ON THE MECHANISM OF QUENCHING OF SINGLET OXYGEN IN SOLUTION

Abstract

Abstract— Bimolecular rate constants for the quenching of singlet oxygen O* 2 ( 1 Δ g ), have been obtained for several transition‐metal complexes and for β‐carotene. Laser photolysis experiments of aerated solutions, in which triplet anthracene is produced and quenched by oxygen, yielding singlet oxygen which then sensitizes absorption due to triplet carotene, firmly establishes diffusion‐controlled energy transfer from singlet oxygen as the quenching mechanism in the case of β‐carotene. The efficient quenching of singlet oxygen by two trans‐planar Schiff‐base Ni(II) complexes, which have low‐lying triplet ligand‐field states, most probably also occurs as a result of electronic energy transfer, since an analogous Pd(II) complex and ferrocene, which both have lowest‐lying triplet states at higher energies than the O* 2 ( 1 Δ g ), state, quench much less effectively.