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Understanding the charge transport properties of redox active metal-organic conjugated wires.


ABSTRACT: Layer-by-layer assembly of the dirhodium complex [Rh2(O2CCH3)4] (Rh2) with linear N,N'-bidentate ligands pyrazine (LS) or 1,2-bis(4-pyridyl)ethene (LL) on a gold substrate has developed two series of redox active molecular wires, (Rh2LS) n @Au and (Rh2LL) n @Au (n = 1-6). By controlling the number of assembling cycles, the molecular wires in the two series vary systematically in length, as characterized by UV-vis spectroscopy, cyclic voltammetry and atomic force microscopy. The current-voltage characteristics recorded by conductive probe atomic force microscopy indicate a mechanistic transition for charge transport from voltage-driven to electrical field-driven in wires with n = 4, irrespective of the nature and length of the wires. Whilst weak length dependence of electrical resistance is observed for both series, (Rh2LL) n @Au wires exhibit smaller distance attenuation factors (?) in both the tunneling (? = 0.044 Å-1) and hopping (? = 0.003 Å-1) regimes, although in (Rh2LS) n @Au the electronic coupling between the adjacent Rh2 centers is stronger. DFT calculations reveal that these wires have a ?-conjugated molecular backbone established through ?(Rh2)-?(L) orbital interactions, and (Rh2LL) n @Au has a smaller energy gap between the filled ?*(Rh2) and the empty ?*(L) orbitals. Thus, for (Rh2LL) n @Au, electron hopping across the bridge is facilitated by the decreased metal to ligand charge transfer gap, while in (Rh2LS) n @Au the hopping pathway is disfavored likely due to the increased Coulomb repulsion. On this basis, we propose that the super-exchange tunneling and the underlying incoherent hopping are the dominant charge transport mechanisms for shorter (n ? 4) and longer (n > 4) wires, respectively, and the Rh2L subunits in mixed-valence states alternately arranged along the wire serve as the hopping sites.

SUBMITTER: Bu D 

PROVIDER: S-EPMC5934749 | biostudies-literature | 2018 Apr

REPOSITORIES: biostudies-literature

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Understanding the charge transport properties of redox active metal-organic conjugated wires.

Bu Donglei D   Xiong Yingqi Y   Tan Ying Ning YN   Meng Miao M   Low Paul J PJ   Kuang Dai-Bin DB   Liu Chun Y CY  

Chemical science 20180219 14


Layer-by-layer assembly of the dirhodium complex [Rh<sub>2</sub>(O<sub>2</sub>CCH<sub>3</sub>)<sub>4</sub>] (Rh<sub>2</sub>) with linear <i>N</i>,<i>N</i>'-bidentate ligands pyrazine (L<sub>S</sub>) or 1,2-bis(4-pyridyl)ethene (L<sub>L</sub>) on a gold substrate has developed two series of redox active molecular wires, (Rh<sub>2</sub>L<sub>S</sub>) <sub><i>n</i></sub> @Au and (Rh<sub>2</sub>L<sub>L</sub>) <sub><i>n</i></sub> @Au (<i>n</i> = 1-6). By controlling the number of assembling cycles, t  ...[more]

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