Photoelectron spectroscopy of microsolvated benzophenone radical anions to reveal the origin of solvatochromic shifts in alcoholic media

The 355 nm photoelectron spectra of bare and methanol-solvated radical anions of benzophenone were measured. Sequential shifts of the vertical detachment energy represent a similarity in shape to those of the photoabsorption spectrum reported previously, exhibiting near convergence for solvation with two methanol molecules. An analysis of the solvation energetics shows that the solvatochromic shifts in alcoholic media are essentially caused by a change of long-range interactions involving the excess charge delocalized over the anion, instead of a former explanation based on local hydrogen-bonding of solvents with the singly occupied molecular orbital in the ground state.