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Cyclohexenylphenyldiazene:  A Simple Surrogate of the Azobenzene Photochromic Unit

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journal contribution
posted on 21.03.2007, 00:00 by Irene Conti, Filippo Marchioni, Alberto Credi, Giorgio Orlandi, Goffredo Rosini, Marco Garavelli
We have carried out an experimental and computational study on the ground- and excited-state photochemical and photophysical properties of (1-cyclohexenyl)phenyldiazene (CPD), a species formally derived from azobenzene in which one of the phenyl rings is replaced by a 1-cyclohexene substituent. The results show that CPD does substantially behave like azobenzene, but with a higher (∼70%) ΦZE (nπ*) photoisomerization quantum yield, calling for CPD as an effective alternative of azobenzene itself with new functionalization possibilities. By use of state-of-the-art ab initio CASPT2//CASSCF minimum energy path computations, we have identified the most efficient decay and isomerization routes of the absorbing singlet (ππ*), S1 (nπ*), T1, and S0 states of CPD. The resulting mechanistic scheme agrees with experimental findings and provides a rationale of the observed photoisomerization quantum yields. Furthermore, this study provides a deep insight on the photophysical and photochemical properties of compounds based on the −NN− double bond which supplies a general model for the photoreactivity of azobenzene-type compounds in general. This is expected to be a useful guideline for the design of novel photoreactive azo compounds.