Ionic gating of a meta-connected molecular junction achieves a 105 ON/OFF ratio

Abstract

Molecular architectures featuring stable radical centres and tunable π-conjugated backbones are well-established platforms for investigating charge transport at the single-molecule level. In this study, we examine the transport characteristics of three established connectivities para-connected, ortho-connected, and doubly π-bridged ortho based on bis(triarylamine) organic analogues, in the presence of counter-ions positioned at various locations around the molecular framework. These systems provide a platform for assessing how structural connectivity governs quantum interference and how local electrostatic perturbations influence the transmission spectrum. Building on these benchmarks, a new meta-connected variant is proposed and its behaviour in the presence of counter ions is evaluated. In contrast to the para and ortho arrangements, which display only modest variations under ionic perturbation, the meta configuration exhibits a markedly enhanced response. Depending on the ion's position, the transmission is either significantly suppressed or strongly modulated by nearly five orders of magnitude producing an ON/OFF ratio of ∼10⁵. This pronounced switching arises from the destructive interference inherent to meta connectivity and its susceptibility to local electrostatic fields. Overall, the results demonstrate that meta-engineered molecular junctions offer a highly sensitive route for ion gated control of charge transport, with promising implications for molecular scale electronic switching and sensing technologies.