The single-molecule electrical conductance of a rotaxane-hexayne supramolecular assembly

Abstract

Oligoynes are archetypical molecular wires due to their 1-D chain of conjugated carbon atoms and ability to transmit charge over long distances by coherent tunneling. However, the stability of the oligoyne can be an issue. Here we address this problem by two stabilization methods, namely sterically shielding endgroups, and rotaxination to produce an insulated molecular wire. We demonstrate the threading of a hexayne within a macrocycle to form a rotaxane and report measurements of the electrical conductance of this single supramolecular assembly within an STM break junction. The macrocycle is retained around the hexayne through the use of 3,5-diphenylpyridine stoppers at both ends of the molecular wire, which also serve as chemisorption contacts to the gold electrodes of the junction. Molecular conductance was measured for both the supramolecular assembly and also for the molecular wire in the absence of the macrocycle. The threaded macrocycle, which at room temperature is mobile along the length of the hexayne between the stoppers, has only a minimal impact on the conductance. However, the probability of molecular junction formation in a given break junction formation cycle is notably lower with the rotaxane. In seeking to understand the conductance behavior, the electronic properties of these molecular assemblies and the electrical behavior of the junctions have been investigated by using DFT-based computational methods.

Reactivity of Polyynes: Complex Molecules from Simple Carbon Rods

“…Adams and co-workers investigated reactions of ferrocene end-capped polyynes with Os 3 (CO) 11 (MeCN) and H 2 Os 3 (CO) 10 . Adams and co-workers investigated reactions of ferrocene end-capped polyynes with Os 3 (CO) 11 (MeCN) and H 2 Os 3 (CO) 10 .…”

“…Tetrayne 246 in reaction with both osmium reagents gives complex mixture of products. [108] If H 2 Os 3 (CO) 10 was used instead of Os 3 (CO) 11 (MeCN) in reaction with tetrayne 246 then products of single (252, 253) addition with simultaneous reduction were isolated. [110] Hexayne 238 gave product of twofold addition (251) in reaction with the same osmium carbonyl.…”

“…[110] Hexayne 238 gave product of twofold addition (251) in reaction with the same osmium carbonyl. Bruce and co-workers also reported an adduct 255 which was a result of reaction of unsymmetrical triyne 177 with Os 3 (CO) 11 (MeCN). [111] It was possible to next transform compound 253 into the product of double addition 254.…”

“…[6] Polyynes may be regarded as model compounds of hypothetical linear allotropic form of carbon -carbyne. Polyynes also possess a remarkable application potential as molecular wires and switches in nanoelectronics, [7][8][9][10][11] as materials for optoelectronics due to their nonlinear optical response, [12][13][14][15][16][17][18] as precursors of conducting polymers [19,20] or even in live-cells imaging and sorting. Polyynes also possess a remarkable application potential as molecular wires and switches in nanoelectronics, [7][8][9][10][11] as materials for optoelectronics due to their nonlinear optical response, [12][13][14][15][16][17][18] as precursors of conducting polymers [19,20] or even in live-cells imaging and sorting.…”

Molecular Wires with Controllable π‐Delocalization Incorporating Redox‐Triggered π‐Conjugated Switching Units

“…Linearly conjugated π‐electron systems such as polyynes or polyarylenes are often considered as models for the “molecular wires“ which can conduct electrons along the π‐system . On the other hand, they can also “wire” two chromophores at the termini.…”