Solvatochromic Shift of Aromatic Ketyl Anions due to Hydrogen Bonding

Article abstract of DOI:10.1246/bcsj.64.2695

The electronic spectra of fluorenone radical anions generated by γ-irradiation at 77 K in glassy matrices of ethanol and ethanol-2-methyltetrahydrofuran mixtures have been measured for elucidating the mechanism of the spectral change due to solvation of the radical anions by alcohols.Three kinds of the radical anions are generated in the mixed solvent: the radical anions without hydrogen bond (ε=1.05*10⁴dm³mol^-1cm^-1 at λ_max=568 nm), with one ethanol molecule (ε=0.67*10⁴dm³mol^-1cm^-1 at λ=529 nm) and two ethanol molecules (ε=0.37*10⁴dm³mol^-1cm^-1 at λ=448 nm) hydrogen-bonded through the ? electron on the carbonyl oxygen.The spectral shift and the decrease of the molar extinction coefficient of aromatic ketyl radical anions are explained as due to the stabilization of a carbonyl antibonding ? orbital by hydrogen bonding.