An abinitio study of the photochemistry of azobenzene

Abstract

The photochemistry under n→π* and π→π* excitation and the thermal isomerization of azobenzene are studied by a theoretical approach. Two mechanisms are considered: torsion around the N2N double bond and the inversion of one N atom. We optimize the most important geometries with CASSCF and we calculate the potential energy curves for the lowest states (4 singlets and 2 triplets) with multireference perturbation theory. Our calculations support the current view that inversion is the preferred pathway for ground state isomerization and probably also by n→π* excitation, while torsion occurs by π→π* excitation. We find that two states, 2¹A and 2¹B in C₂ symmetry, are important in the π→π* photochemistry.

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