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 (e_aq^-) 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 e_aq^- 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 e_aq^-1 reaction is subsequently protonated. The dye radicals decay by a second-order process without giving rise to bleach recovery.