Electrochemical Modulation of Destructive Quantum Interference in Meta-Connected Oligo(phenylene Ethynylene) Molecular Junctions

Quantum interference provides a powerful mechanism for controlling electron transport at the molecular scale. While destructive quantum interference (DQI) in meta-connected aromatic systems offers potential for low conductance switching elements, experimental demonstration of electrochemical modulation under nonredox conditions remains limited. Here, we report the electrochemical gating of meta- and para-connected oligo(phenylene ethynylene) (OPE) molecules using electrochemical scanning tunneling microscopy in an ionic liquid environment. A direct topology-controlled comparison reveals that meta-connected OPEs exhibit reversible conductance modulations exceeding 2 orders of magnitude (∼10–3.8 to ∼10–6.4 G0) in response to gate potential, whereas para-connected analogs show only modest variations. The observed behavior is attributed to gate-induced shifting of a DQI antiresonance relative to the electrode Fermi level. These findings provide experimental validation of electrostatic control of quantum interference within a single molecular framework and establish electrochemical gating as an effective strategy for tuning interference-driven transport in molecular electronic devices.