Photochemical generation of singlet oxygen on non-transition-metal oxide surfaces

Irradiation of the non-transition-metal oxide powders silica gel, aluminium oxide and magnesium oxide in the presence of oxygen results in the formation of singlet oxygen (1O2). Two specific chemical traps were used to detect 1O2: 1,2-dimethylcyclohexene and geminally deuterated [2H6]-2,3-dimethylbut-2-ene. Both compounds gave product distributions characteristic of singlet-oxygen reactions when irradiated on the metal oxide surfaces. These results support previous suggestions that singlet oxygen is formed through an energy-transfer process involving oxygen and excitons on the metal oxide surface. Under the same reaction conditions TiO2 showed no production of 1O2.