Singlet oxygen sensitisation in supercritical fluids

Supercritical fluids have been the subject of much recent interest as solvents in which to study fundamental photochemical reactions, since they allow, through changes in pressure and temperature, changes in a number of solvent parameters without changing chemical identity. As a result it is possible to control or tune a reaction by adjusting temperature and/or pressure. Ground state molecular oxygen (3Σg-) is a potent quencher of electronically excited states of molecules. Transient absorption of triplet benzophenone (3BP) has been studied as a function of temperature and pressure, to investigate the reactivity of triplet benzophenone toward molecular oxygen, in supercritical carbon dioxide. The spin statistical factors suggests a maximum of 4/9 possible pathways result in quenching for two triplets, proceeding either via energy transfer to molecular oxygen (1/9) or via intersystem crossing to the ground state (3/9). [Continues.]