REDUCTION OF TRIPHENYL METHANE DYES BY THE DIPHENYL KETYL RADICAL AND HYDRATED ELECTRONS - A TIME-RESOLVED STUDY

The reduction of four triphenyl methane (TPM) dyes (brilliant green (BG(+)), malachite green (MG(+)), crystal violet (CV+) and methyl green (MEG(2+))) 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) x 10(8), (1.5 +/- 0.2) x 10(9), (4.0 +/- 0.5) X 10(8) and (1.0 + 0.15) x 10(10) dm(3) mol(-1) s(-1) respectively and for the reaction with e(aq)(-) are (9.5 +/- 1.0) X 10(9), (9.3 +/- 1.0) X 10(9), (4.0 +/- 0.7) x 10(10) and (3.7 +/- 0.4) X 10(10) dm(3) mol(-1) s(-1) respectively. The transient spectra resulting from the reduction of the dyes were characterized. The time-resolved spectra and pH variation indicate that the dye radical generated from the fake e(aq)(-) reaction is subsequently protonated. The dye radicals decay by a second-order process without giving rise to bleach recovery.