Simultaneous Determination of the Chemical (kr) and the Physical (kq) Quenching Rate Constants of Singlet Oxygen in Aqueous Solution by the Chemiluminescence‐quenching Method†

This work reports a novel and visual method for the simultaneous determination of the chemical (kr ) and the physical (kq ) quenching rate constants of singlet oxygen (1 O2 ,1 ∆g ) in aqueous media. It is based on the disruption, by a water-soluble substrate S, of the 1 O2 chemiluminescence (CL) generated by the H2 O2 /Na2 MoO4 catalytic system. A mathematical analysis of the CL signal at 1270 nm vs time provides separately the overall (kr + kq ) and the chemical (kr ) quenching rate constants. In ordinary water (H2 O), 1 O2 lifetime is short and the CL intensity is weak allowing solely the investigation of very reactive substrates for which (kr + kq ) > 3 × 106 m-1 s-1 while, in D2 O, 1 O2 lifetime is significantly longer lifetime and the CL signal is much stronger allowing the study of poorly reactive substrates for which (kr + kq ) > 4 × 105 m-1 s-1 . The method has been successfully tested on a series of anionic and nonionic water-soluble naphthalene derivatives commonly used as bio-compatible 1 O2 carriers. The obtained kr and kq values are in good agreement with the values determined by conventional techniques, namely, flash photolysis and competitive kinetics with a reference quencher.