Decay kinetics of photosensitized triplet crystal violet in acetonitrile

Abstract Triplet excited state crystal violet ( 3 CV + ) was produced in acetonitrile via triplet sensitization by anthracene (An) which was excited by Nd:YAG laser at 355 nm. The kinetics of the formation and decay of 3 CV + 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 quenching of triplet anthracene by crystal violet by electron transfer to yield radicals (reaction 3b, 13%) as opposed to energy transfer to yield 3 CV + (reaction 3a, 87%). The 3 CV + so formed returns to the ground state 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 radical formation (6b). The crystal violet radicals formed in both electron-transfer processes ultimately revert to CV + resulting in a very low yield for triplet-sensitized consumption of CV + . The rate constants and branching parameters for the elementary processes in the reaction scheme were determined. The absorbance changes during the bleach and recovery were also monitored at 520, 540, 560, and 605 nm. The absorbance ratios for these wavelengths relative to 590 nm, during the bleach and recovery were the same as for CV + absorption, suggesting that depopulation of 3 CV + results in rapid reversion to normal CV + ground state conformation.