Photophysically relevant potential energy functions of low-lying singlet states of benzene, pyridine and pyrazine: an ab initio study

Potential energy functions of low-lying singlet states of benzene, pyridine, and pyrazine along the reaction path leading to the prefulvenic forms have been calculated with the UHF/STO-3G method. It is found that the electronic ground state of the prefulvenic form is adiabatically correlated to a valence excitation of the aromatic ring at the planar configuration (the S₁ state in benzene, the S₂ state in pyridine and pyrazine). Some consequences for the photophysical dynamics (channel-three-like behaviour) of azabenzenes are discussed.