Decay kinetics of photosensitized triplet crystal violet in acetonitrile

Triplet excited state crystal violet ((CV+)-C-3) was produced in acetonitri le via triplet sensitization by anthracene (An) which was excited by Nd:YAG laser at 355 nm. The kinetics of the formation and decay of (CV+)-C-3 were mostly studied by monitoring the bleach and recovery of CV+ at 590 nm (the absorbance maximum). This allows the determination of the percentage of qu enching of triplet anthracene by crystal violet by electron transfer to yie ld radicals (reaction 3b, 13%) as opposed to energy transfer to yield (CV+) -C-3 (reaction 3a, 87%). The (CV+)-C-3 so formed returns to the ground stat e by a first-order process (4) and also by reaction with ground state CV+ ( 6). There are two channels for the latter reaction. One is direct reversion to the ground state (6a), the other is electron transfer resulting in radi cal formation (6b). The crystal violet radicals formed in both electron-transfer processes ulti mately revert to CV+ resulting in a very low yield for triplet-sensitized c onsumption of CV+. The rate constants and branching parameters for the elem entary processes in the reaction scheme were determined. The absorbance cha nges during the bleach and recovery were also monitored at 520, 540, 560, a nd 605 nm. The absorbance ratios for these wavelengths relative to 590 nm, during the bleach and recovery were the same as for CV+ absorption, suggest ing that depopulation of (CV+)-C-3 results in rapid reversion to normal CV ground state conformation. (C) 2001 Elsevier Science B.V. All rights reser ved.