Photochemistry of 5-phenyltricyclo[5.2.1.02,6]deca-4,8-dien-3-one: upper singlet excited state involved in intramolecular [2 + 2] photocycloaddition and long-lived triplet excited state in photodimerisation

Abstract

Upon π,π* excitation, 5-phenyltricyclo[5.2.1.0^2,6]deca-4,8-dien-3-one predominantly undergoes intramolecular [2 + 2] photocycloaddition probably via the higher singlet excited state (S₂), while, upon n,π* excitation, it undergoes predominantly photodimerisation via a relatively long-lived triplet excited state.