title: Electronic communication in linear oligo(azobenzene) radical anions.
abstract: The radical anions of five bis(azobenzene) and one tris(azobenzene) compounds were studied by optical and electron paramagnetic resonance (EPR) spectroscopies in polar aprotic solvents. The radicals with planar or almost-planar bridges are charge-delocalized mixed-valence species. Localization of charge occurs only on radicals with highly twisted biphenyl bridges. The electronic coupling between the azobenzene charge-bearing units, calculated as half the energy of the intervalence band for the charge-delocalized and by the Hush equation for the charge-localized radicals, decreases with the distance and torsion angle between azobenzene units. These radicals have smaller electronic couplings between charge-bearing units than other mixed-valence organic radicals with similar bridges. However, the application of a three-stage model to the tris(azobenzene) radical anion intervalence band yields an electronic coupling between consecutive azobenzenes that is higher than in any of the bis(azobenzene) radicals studied.
authors.affiliation: Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa , Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
authors.forename: Álvaro
authors.initials: Á
authors.lastname: Moneo
authors.forename: Gonçalo C
authors.initials: GC
authors.lastname: Justino
authors.forename: M Fernanda N N
authors.initials: MF
authors.lastname: Carvalho
authors.forename: M Conceição
authors.initials: MC
authors.lastname: Oliveira
authors.forename: Alexandra M M
authors.initials: AM
authors.lastname: Antunes
authors.forename: David
authors.initials: D
authors.lastname: Bléger
authors.forename: Stefan
authors.initials: S
authors.lastname: Hecht
authors.forename: João P
authors.initials: JP
authors.lastname: Telo