Triplet Intermediates in Cis-Trans Photoisomerization of 3-Chrysenylethylenes

Article abstract of DOI:10.1246/bcsj.64.3355

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 = ^tBu (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.T_n <- 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.