Visible Absorption Spectrum of Benzophenone Radical Anion in Dipolar Aprotic Solvents

Abstract

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 (Ph2C•-O-) in the visible region. In 11 dipolar aprotic solvents characterized by ε > 10, in which the Ph2C•-O- anions are not associated with (C2H5)4N+ cations (the radicals were prepared by cathodic reduction of benzophenone in the presence of (C2H5)4N+ClO4- as electrolyte) a correlation equation has the form νmax (in cm-1) = 86.2(AN) - 19.7 · 103[(ε - 1)/(2ε + 1)] + 21.32 · 103. 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 Ph2C•-O- during excitation.