Single‐Molecule Conductance of π‐Conjugated Rotaxane: New Method for Measuring Stipulated Electric Conductance of π‐Conjugated Molecular Wire Using STM Break Junction

Abstract

An electronic conductance with small fluctuations, which is stipulated in single-molecule junctions, is necessary for the precise control of single-molecule devices. However, the suppression of conductance fluctuations in conventional molecular junctions is intrinsically difficult because the fluctuations are related to the contact fluctuations and molecular motion. In the present study involving experimental and theoretical investigations, it is found that covering a single π-conjugated wire with an α-cyclodextrin molecule is a promising technique for suppressing conductance fluctuations. The conductance histogram of the covered molecular junction measured with the scanning tunneling microscope break-junction technique shows that the conductance peak for the covered junction is sharper than that of the uncovered junction. The covering technique thus has two prominent effects: the suppression of intramolecular motion, and the elimination of intermolecular interactions. Theoretical calculations of electronic conductance clearly support these experimental observations.

Design principle for increasing charge mobility of π-conjugated polymers using regularly localized molecular orbitals

“…Because the original IMWs include CD molecules, which are not favourable for calculations, we propose an effective IMW (e-IMW) model based on the theoretical finding that the rotation barrier of a benzene in the CD-covered wire at room temperature (RT) is almost equal to that in the uncovered wire at 60 K30 (see Supplementary Note 3). That is, we can estimate the wire dynamics of IMWs at RT from those of an uncovered wire (e-IMW) at 60 K. This fact in turn corresponds to the reduced structural fluctuation/deformation of IMWs, the second characteristic of IMWs.…”

Insulated molecular wires: inhibiting orthogonal contacts in metal complex based molecular junctions

“…In each of these cases, the conceptual design principle involves shielding the π-conjugated backbone of the molecule from adventitious contact within a junction. 90 The motivation for the present study was twofold: (i) to explore the electrical properties and behavior of new trans-bis (alkynyl) platinum complexes within molecular junctions, and (ii) to address issues concerning the design of insulated molecular wires. We demonstrate that when contacted through the trimethylsilylethynyl group installed at the remote ends of the molecular backbone, the trans-bis(alkynyl) platinum complexes examined here display single molecule conductances of similar magnitude to organic oligo( phenylene ethynylene)-and oligo(yne)-based molecular wires.…”

Programmed Synthesis of Molecular Wires with Fixed Insulation and Defined Length Based on Oligo(phenylene ethynylene) and Permethylated α‐Cyclodextrins

“…Elongated wires 5 ‐ iu and 7‐iiu showed similar maximum absorption and emission wavelengths because of their saturated effective conjugation lengths . The emission of partially insulated OPE 5 ‐ iu was blueshifted compared to completely uninsulated 5 ‐ uu , and this was attributed to the shortened effective conjugation chain length of the twisted conformation of the PE backbones on the insulated area; PM α‐CD‐based insulation afforded a twisted dihedral angle between adjacent benzene units as compared to the planar uninsulated counterparts . On the other hand, the quantum yield of 5 ‐ uu (17 %) dramatically decreased in the solid state compared to that of 5 ‐ iu (37 %) because the π–π interactions between the exposed conjugated wire in the solid state induced nonradiative quenching through disordered energy transfer.…”