TY - JOUR A1 - Spenst, Peter A1 - Young, Ryan M. A1 - Wasielewski, Michael R. A1 - Würthner, Frank T1 - Guest and solvent modulated photo-driven charge separation and triplet generation in a perylene bisimide cyclophane JF - Chemical Science N2 - Cofacial positioning of two perylene bisimide (PBI) chromophores at a distance of 6.5 angstrom in a cyclophane structure prohibits the otherwise common excimer formation and directs photoexcited singlet state relaxation towards intramolecular symmetry-breaking charge separation (τ\(_{CS}\) = 161 +/- 4 ps) in polar CH\(_2\)Cl\(_2\), which is thermodynamically favored with a Gibbs free energy of ΔG\(_{CS}\) = -0.32 eV. The charges then recombine slowly in τ\(_{CR}\) = 8.90 +/- 0.06 ns to form the PBI triplet excited state, which can be used subsequently to generate singlet oxygen in 27% quantum yield. This sequence of events is eliminated by dissolving the PBI cyclophane in non-polar toluene, where only excited singlet state decay occurs. In contrast, complexation of electron-rich aromatic hydrocarbons by the host PBI cyclophane followed by photoexcitation of PBI results in ultrafast electron transfer (<10 ps) from the guest to the PBI in CH\(_2\)Cl\(_2\). The rate constants for charge separation and recombination increase as the guest molecules become easier to oxidize, demonstrating that charge separation occurs close to the peak of the Marcus curve and the recombination lies far into the Marcus inverted region. KW - photoinduced electron transfer KW - Marcus inverted region KW - cyclic perylene bisimide KW - PBI cyclophane Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-191252 VL - 7 IS - 8 ER - TY - JOUR A1 - Plötz, P.-A. A1 - Polyutov, S. P. A1 - Ivanov, S. D. A1 - Fennel, F. A1 - Wolter, S. A1 - Niehaus, T. A1 - Xie, Z. A1 - Lochbrunner, S. A1 - Würthner, Frank A1 - Kühn, O. T1 - Biphasic aggregation of a perylene bisimide dye identified by exciton-vibrational spectra JF - Physical Chemistry Chemical Physics N2 - The quantum efficiency of light emission is a crucial parameter of supramolecular aggregates that can be tuned by the molecular design of the monomeric species. Here, we report on a strong variation of the fluorescence quantum yield due to different phases of aggregation for the case of a perylene bisimide dye. In particular, a change of the dominant aggregation character from H- to J-type within the first aggregation steps is found, explaining the observed dramatic change in quantum yield. This behaviour is rationalised by means of a systematic study of the intermolecular potential energy surfaces using the time-dependent density functional based tight-binding (TD-DFTB) method. This provides a correlation between structural changes and a coupling strength and supports the notion of H- type stacked dimers and J-type stack-slipped dimers. The exciton-vibrational level structure is modelled by means of an excitonic dimer model including two effective vibrational modes per monomer. Calculated absorption and fluorescence spectra are found to be in reasonable agreement with experimental ones, thus supporting the conclusion on the aggregation behaviour. KW - Potential-energy curves KW - Simulations KW - Molecular-dynamics KW - Systems KW - Fluorescence KW - Sracking KW - Pathway KW - Dimers KW - State Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-187387 VL - 18 IS - 36 ER - TY - JOUR A1 - Gershberg, Jana A1 - Fennel, Franziska A1 - Rehm, Thomas H. A1 - Lochbrunner, Stefan A1 - Würthner, Frank T1 - Anti-cooperative supramolecular polymerization: a new K\(_2\)-K model applied to the self-assembly of perylene bisimide dye proceeding via well-defined hydrogen-bonded dimers JF - Chemical Science N2 - A perylene bisimide dye bearing amide functionalities at the imide positions derived from amino acid L-alanine and a dialkoxy-substituted benzyl amine self-assembles into tightly bound dimers by π-π-stacking and hydrogen bonding in chloroform. In less polar or unpolar solvents like toluene and methylcyclohexane, and in their mixtures, these dimers further self-assemble into extended oligomeric aggregates in an anti-cooperative process in which even numbered aggregates are highly favoured. The stepwise transition from dimers into oligomers can not be properly described by conventional K\(_2\)-K model, and thus a new K\(_2\)-K aggregation model has been developed, which interpretes the present anti-cooperative supramolecular polymerization more appropriately. The newly developed K\(_2\)-K model will be useful to describe self-assembly processes of a plethora of other π-conjugated molecules that are characterized by a favored dimer species. KW - π–π Stacking KW - nucleation elongation KW - upramolecular polymerization process KW - dimerization KW - K2–K model Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-191428 VL - 7 IS - 3 ER - TY - JOUR A1 - Görl, Daniel A1 - Soberats, Bartolome A1 - Herbst, Stefanie A1 - Stepanenko, Vladimir A1 - Würthner, Frank T1 - Perylene bisimide hydrogels and lyotropic liquid crystals with temperature-responsive color change JF - Chemical Science N2 - The self-assembly of perylene bisimide (PBI) dyes bearing oligo ethylene glycol (OEG) units in water affords responsive functional nanostructures characterized by their lower critical solution temperature (LCST). Tuning of the LCST is realized by a supramolecular approach that relies on two structurally closely related PBI–OEG molecules. The two PBIs socially co-assemble in water and the resulting nanostructures exhibit a single LCST in between the transition temperatures of the aggregates formed by single components. This permits to precisely tune the transition from a hydrogel to a lyotropic liquid crystal state at temperatures between 26 and 51 °C by adjusting the molar fraction of the two PBIs. Owing to concomitant changes in PBI–PBI interactions this phase transition affords a pronounced color change with “fluorescence-on” response that can be utilized as a smart temperature sensory system. KW - perylene bisimide hydrogels Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-162459 VL - 7 IS - 11 ER - TY - JOUR A1 - Bialas, David A1 - Zitzler-Kunkel, André A1 - Kirchner, Eva A1 - Schmidt, David A1 - Würthner, Frank T1 - Structural and quantum chemical analysis of exciton coupling in homo- and heteroaggregate stacks of merocyanines JF - Nature Communications N2 - Exciton coupling is of fundamental importance and determines functional properties of organic dyes in (opto-)electronic and photovoltaic devices. Here we show that strong exciton coupling is not limited to the situation of equal chromophores as often assumed. Quadruple dye stacks were obtained from two bis(merocyanine) dyes with same or different chromophores, respectively, which dimerize in less-polar solvents resulting in the respective homo- and heteroaggregates. The structures of the quadruple dye stacks were assigned by NMR techniques and unambiguously confirmed by single-crystal X-ray analysis. The heteroaggregate stack formed from the bis(merocyanine) bearing two different chromophores exhibits remarkably different ultraviolet/vis absorption bands compared with those of the homoaggregate of the bis(merocyanine) comprising two identical chromophores. Quantum chemical analysis based on an extension of Kasha’s exciton theory appropriately describes the absorption properties of both types of stacks revealing strong exciton coupling also between different chromophores within the heteroaggregate. KW - exciton coupling KW - merocyanines KW - quantum chemical analysis Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-170200 VL - 7 ER - TY - JOUR A1 - Seifert, Sabine A1 - Shoyama, Kazutaka A1 - Schmidt, David A1 - Würthner, Frank T1 - An electron-poor C\(_{64}\) nanographene by palladium-catalyzed cascade C-C bond formation: one-pot synthesis and single-crystal structure analysis JF - Angewandte Chemie-International Edition N2 - Herein, we report the one-pot synthesis of an electron-poor nanographene containing dicarboximide groups at the corners. We efficiently combined palladium-catalyzed Suzuki-Miyaura cross-coupling and dehydrohalogenation to synthesize an extended two-dimensional pi-scaffold of defined size in a single chemical operation starting from N-(2,6-diisopropylphenyl)-4,5-dibromo-1,8-naphthalimide and a tetrasubstituted pyrene boronic acid ester as readily accessible starting materials. The reaction of these precursors under the conditions commonly used for Suzuki-Miyaura cross-coupling afforded a C\(_{64}\) nanographene through the formation of ten C-C bonds in a one-pot process. Single-crystal X-ray analysis unequivocally confirmed the structure of this unique extended aromatic molecule with a planar geometry. The optical and electrochemical properties of this largest ever synthesized planar electron-poor nanographene skeleton were also analyzed. KW - Graphene nanoribbons KW - Liquid-crystalline KW - dyes/pigments KW - polycyclic aromatic hydrocarbons KW - two-dimensional nanostructures KW - Aromatic-hydrocarbon KW - Carbon KW - Dyes KW - Functionalization KW - cascade reactions KW - nanographene Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-188889 VL - 55 IS - 22 ER -