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Excited‐State Decay in the Photoisomerisation of Azobenzene: A New Balance between Mechanisms
Author(s) -
Casellas Josep,
Bearpark Michael J.,
Reguero Mar
Publication year - 2016
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201600502
Subject(s) - conical intersection , excited state , relaxation (psychology) , ab initio , excitation , chemistry , ab initio quantum chemistry methods , ground state , singlet state , conical surface , molecular physics , planar , atomic physics , potential energy , physics , materials science , molecule , quantum mechanics , psychology , social psychology , computer graphics (images) , organic chemistry , computer science , composite material
The mechanism of the photoisomerisation of azobenzene has been studied by means of multiconfigurational ab initio calculations. Our results show that it is necessary to account for the dynamic electron correlation in the location of the critical points (CASPT2 optimizations) to obtain a correct description of the topography of the potential energy surfaces of the low energy singlet excited states. By using this methodology, we have found that the state populated by the initial excitation is the S 2 (ππ*) state, which decays very efficiently to the S 1 (nπ*) state at a pedal‐like non‐rotated geometry. In the S 1 state, relaxation leads to a rotated geometry where the system decays to the ground state, in which further relaxation can lead to either the trans or cis geometries. However, the S 1 /S 0 conical intersection seam also extends to planar geometries, so this reaction path is also accessible for rotation‐constrained systems. Our results explain the experimental observations satisfactorily.