UNUSUAL BEHAVIOUR OF β- tert -ALKYLSTYRENES IN PHOTOSENSITIZED CIS–TRANS ISOMERIZATION. STRUCTURAL EFFECTS ON TRIPLET ENERGY TRANSFER

Photostationary state isomer ratios, rate constants for triplet energy transfer, and quantum yields of isomerization were determined for the triplet sensitized isomerization of β-alkylstyrenes (PhCH=CHR, R = CH3, CH2CH3, CH(CH3)2, C(CH3)3, and C(CH3)2CH2CH3) in benzene. The remarkably high ratio of cis-tert-alkylstyrenes at the photostationary state is mainly attributed to lower rate constants for energy transfer to cis-isomers than to trans-isomers.