Fine Tuning the Performance of Multiorbital Radical Conductors by Substituent Effects

Mailman, Aaron, Wong, Joanne WL, Winter, Stephen M, Claridge, Robert CM, Robertson, Craig M ORCID: 0000-0002-4789-7607, Assoud, Abdeljalil, Yong, Wenjun, Steven, Eden, Dube, Paul A, Tse, John S
et al (show 3 more authors) (2017) Fine Tuning the Performance of Multiorbital Radical Conductors by Substituent Effects. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 139 (4). pp. 1625-1635.

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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 U<sub>eff</sub>, the effective Coulombic barrier to charge transfer. The effect is echoed, at the molecular level, in the observed trend in E<sub>cell</sub>, the electrochemical cell potential for 2 with R = F, H and NO<sub>2</sub>. The crystal structures of the MeCN and EtCN solvates of 2 with R = NO<sub>2</sub> have 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 χ<sub>TIP</sub> = 6 × 10<sup>-4</sup> emu mol<sup>-1</sup>, but its charge transport behavior, with σ<sub>RT</sub> near 0.04 S cm<sup>-1</sup> and E<sub>act</sub> = 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.

Item Type: Article
Depositing User: Symplectic Admin
Date Deposited: 07 May 2019 08:57
Last Modified: 19 Jan 2023 00:50
DOI: 10.1021/jacs.6b11779
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