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Can Diarylethene Photochromism Be Explained by a Reaction Path Alone? A CASSCF Study with Model MMVB Dynamics

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posted on 18.12.2003, 00:00 by Martial Boggio-Pasqua, Marcella Ravaglia, Michael J. Bearpark, Marco Garavelli, Michael A. Robb
The origin of the photochromic properties of diarylethenes is a conical intersection (which we have located computationally), but we show that dynamics calculations are necessary to explain why the conical intersection is accessible, because the excited-state reaction path is not contained in the branching space defining the intersection. Four different systems have been studied:  1,2-di(3-furyl)ethene, 1,2-di(3-thienyl)ethene, 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene, and a model hydrocarbon system. Critical points on the ground- and excited-state potential energy surfaces were calculated using complete active space self-consistent field (CASSCF) theory; dynamics calculations were carried out using the molecular mechanics−valence bond (MMVB) method. The main experimental observations (i.e., picosecond time domain, quantum yield, temperature dependence, and fluorescence) can be interpreted on the basis of our results.

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