Molecular switch controlled by pulsed bias voltages

TL;DR

This paper proposes a conformational reorientation mechanism, driven by pulsed bias voltages, to explain the controlled switching of molecular conductance in BPDN-DT, challenging the polaron formation explanation.

Contribution

It introduces a new conformational reorientation model for molecular switching, supported by electronic structure calculations and qualitative IV reproduction.

Findings

Rejection of polaron formation as the switching mechanism.

Identification of a conformational rotation path with high energy barriers.

Qualitative agreement of theoretical IVs with experimental data.

Abstract

It was observed in recent experiments that the current-voltage characteristics (IV) of BPDN-DT (bipyridyl- dinitro- oligophenylene- ethynylene- dithiol) can be switched in a very controlled manner between "on" and "off" traces by applying a pulse in a bias voltage, V_bias. We have calculated the polaron formation energies to check a frequently held belief, namely, that the polaron formation can explain the observed bistability. Our results are not consistent with such a mechanism. Instead, we propose a conformational reorientation. The molecule carries an intrinsic dipole moment which couples to V_bias. Ramping V_bias exerts a force on the dipole that can reorient ("rotate") the molecule from the ground state ("off") into a metastable configuration ("on") and back. By elaborated electronic structure calculations, we identify a specific path for this rotation through the molecule's conformational phase space. We show that this path has sufficiently high barriers to inhibit thermal instability but still the molecule can be switched in the voltage range of the junction stability. The theoretical IVs reproduce qualitatively the key experimental observations. We propose, how the alternative mechanism of conductance switching can be experimentally verified.