Reduction of triphenyl methane dyes by the diphenyl ketyl radical and hydrated electrons: a time-resolved study

Abstract

The reduction of four triphenyl methane (TPM) dyes (brilliant green (BG+), malachite green (MG+), crystal violet (CV+) and methyl green (MEG2+)) by diphenyl ketyl radicals (BPH.) and hydrated electrons (eaq−) was studied by pulse radiolytic kinetic spectrophotometry. The rate constants for the reaction of BPH. with the cationic dyes are (8.0±1.0) × 108, (1.5±0.2) × 109, (4.0±0.5) × 108 and (1.0±0.15) × 1010 dm3mol−1s−1 respectively and for the reaction with eaq− are (9.5±1.0) × 109, (9.3±1.0) × 109, (4.0±0.7) × 1010 and (3.7±0.4) × 1010 dm3 mol−1s−1 respectively. The transient spectra resulting form the reduction of the dyes were characterized. The time-resolved spectra and pH variation indicate that the dye radical generated from the eaq- reaction is subsequently protonated. The dye radicals decay by a second-order process without giving rise to bleach recovery.