Correlation between Absorption and Substitution of Photochromic 1,2-Bis(thienyl)ethenes (BTEs) Using Modified Spectroscopic Hammett Equations |
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Authors: | Sven Nagorny Thea Weingartz Dr Jan C Namyslo Prof Dr Jörg Adams Prof Dr Andreas Schmidt |
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Institution: | 1. Clausthal University of Technology, Institute of Organic Chemistry, Leibnizstraße 6, D-38678 Clausthal-Zellerfeld, Germany;2. Clausthal University of Technology, Institute of Physical Chemistry, Arnold-Sommerfeld-Straße 4, 38678 Clausthal-Zellerfeld, Germany |
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Abstract: | Series of photochromic 1,2-bis(thienyl)ethenes possessing perfluorocyclopentene backbones, either hydrogen or methyl groups at the β-positions of the thiophenes, and a variety of substituents in their α'-positions were prepared, which cover the range from electron-donating to electron-withdrawing (Me, −CH2OH, −OTBS, −TMS, −Br, 1,3-dioxan-2-yl, pyridin-4-yl, −CH2OH, −COOH). As a linear free energy relationship the spectroscopic Hammett equation gives fair to excellent fits to the excitation energy of the absorption maxima of the ring-opened as well as the ring-closed forms of the BTEs, when Hammett substituent constants σp were replaced by Brown's modified substituent constants σp+ and σp−. Vice versa, hitherto unknown Hammett-Brown substituent constants can be estimated from the UV spectra. Furthermore, we compared the experimentally measured absorption maxima with values which we calculated by three different methods (DFT STEOM-DLPNO-CCSD/def2-TZVPP, TD-DFT ωB97X-D3/6-31G*, TD-DFT ωB97X-D3/6-311++G**). |
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Keywords: | Diarylethene Linear free energy Photochromic Spectroscopic Hammett equation Switchable molecules |
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