increasing step density, characteristic of trapping, whereas crystals that do not have positive step edge surface potentials do not have strongly step density dependent transport. A device model and microelectrostatics calculations suggest that trapping can be intrinsic to step edges for crystals of molecules with polar substituents. The results provide a unique example of a specific microstructure–charge trapping relationship and highlight the utility of surface potential imaging in combination with transport measurements as a productive strategy for uncovering microscopic structure–property relationships in organic semiconductors.
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.
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.
Large Stokes shift (LSS) fluorescent proteins (FPs) exploit excited state proton transfer pathways to enable fluorescence emission from the phenolate intermediate of their internal 4 hydroxybenzylidene imidazolone (HBI) chromophore. An RNA aptamer named Chili mimics LSS FPs by inducing highly Stokes-shifted emission from several new green and red HBI analogs that are non-fluorescent when free in solution. The ligands are bound by the RNA in their protonated phenol form and feature a cationic aromatic side chain for increased RNA affinity and reduced magnesium dependence. In combination with oxidative functional-ization at the C2 position of the imidazolone, this strategy yielded DMHBO\(^+\), which binds to the Chili aptamer with a low-nanomolar K\(_D\). Because of its highly red-shifted fluorescence emission at 592 nm, the Chili–DMHBO\(^+\) complex is an ideal fluorescence donor for Förster resonance energy transfer (FRET) to the rhodamine dye Atto 590 and will therefore find applications in FRET-based analytical RNA systems.
In this thesis, the synthesis and photophysics of a great variety of squaraine dyes are presented. This variety is based on four parent squaraines containing either indolenine or quinoline heterocycles. By a suitable choice of the donor and acceptor unit, the optical properties can already be adapted to the properties desired on the stage of the monomer.
To promote a further derivatisation of these dyes, diverse functional groups are attached to the monomers using transition metal-catalysed C-C coupling reactions. However, this has to be preceded by the synthesis of bromine-functionalised derivatives as a direct halogenation of squaraine dyes is not feasible. Therefore, the halogen function is already introduced in precursor molecules giving rise to a molecular building block system containing bromine-, boronic ester-, and alkyne-functionalised monomer units, which pave the way to a plethora of squaraine oligomers and polymers.
The indolenine homopolymer pSQB-1 as well as the corresponding small molecular weight oligomers dSQB-1 and tSQB were synthesized applying Ni-mediated Yamamoto and Pd-catalysed Suzuki coupling methodologies, respectively. The motivation for this project relied on the fundamental investigations by Völker et al. on pSQB-V. A progressive red-shift of the lowest energy absorption maximum from the dimer to the polymer was observed in CHCl3 compared to the monomer. With increasing number of monomer units, the exciton coupling decreases from the dimer to the polymer. In addition, the shape of the absorption band manifold shows a strong dependence on the solvent, which was also observed by Völker et al. J-type aggregate behavior is found in chlorinated solvents such as CHCl3 and DCM, whereas H-type aggregates are formed in acetone. Temperature-dependent absorption studies in PhCN reveals a reversible equilibrium of diverse polymer conformers, which manifests itself in a gradual change from H-aggregate behavior to a mixture with a more pronounced J-aggregate behavior upon raising the temperature. It isassumed that both characteristic aggregate bands correlate in borderline cases with two polymer structures which can be assigned to a zig-zag and a helical structure. As no experimental evidence for these structures could hitherto be provided by NMR, TD-DFT computations on oligomers (22-mers) can reproduce very closely the characteristic features of the spectra for the two conformational isomers.
The subsequent chapters are motivated by the goal to influence the optical properties through a control of the superstructure and thus of the intramolecular aggregate formation.
On the one hand, bulky groups are implemented in the 3-position of the indolenine scaffold to provoke steric repulsion and thus favoring J-aggregate behavior at the expense of helical arrangements. The resulting homopolymer pDiPhSQB bearing two phenyl groups per indolenine exhibits J-type aggregate behavior with red-shifted absorption maxima in all considered solvents which is explained to be caused by the formation of elongated zig-zag structures. Furthermore, single-crystal X-ray analysis of monomer DiPhSQB-2-Br2 reveals a torsion of the indolenine moieties as a consequence of steric congestion. The twist of the molecular geometry and the resulting loss of planarity leads to a serious deterioration of the fluorescence properties, however a significant bathochromic shift of ca. 1 200 cm-1 of the lowest absorption band was observed compared to parent SQB, which is even larger than the shift for dSQB-1 (ca. 1 000 cm-1).
On the other hand, a partial stiffening of the polymer backbone is attempted to create a bias for elongated polymer chains. In this respect, the synthetic approach is to replace every second biarylaxis with the rigid transoid benzodipyrrolenine unit. Despite a rather low average degree of polymerization < 10, exclusively red-shifted absorption maxima are observed in all solvents used.
In order to complete the picture of intramolecular aggregates through the selective design of H-aggregates, a squaraine-squaraine copolymer was synthesised containing the classic cisoid indolenine as well as the cisoid quinoline building block. Taking advantage of the highly structure directing self-assembly character of the quinoline moiety, the copolymer pSQBC indeed showes a broad, blue-shifted main absorption band in comparison with the monomer unit dSQBC. The shape of the absorption band manifold solely exhibited a minor solvent and temperature dependence indicating a persistent H-aggregate behaviour. Hence, as a proof of concept, it is shown that the optical properties of the polymers (H- and J-aggregate) and the corresponding superstructure can be inherently controlled by an adequate design of monomer precursors.
The last chapter of this work deals, in contrast to all other chapters, with intermolecular aggregates. It is shown that the two star-shaped hexasquarainyl benzenes hSQA-1 and hSQA-2 exhibit a strong propensity for self-organisation. Concentration- and temperature-dependent studies reveal a great driving force for self-assembly in acetone. While the larger hSQA-2 instantaneously forms stable aggregates, the aggregates of hSQA-1 shows a pronounced kinetic stability. Taking advantage of the kinetic persistency of these aggregates, the corresponding kinetic activation parameters for aggregation and deaggregation can be assessed. The absorption spectra of both hexasquarainyl benzenes in the aggregated state reveal some striking differences. While hSQA-1 features an intensive, very narrow and blue-shifted absorption band, two red-shifted bands are observed for hSQA-2, which are closely located at the monomer absorption. The very small bandwidth of hSQA-1 are interpreted to be caused by exchange narrowing and pointed towards highly ordered supramolecular aggregates. The concentration-dependent data of the two hexasquarainyl benzenes can be fitted to the dimer-model with excellent correlation coefficients, yielding binding constants in excess of 10^6 M-1, respectively. Such high binding constants are very surprising, considering the unfavourable bulky 3,3-dimethyl groups of the indolenine units which should rather prevent aggregation. Joint theoretical and NMR spectroscopic methods were applied to unravel the supramolecular aggregate structure of hSQA-1, which is shown to consist of two stacked hexasquarainyl benzenes resembling the picture of two stacked bowls.