title: Engineering a remarkably low HOMO-LUMO gap by covalent linkage of a strong pi-donor and a pi-acceptor--tetrathiafulvalene-sigma-polynitrofluorene diads: their amphoteric redox behavior, electron transfer and spectroscopic properties.
abstract: Novel R3TTF-sigma-A compounds 14, 16 and 19 (R3TTF = trial-kyletrathiafulvalene, sigma = saturated spacer, A = polynitrofluoren-9-dicyano-methylene acceptor) incorporating very strong donor and acceptor moieties have been synthesized by condensation of the corresponding R3TTF-sigma-fluoren-9-one diads with malononitrile. Reversible five-step amphoteric redox behavior has been observed with an extremely low HOMO-LUMO gap (approximately 0.3 eV). For compound 14 a strong EPR signal is observed in the solid state, ascribed to intermolecular complexation: a less intense signal is seen in solution, corresponding to ca. 2% of the molecules existing in a radical form at room temperature. Intramolecular charge transfer in diads 14 and 16 is manifested in strong absorption bands in the near-IR region of their electronic spectra. Spectroelectrochemical data reveal marked electrochromic behavior in the visible and near-IR region of both compounds. The first X-ray crystal structure of a fluorene radical-anion salt is reported, namely the copper salt of 2,4,5,7-tetranitro-9- dicyanomethylenefluorene (1:1 stoichiometry).
authors.affiliation: Department of Chemistry, University of Durham, Durham DH1 3LE, UK.
authors.forename: Dmitrii F
authors.initials: DF
authors.lastname: Perepichka
authors.forename: Martin R
authors.initials: MR
authors.lastname: Bryce
authors.forename: Andrei S
authors.initials: AS
authors.lastname: Batsanov
authors.forename: Eric J L
authors.initials: EJ
authors.lastname: McInnes
authors.forename: Jing P
authors.initials: JP
authors.lastname: Zhao
authors.forename: Robert D
authors.initials: RD
authors.lastname: Farley