title: A core-shell strategy for constructing a single-molecule junction.
abstract: Understanding the effects of intermolecular interactions on the charge-transport properties of metal/molecule/metal junctions is an important step towards using individual molecules as building blocks for electronic devices. This work reports a systematic electron-transport investigation on a series of "core-shell"-structured oligo(phenylene ethynylene) (Gn-OPE) molecular wires. By using dendrimers of different generations as insulating "shells", the intermolecular π-π interactions between the OPE "cores" can be precisely controlled in single-component monolayers. Three techniques are used to evaluate the electron-transport properties of the Au/Gn-OPE/Au molecular junctions, including crossed-wire junction, scanning tunneling spectroscopy (STS), and scanning tunneling microscope (STM) break-junction techniques. The STM break-junction measurement reveals that the electron-transport pathways are strongly affected by the size of the side groups. When the side groups are small, electron transport could occur through three pathways, including through single-molecule junctions, double-molecule junctions, and molecular bridges between adjacent molecules formed by aromatic π-π coupling. The dendrimer shells effectively prohibit the π-π coupling effect, but at the same time, very large dendrimer side groups may hinder the formation of Au-S bonds. A first-generation dendrimer acts as an optimal shell that only allows electron transport through the single-molecule junction pathway, and forbids the other undesired pathways. It is demonstrated that the dendrimer-based core-shell strategy allows the single-molecule conductance to be probed in a homogenous monolayer without the influence of intermolecular π-π interactions.
authors.affiliation: State Key Laboratory of Applied Organic Chemistry (SKLAOC), College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, 730000, China.
authors.forename: Le-Jia
authors.initials: LJ
authors.lastname: Wang
authors.forename: Kai-Ge
authors.initials: KG
authors.lastname: Zhou
authors.forename: Lin
authors.initials: L
authors.lastname: Tan
authors.forename: Hong
authors.initials: H
authors.lastname: Wang
authors.forename: Zi-Fa
authors.initials: ZF
authors.lastname: Shi
authors.forename: Guo-Ping
authors.initials: GP
authors.lastname: Wu
authors.forename: Zhu-Guo
authors.initials: ZG
authors.lastname: Xu
authors.forename: Xiao-Ping
authors.initials: XP
authors.lastname: Cao
authors.forename: Hui-Xin
authors.initials: HX
authors.lastname: He
authors.forename: Hao-Li
authors.initials: HL
authors.lastname: Zhang