TRIPLET-SENSITIZED PHOTOBLEACHING OF CRYSTAL VIOLET

Crystal violet (CV+) and five related triarylmethane dyes quench tripl er benzophenone (K-3) in acetonitrile at diffusion-controlled rates (k (q) approximate to 1 x 10(10) M(-1) s(-1)). The interaction with CV+ r esults in bleaching of CV+ with a quantum yield, (K) Phi(-CV+), depend ent on the concentration of CV+ with a limiting value of 0.2 at high [ CV+]. Benzopinacol (K2H2) is also formed in this reaction but its yiel d decreases as [CV+] increases. In contrast, although both triplet ant hracene ((3)An) and triplet naphthalene ((3)Nap) are also efficiently quenched by CV+ at diffusion-controlled rates, there is only very inef ficient fading, (An)Phi(-CV+) = 1.1 x 10(-5). These results are interp reted in terms of a mechanism in which energy transfer to form tripler crystal violet, (CV+)-C-3, is the only major channel in the case of a nthracene and naphthalene, i.e. (CV+)-C-3 (like (CV+)-C-1) is unreacti ve. However, in the case of benzophenone, reduction of K-3 by CV+ with a rate constant k(h) = 1.4 x 10(9) M(-1) s(-1) to form ketyl radicals (KH.) can compete (about 14%) with this energy transfer. The ketyl ra dicals so formed can either reduce CV+ to form leuco crystal violet (C VH) or form benzopinacol.