Influencing the conductance in biphenyl-like molecular junctions with THz radiation

TL;DR

This study explores how THz radiation influences conductance in biphenyl-like molecular junctions, showing that functional groups enable external fields to modulate torsional angles and current, especially at resonance frequencies.

Contribution

It demonstrates that adding functional groups introduces dipole moments allowing external THz fields to control torsional angles and conductance in biphenyl-like molecules, supported by ab-initio calculations and a proposed model.

Findings

External THz fields have minimal effect on unmodified biphenyl junctions.

Functional groups induce dipoles, making the molecules responsive to THz fields.

Resonance with torsional vibration modes significantly alters current.

Abstract

We investigate the torsional vibrations in biphenyl-like molecular junctions and transport properties in the presence of an external THz field. Ab-initio calculations including external electric fields show that the torsional angle {\phi} of a thiolated biphenyl junction exhibits virtually no response. However, if functional groups are added to the molecule, creating a dipole moment in each of the rings, an external field becomes more effective for changing {\phi}. A model based on the cos2{\phi} dependence of the current is proposed for the biphenyl-like molecular junctions in presence of an external THz field including 2,2'-bipyridine, 3,3'-bipyridine and 2,2',4,4'- tetramethyl-3,3'-bipyridine. The current through these molecules is shown to change if the THz frequency gets in resonance to the torsional vibration mode.