Voltage-Induced Single-Molecule Junction Planarization

Abstract

Probing structural changes of a molecule induced by charge transfer is important for understanding the physicochemical properties of molecules and developing new electronic devices. Here, we interrogate the structural changes of a single diketopyrrolopyrrole (DPP) molecule induced by charge transport at a high bias using scanning tunneling microscope break junction (STM-BJ) techniques. Specifically, we demonstrate that application of a high bias increases the average nonresonant conductance of single Au−DPP−Au junctions. We infer from the increased conductance that resonant charge transport induces planarization of the molecular backbone. We further show that this conformational planarization is assisted by thermally activated junction reorganization. The planarization only occurs under specific electronic conditions, which we rationalize by ab initio calculations. These results emphasize the need for a comprehensive view of single-molecule junctions which includes both the electronic properties and structure of the molecules and the electrodes when designing electrically driven single-molecule motors.

Unraveling current-induced dissociation mechanisms in single-molecule junctions

“…These findings may also be interesting in the context of recent experimental studies which showed the change of the transport characteristics related to bond rupture and structural changes. 17,19,111,112 Although the time-scales observed in the experiments are significantly longer than in our study, 111 the basic relation between a structural change of the molecule and the time-dependent change of the current-voltage characteristic should appear similar.…”

Nonequilibrium reaction rate theory: Formulation and implementation within the hierarchical equations of motion approach

“…Examples include chemical reactions induced in scanning tunneling microscopy (STM) experiments at molecule-metal interfaces [20][21][22][23][24][25][26][27] as well as current-induced chemical reactions in single-molecule junctions. [28][29][30][31][32][33][34] To study chemical reactions in such scenarios, we have recently proposed a fully quantum mechanical simulation scheme, based on the hierarchical equations of motion (HEOM) approach. [35][36][37] Applications to current-induced bond rupture at metal surfaces, a process which is closely related to the breakdown of molecular functionalities, [38][39][40][41] showed that the HEOM method provides an accurate and efficient description of this process at high bias voltages.…”

Single‐Molecule Charge‐Transport Modulation Induced by Steric Effects of Side Alkyl Chains

“…[3] However, it remains challenging to distinguish the contribution of the sidechain on the intramolecular charge transport and the intermolecular packing. For that, the charge transport through the single-molecule diketopyrrolopyrrole (DPP) junctions [4] provides a unique opportunity to study the role of the side-chain on the intramolecular charge transport from the single-molecule level.…”

“…In charge-transport investigations through single-molecule junctions, conjugated molecules typically possess alkyl chains as soluble groups attached to the periphery of conjugated cores to have solubility for the processing and characterization. [4][5][6] In some cases, studies suggested that the side-chains attached to the rigid oligo-phenylene-ethynylene (OPE) building blocks lead to no significant changes in the electronic structure of the conjugated backbone, and thus alkyl chains are replaced by methyl groups in most of the combined theoretical investigations. [6] However, the role of the side-chains on the conformation control of the conjugated frameworks remained unexplored.…”