@article{LiuVonhausenSchulzetal.2022, author = {Liu, Bin and Vonhausen, Yvonne and Schulz, Alexander and H{\"o}bartner, Claudia and W{\"u}rthner, Frank}, title = {Peptide Backbone Directed Self-Assembly of Merocyanine Oligomers into Duplex Structures}, series = {Angewandte Chemie International Edition}, volume = {61}, journal = {Angewandte Chemie International Edition}, number = {21}, doi = {10.1002/anie.202200120}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-318797}, year = {2022}, abstract = {The pseudopeptide backbone provided by N-(2-aminoethyl)-glycine oligomers with attached nucleobases has been widely utilized in peptide nucleic acids (PNAs) as DNA mimics. Here we demonstrate the suitability of this backbone for the formation of structurally defined dye stacks. Toward this goal a series of peptide merocyanine (PMC) dye oligomers connected to a N-(2-aminoethyl)-glycine backbone were prepared through peptide synthesis. Our concentration-, temperature- and solvent-dependent UV/Vis absorption studies show that under the control of dipole-dipole interactions, smaller-sized oligomers consisting of one, two or three dyes self-assemble into defined duplex structures containing two up to six chromophores. In contrast, upon further extension of the oligomer, the chosen peptide backbone cannot direct the formation of a defined duplex architecture anymore due to intramolecular aggregation between the dyes. For all aggregate species a moderate aggregation-induced emission enhancement is observed.}, language = {en} } @article{SchulzWuerthner2022, author = {Schulz, Alexander and W{\"u}rthner, Frank}, title = {Folding-induced fluorescence enhancement in a series of merocyanine hetero-folda-trimers}, series = {Angewandte Chemie International Edition}, volume = {61}, journal = {Angewandte Chemie International Edition}, number = {2}, doi = {10.1002/anie.202114667}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256582}, year = {2022}, abstract = {Many dyes suffer from fast non-radiative decay pathways, thereby showing only short-lived excited states and weak photoluminescence. Here we show a pronounced fluorescence enhancement for a weakly fluorescent merocyanine (MC) dye by being co-facially stacked to other dyes in hetero-folda-trimer architectures. By means of fluorescence spectroscopy (lifetime, quantum yield) the fluorescence enhancement was explained by the rigidification of the emitting chromophore in the defined foldamer architecture and the presence of a non-forbidden lowest exciton state in H-coupled hetero-aggregates. This folding-induced fluorescence enhancement (FIFE) for specific sequences of π-stacked dyes points at a viable strategy toward improved fluorophores that relates to the approach used by nature in the green fluorescent protein (GFP).}, language = {en} } @article{HocheSchulzDietrichetal.2019, author = {Hoche, Joscha and Schulz, Alexander and Dietrich, Lysanne Monika and Humeniuk, Alexander and Stolte, Matthias and Schmidt, David and Brixner, Tobias and W{\"u}rthner, Frank and Mitric, Roland}, title = {The origin of the solvent dependence of fluorescence quantum yields in dipolar merocyanine dyes}, series = {Chemical Science}, volume = {10}, journal = {Chemical Science}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-198707}, pages = {11013}, year = {2019}, abstract = {Fluorophores with high quantum yields are desired for a variety of applications. Optimization of promising chromophores requires an understanding of the non-radiative decay channels that compete with the emission of photons. We synthesized a new derivative of the famous laser dye 4-dicyanomethylen-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM),i.e., merocyanine 4-(dicyanomethylene)-2-tert-butyl-6-[3-(3-butyl-benzothiazol-2-ylidene)1-propenyl]-4H-pyran (DCBT). We measured fluorescence lifetimes and quantum yields in a variety of solvents and found a trend opposite to the energy gap law.This motivated a theoretical investigation into the possible non-radiative decay channels. We propose that a barrier to a conical intersection exists that is very sensitive to the solvent polarity. The conical intersection is characterized by a twisted geometry which allows a subsequent photoisomerization. Transient absorption measurements confirmed the formation of a photoisomer in unpolar solvents, while the measurements of fluorescence quantum yields at low temperature demonstrated the existence of an activation energy barrier.}, language = {en} } @unpublished{AuerhammerSchulzSchmiedeletal.2019, author = {Auerhammer, Nina and Schulz, Alexander and Schmiedel, Alexander and Holzapfel, Marco and Hoche, Joscha and R{\"o}hr, Merle I. S. and Mitric, Roland and Lambert, Christoph}, title = {Dynamic exciton localisation in a pyrene-BODIPY-pyrene dye conjugate}, series = {Physical Chemistry Chemical Physics}, journal = {Physical Chemistry Chemical Physics}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-198718}, year = {2019}, abstract = {The photophysics of a molecular triad consisting of a BODIPY dye and two pyrene chromophores attached in 2-position are investigated by steady state and fs-time resolved transient absorption spectroscopy as well as by field induced surface hopping (FISH) simulations. While the steady state measurements indicate moderate chromophore interactions within the triad, the time resolved measurements show upon pyrene excitation a delocalised excited state which localises onto the BODIPY chromophore with a time constant of 0.12 ps. This could either be interpreted as an internal conversion process within the excitonically coupled chromophores or as an energy transfer from the pyrenes to the BODIPY dye. The analysis of FISH-trajectories reveals an oscillatory behaviour where the excitation hops between the pyrene units and the BODIPY dye several times until finally they become localised on the BODIPY chromophore within 100 fs. This is accompanied by an ultrafast nonradiative relaxation within the excitonic manifold mediated by the nonadiabatic coupling. Averaging over an ensemble of trajectories allowed us to simulate the electronic state population dynamics and determine the time constants for the nonradiative transitions that mediate the ultrafast energy transfer and exciton localisation on BODIPY.}, language = {en} }