Solvent-driven adiabatic trans-to-cis photoisomerization of 4-styrylquinoline

Direct one-stage photocyclization of trans-4-styrylquinoline to dihydrobenzo[i]phenanthridine (DHBP) in n-hexane with a quantum yield of 0.013 was observed. The kinetics of the photochemical transformations and an effect of the excitation intensity on the yield of DHBP were studied. In ethanol photocyclization proceeded in two stages with intermediate formation of the cis-isomer in the ground state. These facts imply a diabatic reaction pathway for trans-to-cis photoisomerization of 4-styrylquinoline in ethanol and an adiabatic pathway in hexane.