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Author: Hecht, Stefan × Subject: photochromism ×

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    Mechanistic Insights into the Triplet Sensitized Photochromism of Diarylethenes
    (Weinheim : Wiley-VCH, 2020) Fredrich, Sebastian; Morack, Tobias; Sliwa, Michel; Hecht, Stefan
    Operating photoswitchable molecules repetitively and reliably is crucial for most of their applications, in particular in (opto)electronic devices, and related to reversibility and fatigue resistance, which both critically depend on the photoisomerization mechanism defined by the substitution pattern. Two diarylethene photoswitches bearing biacetyl triplet sensitizers either at the periphery or at the core were investigated using both stationary as well as transient UV/Vis absorption spectroscopy ranging from the femtosecond to the microsecond time scale. The diarylethene with two biacetyl moieties at the periphery is switching predominantly from the triplet excited state, giving rise to an enhanced fatigue resistance. In contrast, the diarylethene bearing one diketone at the photoreactive inner carbon atom cyclizes from the singlet excited state and shows significantly higher quantum yields for both cyclization and cycloreversion. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
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    Highly Cooperative Photoswitching in Dihydropyrene Dimers
    (Weinheim : Wiley-VCH, 2020) Liesfeld, Pauline; Garmshausen, Yves; Budzak, Simon; Becker, Jonas; Dallmann, Andre; Jacquemin, Denis; Hecht, Stefan
    We present a strategy to achieve highly cooperative photoswitching, where the initial switching event greatly facilitates subsequent switching of the neighboring unit. By linking donor/acceptor substituted dihydropyrenes via suitable π-conjugated bridges, the quantum yield of the second photochemical ring-opening process could be enhanced by more than two orders of magnitude as compared to the first ring-opening. As a result, the intermediate mixed switching state is not detected during photoisomerization although it is formed during the thermal back reaction. Comparing the switching behavior of various dimers, both experimentally and computationally, helped to unravel the crucial role of the bridging moiety connecting both photochromic units. The presented dihydropyrene dimer serves as model system for longer cooperative switching chains, which, in principle, should enable efficient and directional transfer of information along a molecularly defined path. Moreover, our concept allows to enhance the photosensitivity in oligomeric and polymeric systems and materials thereof. © 2020 The Authors. Published by Wiley-VCH GmbH