Conformations of cyclopentasilane stereoisomers control molecular junction conductance

Haixing Li; Marc H. Garner; Zhichun Shangguan; Qianwen Zheng; Timothy A. Su; Madhav Neupane; Panpan Li; Alexandra Velian; Michael L. Steigerwald; Shengxiong Xiao; Colin Nuckolls; Gemma C. Solomon; Latha Venkataraman

doi:10.1039/C6SC01360K

Conformations of cyclopentasilane stereoisomers control molecular junction conductance†

Haixing Li,‡^a Marc H. Garner,‡^b Zhichun Shangguan,‡^c Qianwen Zheng,^c Timothy A. Su,^d Madhav Neupane,^d Panpan Li,§^c Alexandra Velian,

^d Michael L. Steigerwald,^d Shengxiong Xiao,

*^c Colin Nuckolls,*^cd Gemma C. Solomon*^b and Latha Venkataraman*^ad

Author affiliations

* Corresponding authors

^a Department of Applied Physics and Applied Mathematics, Columbia University, New York 10027, USA
E-mail: lv2117@columbia.edu

^b Nano-Science Center and Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen Ø, Denmark
E-mail: gsolomon@chem.ku.dk

^c The Education Ministry Key Lab of Resource Chemistry, Shanghai Key Laboratory of Rare Earth Functional Materials, Optoelectronic Nano Materials and Devices Institute, Department of Chemistry, Shanghai Normal University, Shanghai 200234, China
E-mail: senksong@msn.com

^d Department of Chemistry, Columbia University, New York 10027, USA
E-mail: cn37@columbia.edu

Abstract

Here we examine the impact of ring conformation on the charge transport characteristics of cyclic pentasilane structures bound to gold electrodes in single molecule junctions. We investigate the conductance properties of alkylated cyclopentasilane cis and trans stereoisomers substituted in the 1,3-position with methylthiomethyl electrode binding groups using both the scanning tunneling microscope-based break junction technique and density functional theory based ab initio calculations. In contrast with the linear ones, these cyclic silanes yield lower conductance values; calculations reveal that the constrained dihedral geometries occurring within the ring are suboptimal for σ-orbital delocalization, and therefore, conductance. Theoretical calculations reproduce the measured conductance trends for both cis and trans isomers and find several distinct conformations that are likely to form stable molecular junctions at room temperature. Due to the weakened σ-conjugation in the molecule, through-space interactions are found to contribute significantly to the conductance. This manuscript details the vast conformational flexibility in cyclopentasilanes and the tremendous impact it has on controlling conductance.

This article is part of the themed collection: ISACS18: Challenges in Organic Materials and Supramolecular Chemistry

Chemical Science

Conformations of cyclopentasilane stereoisomers control molecular junction conductance†

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Conformations of cyclopentasilane stereoisomers control molecular junction conductance

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