The Quenching of Singlet Oxygen (1Δg) by Transition Metal Chelates

Various transition metal chelates were found to quench 1O2 in the liquid phase. 1O2 was generated either photochemically, from an ozonide, or with a microwave source and reacted with rubrene or 3-methyl-2-pentene. Rate constants for 1O2 quenching by the chelates were measured in various solvents using the three 1O2 sources, and compared with the constants of previously known 1O2 quenchers. The most efficient chelates quenched 1O2 at close to the diffusion controlled rate, as did β-carotene. Some quenchers of 1O2 in the liquid phase were qualitatively shown to quench in the solid state. The possible 1O2 quenching mechanisms of the chelates are discussed.