Quenching of Benzene Fluorescence by Oxygen

Abstract

Molecular oxygen has been found to quench benzene fluorescence without noticeably decreasing the concentration of the benzene triplet ( 3 B 1u ) although the fluorescing species, the excited singlet 1 B 2u , is the precursor of the triplet. The most obvious explanation of this apparent anomaly is that the 1 B 2u state is converted to the triplet 3 B 1u when it is quenched by O2, perhaps with simultaneous conversion of O2 to the first excited singlet ( 1 Δ g ) . The estimated values of the quenching rate constants of benzene singlet ( 1 B 2u ) and benzene triplet ( 3 B 1u ) by oxygen are, respectively, k 2d = 2.1 × 10 −10 cc / molecule · sec and k 3c = 2.1 × 10 −11 cc / molecule · sec .