Unveiling the Mechanism for the Photochemistry and Photodegradation of Vanillin.

The photolysis of vanillin produces a short-lived triplet state where its lifetime is controlled by efficient self-quenching (kSQ ~ 2 × 109  m-1  s-1 ) which also generates radicals. Free radical reactions, including vanillin dimer formation, are responsible for the degradation of vanillin and is accompanied by yellowing of the acetonitrile solutions. Laser flash photolysis studies reveal a triplet absorbing at 390 nm, readily quenched by naphthalenes, conjugated dienes and oxygen. Vanillin is also a good singlet oxygen sensitizer as revealed by its characteristic NIR emission at 1270 nm.