In-situ formation of one-dimensional coordination polymers in molecular junctions

Abstract

We demonstrate the bottom-up in-situ formation of organometallic oligomer chains at the single-molecule level. The chains are formed using the mechanically controllable break junction technique operated in a liquid environment, and consist of alternating isocyano-terminated benzene monomers coordinated to gold atoms. We show that the chaining process is critically determined by the surface density of molecules. In particular, we demonstrate that by reducing the local supply of molecules within the junction, either by lowering the molecular concentration or by adding side groups, the oligomerization process can be suppressed. Our experimental results are supported by ab-initio simulations, confirming that the isocyano terminating groups display a high tendency to form molecular chains, as a result of their high affinity for gold. Our findings open the road for the controlled formation of one-dimensional, single coordination-polymer chains as promising model systems of organometallic frameworks.

In situ formation of H-bonding imidazole chains in break-junction experiments

“…However, many compounds which have been measured as single-entity junctions in the literature might be capable of forming H-bonded chains, but evidence of in situ formation of oligomeric entities during a break-junction experiment is scarce. Examples of such oligomerisation processes available in the literature are limited to those involving coordination or chemical bonds, such as metallopolymers formed by abstraction of metal atoms from the two electrodes, 37 spontaneous dimerization of organotin compounds, 38 and, recently, fieldinduced catalytic oligomerisation of terminal anilines. 39 We believe the peculiar behaviour of imidazole can be attributed to its particularly high moment of dipole, measured at 3.67 D (as comparison, H 2 O = 1.83; HCN = 2.98; acetonitrile = 3.44).…”

Single-molecule functionality in electronic components based on orbital resonances

“…To date, a large range of such functionalities have been realized experimentally, with molecules being employed as transistors, 3,18,[29][30][31] diodes, [32][33][34][35][36][37][38][39] resonanttunneling diodes, 40 switches, 12,13,41,42 light-emitters, 43 photoresponsive devices, 44 memory elements, 45 thermoelectric power generators, 14,15,46 potentiometers 47 and strain-sensors. 26 Common approaches in the design of single-molecule devices are the engineering of the coupling to the electrodes via various anchoring groups, [48][49][50][51][52] and controlling the level alignment of the molecular orbitals closest to the Fermi energy of the contacts, either by chemical means 53 or using an electrostatic gate (solid-state 3,[18][19][20][21][29][30][31] or an electrochemical [54][55][56][57] ), and the exploitation of quantum effects such as destructive interference.…”

Using Automated Synthesis to Understand the Role of Side Chains on Molecular Charge Transport

“…Recent work has reported that additional conductance states may arise from in-backbone molecule-electrode linkages, 9,[18][19][20][21] in situ dimerization, 17,[22][23][24] or intermolecular interactions. [25][26][27] To investigate the origin of the high G state, we synthesized the non-C2-symmetric terphenyl derivative R6-H containing only one terminal anchor using automated iterative cross-coupling (Fig.…”