Photochemical Cis to Trans One-Way Isomerization of Styrylazulenes on Their Triplet Excited State. Examination of Ethylenes with Non-Benzenoid Substituents of Low Triplet Energies

Article abstract of DOI:10.1246/bcsj.67.1674

1-Styrylazulene and 7-isopropyl-1,4-dimethyl-3-styrylazulene (3-styrylguaiazulene) underwent one-way isomerization from the cis to the trans isomer on triplet sensitization.Their triplet states as intermediates of the isomerization were observed by laser flash photolysis.However, their excitation to either the lowest excited single state (S₁) or the second excited singlet state (S₂) by direct irradiation afforded photostationary mixtures comprising 98percent of the trans and 2percent the cis isomers, which implies the participation of a singlet isomerization path.