ELECTRONIC-STRUCTURE AND NEAR-INFRARED SPECTRA OF DIQUINONE ANION RADICALS

The preparation of several substituted anthracene diquinones (1,4,5,8-anthracenetetrones), 1,4,6,11-naphthacenetetrone, and 5,7,12,14-pentacenetetrone is reported. These compounds, which have two quinones separated by one aromatic ring, were reduced electrochemically in aprotic solvents containing Bu4N·BF4 to produce the anion radicals (semiquinones) and dianions. Eo values were estimated by cyclic voltammetry. The semiquinones were characterized by ESR and were stable in the absence of air. The semiquinones have intense, sharp bands in the near-infrared (1-1.5 μm). These bands are not found for monoquinone anion radicals. Solvent, counterion, and substituent effects are described. Ab initio theoretical calculations were performed on neutral diquinones, semiquinones, and semiquinone excited states to reveal the origin of the spectra as π⋆-π⋆ excitations from delocalized anions. Infrared spectra are reported for 1,4,5,8-anthracenetetraone and its anion radical which demonstrate that the semiquinone does not have a localized charge on the IR time scale. Dianions were diamagnetic and gave electronic excitation bands near 880 nm. © 1990, American Chemical Society. All rights reserved.