Photoisomerization and Photocyclization Reactions of 1-Styrylanthracene

Article abstract of DOI:10.1246/bcsj.68.920

On triplet sensitization, 1-styrylanthracene (1SA) undergoes adiabatic cis->trans one-way isomerization (³c^*->³t^*) similarly to 2-anthrylethylenes.However, upon direct irradiation, cis-1SA in the singlet excited state mostly undergoes cyclization to a dihydrophenanthrene-type product (DHP), 4a,4b-dihydrobenzochrysene, competing with an inefficient intersystem crossing to ³c^* followed by one-way isomerization.The produced DHP, in deaerated benzene, is reverted to cis-1SA by a thermal (E_a = 14.9 kcal mol^-1) or a photochemical pathway; however, under an oxygenated atmosphere DHP gives benzochrysene.A failure in the production of a cyclized product upon the excitation of trans-1SA shows that the isomerization really takes place in a one-way fashion.