Javier Lopez

The radical ions of hexacene

Abstract The radical anion and the radical cation of hexacene have been characterized by ESR spectroscopy. The electronic absorption spectrum of the former has been recorded and analyzed. Based on a comparison with photoelectron spectroscopic data, the lowest excited state of the hexacene (and pentacene) radical ions is identified as a non-Koopmans state.

The radical anion of [24](1,2,4,5)cyclophane

The radical anion of [24](1,2,4,5)cyclophane (I) has been investigated by e.s.r. and e.n.d.o.r. spectroscopy under a variety of conditions. In dimethylformamide (counterion Et4N+) and in 1,2-dimethoxyethane–hexamethylphosphoric triamide (3 : 1)(counterion K+) a ‘free’ or loosely associated radical anion (If–˙) is formed (effective symmetry D2h), whereas in tetrahydrofuran and 2-methyltetrahydrofuran (counterion K+ or Cs+) a tightly ion paired species (Ip–˙) is present (symmetry C2v; aKca. 0.1 or aCsca. 0.6–0.8 mT). In 1,2-dimethoxyethane (counterion K+), at low temperatures, (If–˙) and (Ip–˙) give rise concurrently to distinct e.s.r. and e.n.d.o.r. spectra; the inter-conversion (If˙+)+ K+⇌(Ip˙–)K+ must thus be slow on the hyperfine time-scale. The concentration ratio [(Ip–˙)]/[(If–˙)] in 1,2-dimethoxyethane is ca. 5 at 178 K and increases upon raising the temperature.