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Exceptional Single-Molecule Transport Properties of Ladder-Type Heteroacene Molecular Wires

Author(s):

Zhengxu Cai, Wai-Yip Lo, Tianyue Zheng, Lianwei Li, Na Zhang, Yubing Hu, Luping Yu

Journal:

Journal of the American Chemical Society

Year:

2016

Volume:

138

Pages

10630-10635

DOI:

10.1021/jacs.6b05983

Abstract:

A series of ladder-type fused heteroacenes consisting of thiophenes and benzothiophenes were synthesized and functionalized with thiol groups for single-molecule electrical measurements via a scanning tunneling microscopy break-junction method. It was found
that this molecular wire system possesses exceptional charge transport properties with weak length dependence. The tunneling decay constant β was estimated to be 0.088 and 0.047 Å−1 under 0.1 and 0.5 bias, respectively, which is one of the lowest β values among other non-metal-containing molecular wires, indicating that a planar ladder structure favors charge transport. Transition voltage spectroscopy showed that the energy barrier decreases as the length of the molecule increases. The general trend of the energy offsets derived from the transition voltage via the Newns−Anderson model agrees well with that of the Fermi/HOMO energy level difference. Nonequilibrium Green’s function/density functional theory was used to further investigate the transport process in these molecular wires.

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