TY  - JOUR
A1  - Schulz, Alexander
A1  - Würthner, Frank
T1  - Folding-induced fluorescence enhancement in a series of merocyanine hetero-folda-trimers
JF  - Angewandte Chemie International Edition
N2  - 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).
KW  - organic chemistry
KW  - merocyanines
KW  - aggregation
KW  - dyes/pigments
KW  - fluorescence
KW  - folding
Y1  - 2022
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256582
VL  - 61
IS  - 2
ER  - 
TY  - JOUR
A1  - Bold, Kevin
A1  - Stolte, Matthias
A1  - Shoyama, Kazutaka
A1  - Holzapfel, Marco
A1  - Schmiedel, Alexander
A1  - Lambert, Christoph
A1  - Würthner, Frank
T1  - Macrocyclic donor-acceptor dyads composed of a perylene bisimide dye surrounded by oligothiophene bridges
JF  - Angewandte Chemie Internationale Edition
N2  - Two macrocyclic architectures comprising oligothiophene strands that connect the imide positions of a perylene bisimide (PBI) dye have been synthesized via a platinum-mediated cross-coupling strategy. The crystal structure of the double bridged PBI reveals all syn-arranged thiophene units that completely enclose the planar PBI chromophore via a 12-membered macrocycle. The target structures were characterized by steady-state UV/Vis absorption, fluorescence and transient absorption spectroscopy, as well as cyclic and differential pulse voltammetry. Both donor–acceptor dyads show ultrafast Förster Resonance Energy Transfer and photoinduced electron transfer, thereby leading to extremely low fluorescence quantum yields even in the lowest polarity cyclohexane solvent.
KW  - organic chemistry
KW  - photoinduced electron transfer
KW  - donor–acceptor dyads
KW  - macrocycles
KW  - oligothiophenes
KW  - perylenebisimide
Y1  - 2022
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256569
VL  - 61
IS  - 1
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  -