Probing the dynamics of solvation and structure of the oh- ion in aqueous solution from picosecond transient absorption measurements

Abstract

The reaction of intracomplex proton transfer (44BPY-' HO-H) → 44BPYH' + OH- that follows the photoreduction of 4,4'-bipyridine (44BPY) into its anion radical 44BPY- in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) is investigated in acetonitrile-water mixtures by using picosecond transient absorption. The dependence of the appearance kinetics of the 44BPYH' radical on the water content reveals a highly diffusional proton transfer process that is controlled by the dynamics of solvation of the released hydroxide ion. The results are interpreted on the basis of a two-step mechanism where an intermediate lvation complex (44BPYH')OH-(H2O)3 is formed first before evolving toward a final four-water hydration structure OH-(H2O)4. © 2010 by the authors.