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 - THES A1 - Bialas, David T1 - Exciton Coupling in Homo- and Heterostacks of Merocyanine and Perylene Bisimide Dyes T1 - Exzitonenkopplung in Homo- und Hererostapel von Merocyanin- und Perylenbisimidfarbstoffen N2 - In the present thesis it could be demonstrated that strong exciton coupling does not only occur between same type of chromophores but also between chromophores with different excited state energies. The coupling significantly influences the optical absorption properties of the heterostacks comprising merocyanine and perylene bisimide dyes, respectively, and is an indication for coherent energy transfer between the chromophores. In addition, bis(merocyanine)-C60 conjugates have been synthesized, which self-assemble in non-polar solvents resulting in well-defined supramolecular p/n-heterojunctions in solution. These model systems enabled femtosecond transient absorption studies on the photoinduced electron transfer process, which is a key step for the formation of charge carriers in organic solar cells. N2 - In der vorliegenden Doktorarbeit konnte gezeigt werden, dass eine starke Exzitonenkopplung nicht nur zwischen gleichen Chromophoren, sondern auch zwischen Chromophoren mit unterschiedlichen Energien der angeregten Zustände möglich ist. Diese beeinflusst maßgeblich die Absorptionsspektren der Heterostapel bestehend aus Merocyanin- bzw. Perylenbisimidfarbstoffen und deutet außerdem auf einen kohärenten Energientransfer zwischen den Chromophoren hin. Weiterhin wurden Bis(merocyanin)-C60-Konjugate synthetisiert, die in unpolaren Lösungsmitteln selbst assemblieren und auf diese Weise wohldefinierte supramolekulare p/n-Heterogrenzflächen gebildet werden. An diesen wurde mithilfe von femtosekundenaufgelöster transienter Absorptionsspektroskopie der photoinduzierte Elektronentransfer untersucht, was ein wichtiger Schritt bei der Erzeugung von Ladungsträgern in organischen Solarzellen darstellt. KW - Exziton KW - Supramolekulare Chemie KW - Perylenderivate KW - Exciton Coupling KW - Heteroaggregates KW - Supramolecular Chemistry KW - Merocyanine KW - Aggregat KW - Exzitonenkopplung KW - Heteroaggregate Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-152418 ER - TY - JOUR A1 - Dietzsch, Julia A1 - Bialas, David A1 - Bandorf, Johannes A1 - Würthner, Frank A1 - Höbartner, Claudia T1 - Tuning Exciton Coupling of Merocyanine Nucleoside Dimers by RNA, DNA and GNA Double Helix Conformations JF - Angewandte Chemie International Edition N2 - Exciton coupling between two or more chromophores in a specific environment is a key mechanism associated with color tuning and modulation of absorption energies. This concept is well exemplified by natural photosynthetic proteins, and can also be achieved in synthetic nucleic acid nanostructures. Here we report the coupling of barbituric acid merocyanine (BAM) nucleoside analogues and show that exciton coupling can be tuned by the double helix conformation. BAM is a nucleobase mimic that was incorporated in the phosphodiester backbone of RNA, DNA and GNA oligonucleotides. Duplexes with different backbone constitutions and geometries afforded different mutual dye arrangements, leading to distinct optical signatures due to competing modes of chromophore organization via electrostatic, dipolar, - stacking and hydrogen-bonding interactions. The realized supramolecular motifs include hydrogenbonded BAM–adenine base pairs and antiparallel as well as rotationally stacked BAM dimer aggregates with distinct absorption, CD and fluorescence properties. KW - Chromophore Assembly KW - Merocyanine KW - Nucleobase Analogue KW - Supramolecular Element KW - Nucleic Acids Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-254565 ER - TY - JOUR A1 - Kim, Jin Hong A1 - Schembri, Tim A1 - Bialas, David A1 - Stolte, Matthias A1 - Würthner, Frank T1 - Slip‐Stacked J‐Aggregate Materials for Organic Solar Cells and Photodetectors BT - This paper is dedicated to Prof. Daoben Zhu on the occasion of his 80th birthday JF - Advanced Materials N2 - Dye–dye interactions affect the optical and electronic properties in organic semiconductor films of light harvesting and detecting optoelectronic applications. This review elaborates how to tailor these properties of organic semiconductors for organic solar cells (OSCs) and organic photodiodes (OPDs). While these devices rely on similar materials, the demands for their optical properties are rather different, the former requiring a broad absorption spectrum spanning from the UV over visible up to the near‐infrared region and the latter an ultra‐narrow absorption spectrum at a specific, targeted wavelength. In order to design organic semiconductors satisfying these demands, fundamental insights on the relationship of optical properties are provided depending on molecular packing arrangement and the resultant electronic coupling thereof. Based on recent advancements in the theoretical understanding of intermolecular interactions between slip‐stacked dyes, distinguishing classical J‐aggregates with predominant long‐range Coulomb coupling from charge transfer (CT)‐mediated or ‐coupled J‐aggregates, whose red‐shifts are primarily governed by short‐range orbital interactions, is suggested. Within this framework, the relationship between aggregate structure and functional properties of representative classes of dye aggregates is analyzed for the most advanced OSCs and wavelength‐selective OPDs, providing important insights into the rational design of thin‐film optoelectronic materials. KW - crystal engineering KW - exciton coupling KW - J‐aggregates KW - organic photodiodes KW - organic solar cells Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-276537 VL - 34 IS - 22 ER - TY - JOUR A1 - Kim, Jin Hong A1 - Liess, Andreas A1 - Stolte, Matthias A1 - Krause, Ana-Maria A1 - Stepanenko, Vladimir A1 - Zhong, Chuwei A1 - Bialas, David A1 - Spano, Frank A1 - Würthner, Frank T1 - An Efficient Narrowband Near-Infrared at 1040 nm Organic Photodetector Realized by Intermolecular Charge Transfer Mediated Coupling Based on a Squaraine Dye JF - Advanced Materials N2 - A highly sensitive short-wave infrared (SWIR, λ > 1000 nm) organic photodiode (OPD) is described based on a well-organized nanocrystalline bulk-heterojunction (BHJ) active layer composed of a dicyanovinyl-functionalized squaraine dye (SQ-H) donor material in combination with PC\(_{61}\)BM. Through thermal annealing, dipolar SQ-H chromophores self-assemble in a nanoscale structure with intermolecular charge transfer mediated coupling, resulting in a redshifted and narrow absorption band at 1040 nm as well as enhanced charge carrier mobility. The optimized OPD exhibits an external quantum efficiency (EQE) of 12.3% and a full-width at half-maximum of only 85 nm (815 cm\(^{-1}\)) at 1050 nm under 0 V, which is the first efficient SWIR OPD based on J-type aggregates. Photoplethysmography application for heart-rate monitoring is successfully demonstrated on flexible substrates without applying reverse bias, indicating the potential of OPDs based on short-range coupled dye aggregates for low-power operating wearable applications. KW - squaraine dyes KW - crystal engineering KW - J-aggregates KW - near-infrared sensitivity KW - organic photodiodes Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256374 VL - 33 IS - 26 ER - TY - JOUR A1 - Shen, Chia-An A1 - Bialas, David A1 - Hecht, Markus A1 - Stepanenko, Vladimir A1 - Sugiyasu, Kazunori A1 - Würthner, Frank T1 - Polymorphism in squaraine dye aggregates by self-assembly pathway differentiation: panchromatic tubular dye nanorods versus J-aggregate nanosheets JF - Angewandte Chemie International Edition N2 - A bis(squaraine) dye equipped with alkyl and oligoethyleneglycol chains was synthesized by connecting two dicyanomethylene substituted squaraine dyes with a phenylene spacer unit. The aggregation behavior of this bis(squaraine) was investigated in non-polar toluene/tetrachloroethane (98:2) solvent mixture, which revealed competing cooperative self-assembly pathways into two supramolecular polymorphs with entirely different packing structures and UV/Vis/NIR absorption properties. The self-assembly pathway can be controlled by the cooling rate from a heated solution of the monomers. For both polymorphs, quasi-equilibrium conditions between monomers and the respective aggregates can be established to derive thermodynamic parameters and insights into the self-assembly mechanisms. AFM measurements revealed a nanosheet structure with a height of 2 nm for the thermodynamically more stable polymorph and a tubular nanorod structure with a helical pitch of 13 nm and a diameter of 5 nm for the kinetically favored polymorph. Together with wide angle X-ray scattering measurements, packing models were derived: the thermodynamic polymorph consists of brick-work type nanosheets that exhibit red-shifted absorption bands as typical for J-aggregates, while the nanorod polymorph consists of eight supramolecular polymer strands of the bis(squaraine) intertwined to form a chimney-type tubular structure. The absorption of this aggregate covers a large spectral range from 550 to 875 nm, which cannot be rationalized by the conventional exciton theory. By applying the Essential States Model and considering intermolecular charge transfer, the aggregate spectrum was adequately reproduced, revealing that the broad absorption spectrum is due to pronounced donor-acceptor overlap within the bis(squaraine) nanorods. The latter is also responsible for the pronounced bathochromic shift observed for the nanosheet structure as a result of the slip-stacked arranged squaraine chromophores. KW - organic chemistry KW - supramolecular polymers KW - nanorods and nanosheets KW - polymorphism KW - squaraine dyes KW - cooperative self-assembly Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256443 IS - 21 ET - 60 ER -