Simultaneous Determination of the Chemical (k ) and the Physical (k ) 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 (k ) and the physical (k ) quenching rate constants of singlet oxygen ( O , ∆ ) in aqueous media. It is based on the disruption, by a water-soluble substrate S, of the O chemiluminescence (CL) generated by the H O /Na MoO catalytic system. A mathematical analysis of the CL signal at 1270 nm vs time provides separately the overall (k  + k ) and the chemical (k ) quenching rate constants. In ordinary water (H O), O lifetime is short and the CL intensity is weak allowing solely the investigation of very reactive substrates for which (k  + k ) > 3 × 10  m  s while, in D O, O lifetime is significantly longer lifetime and the CL signal is much stronger allowing the study of poorly reactive substrates for which (k  + k ) > 4 × 10  m  s . The method has been successfully tested on a series of anionic and nonionic water-soluble naphthalene derivatives commonly used as bio-compatible O carriers. The obtained k and k values are in good agreement with the values determined by conventional techniques, namely, flash photolysis and competitive kinetics with a reference quencher.