Proton transfer to solvent from photoacids has been a subject of intensive research over the past decades. Despite this wealth of information, the mechanism of the proton dissociation still remains unclear. Our contribution to this area involves kinetic studies on photodissociation of strong cationic photoacids by means of time-resolved fluorescence and femtosecond transient absorption. Our data are consistent with a mechanism where the first dissociation step is a reversible process, even for the strongest photoacid 1-methyl-6-hydroxyquinolinium (MQ), whose dissociation rate is controlled by solvation. The proton-transfer contact pair formed in the first step separates in a diffusion-controlled process for MQ, but its dissociation is somewhat slower for the moderately strong photoacid 2-(1'-hydroxy-2'-naphthyl)benzimidazolium. In this communication, we will show the results of photodissociation studies of new photoacids of the hydroxyphenyl- and hydroxypyridylbenzimidazolium families in alcohols and water. The results support the proposed model and allow a deeper insight into the nature of the proton-transfer contact pair and the elementary steps of the proton transfer to solvent.We thank the Spanish Government and EU ERDF (Grants CTQ2010-17835 and CTQ2010-17026) and the Xunta de Galicia (Grants CN 2012/314, EM2012/091, and GPC2013/052) for financial support of our work.

Elementary steps in proton transfer to solvent

248th National Meeting (2014)

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