title: Fine Tuning the Performance of Multiorbital Radical Conductors by Substituent Effects.
abstract: A critical feature of the electronic structure of oxobenzene-bridged bisdithiazolyl radicals 2 is the presence of a low-lying LUMO which, in the solid state, improves charge transport by providing additional degrees of freedom for electron transfer. The magnitude of this multiorbital effect can be fine-tuned by variations in the π-electron releasing/accepting nature of the basal ligand. Here we demonstrate that incorporation of a nitro group significantly stabilizes the LUMO, and hence lowers Ueff, the effective Coulombic barrier to charge transfer. The effect is echoed, at the molecular level, in the observed trend in Ecell, the electrochemical cell potential for 2 with R = F, H and NO2. The crystal structures of the MeCN and EtCN solvates of 2 with R = NO2have been determined. In the EtCN solvate the radicals are dimerized, but in the MeCN solvate the radicals form superimposed and evenly spaced π-stacked arrays. This highly 1D material displays Pauli-like temperature independent paramagnetic behavior, with χTIP= 6 × 10-4emu mol-1, but its charge transport behavior, with σRTnear 0.04 S cm-1and Eact= 0.05 eV, is more consistent with a Mott insulating ground state. High pressure crystallographic measurements confirm uniform compression of the π-stacked architecture with no phase change apparent up to 8 GPa. High pressure conductivity measurements indicate that the charge gap between the Mott insulator and metallic states can be closed near 6 GPa. These results are discussed in the light of DFT band structure calculations.
authors.affiliation: Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Aaron
authors.initials: A
authors.lastname: Mailman
authors.affiliation: Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Joanne W L
authors.initials: JW
authors.lastname: Wong
authors.affiliation: Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Winter
authors.affiliation: Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Robert C M
authors.initials: RC
authors.lastname: Claridge
authors.affiliation: Department of Chemistry, University of Liverpool , Liverpool L69 7ZD, United Kingdom.
authors.forename: Craig M
authors.initials: CM
authors.lastname: Robertson
authors.affiliation: Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Abdeljalil
authors.initials: A
authors.lastname: Assoud
authors.affiliation: Department of Earth Sciences, University of Western Ontario , London, Ontario N6A 5B7, Canada.
authors.forename: Wenjun
authors.initials: W
authors.lastname: Yong
authors.affiliation: Department of Physics, Florida State University , Tallahassee, Florida 32310, United States.
authors.forename: Eden
authors.initials: E
authors.lastname: Steven
authors.affiliation: Brockhouse Institute for Materials Research, McMaster University , Hamilton, Ontario L8S 4M1, Canada.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Dube
authors.affiliation: Department of Physics, University of Saskatchewan , Saskatoon, Saskatchewan S7N 5E2, Canada.
authors.forename: John S
authors.initials: JS
authors.lastname: Tse
authors.affiliation: Department of Physics, University of Ottawa , Ottawa, Ontario K1N 6N5, Canada.
authors.forename: Serge
authors.initials: S
authors.lastname: Desgreniers
authors.affiliation: Department of Earth Sciences, University of Western Ontario , London, Ontario N6A 5B7, Canada.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Secco
authors.affiliation: Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Richard T
authors.identifier: 0000-0002-7185-2580
authors.initials: RT
authors.lastname: Oakley