Effects of long-chain alkyl substituents on the protolytic reactions of naphthols

An efficient deactivation process competing with the excited-state proton transfer (ESPT) was observed both for 1N and 2O1N. This needs more complicated kinetic analysis, yet provided a deeper insight into mechanisms of the excited-state proton-transfer reactions. A simple kinetic scheme including transient formation of excited hydrogen-bonded complex and geminate ion-pair and fast deactivation of both transients provided a good description of the protolytic photodissociation for the compounds studied. The rate constants for proton transfer and induced deactivation were determined for photodissociation of excited 1N and 2O1N in aqueous acetonitrile and their reactions with acetate anion in absolute ethanol. A remarkable decrease of ESPT rate constant and a substantial increase of the radiationless decay rate constant was observed in aqueous acetonitrile as compared to water. The origin of dissimilar solvent effects on these rate constants was discussed.