Dual Modulation of Single Molecule Conductance via Tuning Side Chains and Electric Field with Conjugated Molecules Entailing Intramolecular O•••S Interactions

Abstract

Herein, single‐molecule conductance studies of TBT1‐TBT6 which entails 1,4‐dithienylbenzene as the backbone and SMe groups as the anchoring units, with the scanning tunneling microscope break junction (STM‐BJ) technique, are reported. The molecular conductance of TBT1 with intramolecular O•••S noncovalent interactions is enhanced by about one order of magnitude in comparison to their analogue TBT2 (which contains alkyl instead of alkoxy chains). By replacing the methoxy groups in TBT1 with extending alkoxy chains in TBT3, TBT4, and TBT5, the molecular backbones become twisted and as a consequence the single‐molecule conductance decreases gradually, showing that the intramolecular O•••S noncovalent interaction is influenced by the structural features of alkoxy chains. More importantly, the single‐molecule conductance of TBT3, TBT4, and TBT5 can be boosted by increasing the electric field applied to the molecular junctions. Remarkably, the conductance of TBT3, TBT4, and TBT5 can be reversibly modulated due to the conformational changes between twisted and planar ones by varying the electric field. These results demonstrate that molecules with intramolecular O•••S noncovalent interactions have the potential for in situ control of the electrical properties of molecular‐scale devices.

A new anchoring group to fabricate single-molecule junctions: diphenyl sulfide

“…Meanwhile, these molecules were optimized with DFT calculations, and the S–S′ and S–S distances are summarized in Table 1. After adding the snap-back distance (0.5 nm) 35 of the Au electrode to Δ d , we found the results (Δ d + 0.5) approximate the S–S′ lengths of the six molecules, and are about half of their S–S distances. This further indicates that the observed conductance states are produced by the backbones between the S and S′ atoms.…”

Lest We Forget–The Importance of Heteroatom Interactions in Heterocyclic Conjugated Systems, from Synthetic Metals to Organic Semiconductors

“…The effect of S•••O non-covalent interactions on the conductivity of single molecules with methylthio anchor groups and a di(thiophen-2-yl)benzene conjugated backbone was studied using compounds 22 and 23, systems with S•••O conformational locks, as well an analogous molecule (24) without intramolecular non-covalent interactions (Figure 8). [27] The crystal structure of 22 revealed a S•••O distance of 2.707 Å and a dihedral angle between thiophene and benzene rings of only 1.7°. Compound 23, which had bulky alkoxy substituents, exhibited a similar S•••O interaction distance of 2.742 Å but had a higher dihedral angle of 20.1°.…”

Recent progress in tuning charge transport in single-molecule junctions by substituents

“…6c). 78 The OÁ Á ÁS interaction can effectively overcome the steric hindrance-caused conformational twist and restrain the two adjacent rings to be planar. 77 The single-molecule conductance of the molecules with OÁ Á ÁS non-covalent interaction is enhanced by about one order of magnitude compared with the molecules in which the interaction was absent.…”