THE ELECTRONIC-STRUCTURE OF HELICENE BISQUINONE ANION RADICALS

Helicene-bisquinones with five, six, seven, and eight rings were studied by cyclic voltammetry, and their anion radicals, prepared electrochemically, were studied by visible, near-IR, and ESR spectroscopy. The large separation between reduction potentials, the well-defined absorptions at very long wavelengths, and hyperfine splittings in the ESR spectra that are independent of temperature all imply that unlike linear analogs, the helical bisquinone anion radicals have delocalized electronic structures. PPP semiempirical calculations correctly account for these experimental observations. They do so, however, only if the assumption is made that the odd electron is not only delocalized between the conjugated rings but also across the gap separating the ends, as in a Mobius array.