Photochemistry of "Super" Photoacids. 2. Excited-State Proton Transfer in Methanol/Water Mixtures

Kyril M. Solntsev, Dan Huppert, Noam Agmon, Laren M. Tolbert

Research output: Contribution to journalArticlepeer-review

Abstract

Excited-state proton transfer to solvent (PTTS) of 5-cyano-2-naphthol was investigated in methanol/water mixtures. We have found that the time-resolved fluorescence data fit the solution of the Debye-Smoluchowski equation for the reversible geminate recombination of ions over the whole range of methanol/water concentration ratios. The rate constants of the elementary protolytic photochemical processes and their isotope effects were determined by a simultaneous analysis of the time-resolved fluorescence of the photoacid and its conjugated anion. The competition between adiabatic protonation and quenching of the excited naphtholate anion by the geminate proton was observed to diminish sharply near pure methanol. The dissociation rate coefficient near pure methanol depends on a power of the water concentration, which appears to decrease from 2 (for "ordinary" photoacids) to below 1 for "super" photoacids.

Original languageEnglish
Pages (from-to)4658-4669
Number of pages12
JournalJournal of Physical Chemistry A
Volume104
Issue number19
DOIs
StatePublished - 18 May 2000

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