Visible Absorption Spectrum of Benzophenone Radical Anion in Dipolar Aprotic Solvents

Two-parameter regression including the acceptor number (AN) and permittivity (ε) of the solvent explains to some extent the solvatochromic shift of the absorption band of benzophenone radical anion (Ph 2 C • -O - ) in the visible region. In 11 dipolar aprotic solvents characterized by ε > 10, in which the Ph 2 C • -O - anions are not associated with (C 2 H 5 ) 4 N + cations (the radicals were prepared by cathodic reduction of benzophenone in the presence of (C 2 H 5 ) 4 N + ClO 4 - as electrolyte) a correlation equation has the form ν max (in cm -1 ) = 86.2(AN) - 19.7 · 10 3 [(ε - 1)/(2ε + 1)] + 21.32 · 10 3 . It reflects the relative stabilization of the ground state in a medium with a high acceptor number and an increase in the dipole moment of Ph 2 C • -O - during excitation.