Through-bond conjugated molecules are the major frameworks for traditional molecular wires, while through-space conjugated units are rarely utilized and studied although they have shown unique conducting potential. Herein, we present novel single-molecule wires built on through-space conjugated hexaphenylbenzene. Their conductance, measured by the scanning tunneling microscopy based break-junction technique, increases with the improvement of through-space conjugation and finally reaches a remarkable value (12.28 nS) which greatly exceeds that of conventional through-bond conjugated counterpart (2.45 nS). The multichannel conducting model by integrating through-space and through-bond conjugations could be a promising strategy for the further design of robust single-molecule wires with advanced conductance and stability.

In this Article, the single molecular junctions of thiophene-based molecules are measured by scanning tunneling microscopy break junction (STM-BJ) in ambient air. While the benzo­[1,2-b:4,5-b′]­dithiophene (1) and 2,6-dibromobenzo­[1,2-b:4,5-b′]­dithiophene (2) give out histograms with well-defined peaks corresponding to the molecular junction, thieno­[3,2-b]­thiophene (3) does not show a peak for the molecular junction. The disappearance of peak may contribute to the weak interaction between thiophene and Au. DFT calculation results demonstrate the weak interaction for 3 contacting Au as compared to 1 and 2. Interestingly, the step probability for molecular junction follows the order of binding interaction between thiophene and Au showing 1 > 2 > 3. The current results reveal the influence of molecular structure on contact interaction between anchoring group and electrode, which can help to understand the electron transport of the single molecular junction.

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We have measured the alkane and benzene-based molecules with aldehyde and carboxylic acid as anchoring groups by using the electrochemical jump-to-contact scanning tunneling microscopy break junction (ECSTM-BJ) approach. The results show that molecule with benzene backbone has better peak shape and intensity than those with alkane backbone. Typically, high junction formation probability for same anchoring group (aldehyde and carboxylic acid) with benzene backbone is found, which contributes to the stronger attractive interaction between Cu and molecules with benzene backbone. The present work shows the import role of backbone in junction, which can guide the design molecule to form effective junction for studying molecular electronics.

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