Highly Conductive Single-Molecule Wires with Controlled Orientation by Coordination of Metalloporphyrins

Abstract

Porphyrin-based molecular wires are promising candidates for nanoelectronic and photovoltaic devices due to the porphyrin chemical stability and unique optoelectronic properties. An important aim toward exploiting single porphyrin molecules in nanoscale devices is to possess the ability to control the electrical pathways across them. Herein, we demonstrate a method to build single-molecule wires with metalloporphyrins via their central metal ion by chemically modifying both an STM tip and surface electrodes with pyridin-4-yl-methanethiol, a molecule that has strong affinity for coordination with the metal ion of the porphyrin. The new flat configuration resulted in single-molecule junctions of exceedingly high lifetime and of conductance 3 orders of magnitude larger than that obtained previously for similar porphyrin molecules but wired from either end of the porphyrin ring. This work presents a new concept of building highly efficient single-molecule electrical contacts by exploiting metal coordination chemistry.

Building Nanoscale Molecular Wires Exploiting Electrocatalytic Interactions

“…Effective axial coordination in Cu and Fe metallophthalocyanine to Lewis bases such as pyridine blocks has been previously demonstrated [26]. We have also exploited similar schemes to effectively bridge two metal electrodes through porphyrin-like backbones [19]. A STMbased break-junction approach [27] was used to build single-molecule wires sandwiching a metallophthalocyanine between two pyridine derivative backbones ( Figure 1B).…”

“…To determine the molecular conductance across the pyridinium functionalized with metallophthalocyanine systems, we used a previously reported method [19]. Namely, it consisted of chemically modifying a gold STM tip with 4- …”

“…It has recently been demonstrated that individual metalloporphyrin rings can be trapped in a metallic nanoscale junction through axial complexation of the metalloporphyrin metal center [19,20], and that such particular porphyrin conformation at the junction through its perpendicular axis results in an excellent metal/porphyrin/metal electronic communication [19]. Here we combine this singlemolecule wiring strategy with the above described electrocatalytic molecular platform to design a novel family of tunable and highly conducting nanoscale molecular wires.…”

High cross-plane thermoelectric performance of metallo-porphyrin molecular junctions

“…Since the in-plane electrical conductance of porphyrins is rather low, we consider ''cross-plane'' junctions in which the current flows perpendicular to the porphyrin plane. 34 A shown in Fig. 1b, a groups attached to the gold by thiol anchors, with the plane of the porphyrin stacked perpendicular to the direction of charge transport.…”

“…1b). 34,36 Since large G is desirable, the 5,15-diphenylporphyrins (w-DPP) studied in this paper contains metal atoms w = Co, Cu, Ni or Zn, which are strongly coordinated with the nitrogens of pyridyl coated gold electrodes (Fig. 1a).…”