Influence of Functional Groups on Charge Transport in Molecular Junctions

TL;DR

This study uses density functional theory to examine how different functional groups affect charge transport in molecular junctions, revealing that electronic effects can predict conductance changes but overall influence remains weak.

Contribution

It demonstrates how functional group chemistry principles can be applied to engineer molecular transport properties, validated by DFT calculations and experimental comparisons.

Findings

Functional groups' electronic effects predict conductance trends.

Influence of functional groups on conductance is weak.

DFT conductance values align with experiments after corrections.

Abstract

Using density functional theory (DFT), we analyze the influence of five classes of functional groups, as exemplified by NO2, OCH3, CH3, CCl3, and I, on the transport properties of a 1,4-benzenedithiolate (BDT) and 1,4-benzenediamine (BDA) molecular junction with gold electrodes. Our analysis demonstrates how ideas from functional group chemistry may be used to engineer a molecule's transport properties, as was shown experimentally and using a semiempirical model for BDA [Nano Lett. 7, 502 (2007)]. In particular, we show that the qualitative change in conductance due to a given functional group can be predicted from its known electronic effect (whether it is pi/sigma donating/withdrawing). However, the influence of functional groups on a molecule's conductance is very weak, as was also found in the BDA experiments. The calculated DFT conductances for the BDA species are five times larger than the experimental values, but good agreement is obtained after correcting for self-interaction and image charge effects.