The effect of substitution of 3-chrysenyl group (Ar) on unsaturated double bonds in their triplet sensitized isomerization was investigated for Ar–CH=CH–R, R=′Bu (BC) and Ph (SC) by means of stationary irradiations, laser flash photolyses, and MO calculations. Both olefins undergo mutual isomerization between their cis- and trans-isomers. However, BC has a unique triplet energy surface with two decay funnels at the planar trans (3t*) and twisted (3p*) conformations, which are in equilibrium with each other; 3t* undergoes either unimolecular decay to the ground-state trans isomer or triplet energy transfer to the cis isomer (quantum chain process) and 3p* decays to the ground state to give the cis and trans isomers. Tn←T1 absorptions observed for BC and SC are mainly attributed to 3t* and 3p*, respectively, on the basis of semiempirical MO calculations. The populations at 3t* and 3p* are estimated.
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Karatsu et al. (1991) studied this question.
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