TRANSIENT PHOTOCHEMISTRY OF NEUTRAL RED

Abstract

Abstract— Flash photolysis of neutral red between pH 1.3 and pH 11 yields the triplet species 3 DH 2 +2 3 DH + and 3 D. Both 3 DH 2 +2 and 3 D exhibit first order decay with rate constants of 1.6 ± 0.3 × 10 4 s ‐1 but 3 DH + decays within the lifetime of the flash. Over the entire pH range, ascorbic acid quenches the triplet, forming the semireduced radicals DH 3 +2 DH 2 + and DH, all of which exhibit second order decay with k = 1.8 ± 0.4 ± 10 8 M ‐1 s ‐1 most probably by recombination with semioxidized ascorbic acid. The dependence of the rate of decay of radical neutral red on the identity of reversible reductants supports the back‐electron transfer mechanism, as does digital simulation of complex radical disproportionation schemes. In contrast to the efficient reduction of triplet neutral red by ascorbic acid, its reduction by EDTA is quite inefficient.