Diazonium salts in photochemistry. I. Quenching of triplet photosensitizers

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Abstract
Aromatic diazonium tetrafluoroborates have been shown to be excellent triplet quenchers. Typical rate constants obtained using laser flash photolysis are in the 1–10 × 109 M−1 s−1 range in acetonitrile at 300 K. With most sensitizers the interaction leads to the dediazoniation reaction, via either energy transfer or electron transfer mechanisms. In the case of anthracene, where the rate constant for benzenediazonium tetrafluoroborate is (5.4 ± 0.3) × 109 M−1 s−1, the reaction involves the transfer of an electron, leading to the formation of anthracene radical-cation, which has been characterized by absorption spectroscopy. High energy sensitizers, such as benzophenone, are believed to lead to aryl cations and nitrogen; the process may involve some degree of charge transfer, since it is somewhat faster when electron donating substituents are present in the diazonium salt.

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