Ultra-highly conductive optoelectronic modulated single-molecule nickel bis(dithiolene) junctions with strong molecule-electrode coupling

Strong molecule-electrode coupling originating from orbit hybridization between gold and the delocalized molecular wires in single-molecule junctions facilitates facile transport towards smart molecular devices. In this paper, we report ultra-highly conductive single-molecule circuits based on highly delocalized nickel bis(dithiolene) (NiS₄) molecular junctions using scanning tunneling microscope break junction technique. Single-molecule charge transport measurement of both NiS₄ reveals they exhibits high conductance of 10^−1.49 G₀ and 10^−1.51 G₀, respectively. Moreover, under intervention of high bias voltage the molecular conductance could be further improved to approximately 10^−1.00 G₀, the highest value reported to date with similar molecular lengths. Theoretical calculations suggest that the strong hybridization of the π-channels and the gold electrodes in both junctions exists and it further extends from molecule-electrode interfaces to metal electrodes as visualized by the isosurface plots of the transmitting eigenstate, which lead to not only a distinct energy shift of the dominated LUMO peaks toward Fermi level, but also broad peaks in the LUMO resonance in the transmission functions. In addition, the both molecular junctions show remarkable photoconductance of approximately 10^−1.00 G₀ under resonant light excitation, due to possible exciton binding in these junctions. Interestingly, the conductance switching of both molecular junctions under optoelectronic modulation is highly reversible, forming a multi-stimulus responsive molecular switch. This work not only provides a building block for fabricating highly conducting molecular wires with strong molecule-electrode coupling, but also lays a foundation for designing optoelectronic modulated functional molecule-scale devices.