Cooperating Dinitrogen and Phenyl Rotations in trans-Azobenzene Photoisomerization

Semiempirical OM2/MRCI surface-hopping simulations have been performed to study the trans-to-cis photoisomerization of azobenzene upon excitation to the S1 state. The decay dynamics to the ground state shows an oscillatory pattern that can be attributed to an out-of-plane rotation of the N2 moiety. The reaction is thus initially driven by N2 rotation which triggers phenyl rotations around the C–N bonds. The cis isomer is produced most effectively when the phenyl rings rotate in phase. Mode-specific excitations cause variations in the computed decay times and product yields