Quantum yield of singlet dioxygen and elucidation of the quenching mechanism for the reaction between the doublet excited states of tris(bipyridine)chromium(III) and triplet dioxygen

The formation of singlet dioxygen (1O2) in the reaction between the doublet excited states of tris(bipyridine)chromium(III) and triplet dioxygen in deuterium oxide was detected using near-infrared luminescence corresponding to singlet dioxygen decay. In addition, luminescence intensity measurements were used to determine the quantum yield of singlet dioxygen produced. A value of 0.86 ± 0.08 was obtained for the yield of 1O2. Based on these quantum yield measurements, it is proposed that the major quenching mode is energy transfer quenching. However, considering that the 1O2 yield is less than unity and electron transfer quenching is not a viable pathway, it is proposed that, in addition to the energy transfer quenching, physical quenching involving spin-catalyzed deactivation of Cr(bpy)33+ may also be operative as a minor quenching pathway. Key words: Cr(bpy)33+, singlet dioxygen, quenching, quantum yield.