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Crystal violet (CV + ) and five related triarylmethane dyes quench triplet benzophenone ( 3 K) in acetonitrile at diffusion-controlled rates ( k q ∼ 1 × 10 10 M −1 s −1 ). The interaction with CV + results in bleaching of CV + with a quantum yield, K Φ (−CV + ), dependent on the concentration of CV + with a limiting value of 0.2 at high [CV + . Benzopinacol (K 2 H 2 ) is also formed in this reaction but its yield decreases as [CV + ] increases. In contrast, although both triplet anthracene ( 3 An) and triplet naphthalene ( 3 Nap) are also efficiently quenched by CV + at diffusion-controlled rates, there is only very inefficient fading, An Φ (−CV + ) = 1.1 × 10 −5 . These results are interpreted in terms of a mechanism in which energy transfer to form triplet crystal violet, 3 CV + , is the only major channel in the case of anthracene and naphthalene, i.e. 3 CV + (like 1 CV + ) is unreactive. However, in the case of benzophenone, reduction of 3 K by CV + with a rate constant k h = 1.4 × 10 9 M −1 s −1 to form ketyl radicals (KH . ) can compete (about 14%) with this energy transfer. The ketyl radicals so formed can either reduce CV + to form leuco crystal violet (CVH) or form benzopinacol. |
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