Ionic landscapes in single-molecule electronics: shaping charge transport beyond energy level realignment

The interplay between ionic environments and single-molecule charge transport represents an emerging frontier in molecular electronics, offering critical insights into nanoscale electronic behavior and its chemical underpinnings. This review examines the multifaceted influence of ions on charge transport, extending beyond the conventional paradigm of energy level alignment achieved via electrochemical gating. Key points include the modulation of tunneling barrier shapes, molecular conformations, electrode work functions, and molecule-electrode coupling, as well as the critical roles of solvent-ion interactions, pH levels, and counterion effects. Both classical and innovative experimental approaches are evaluated to provide a comprehensive understanding of how ionic environments dynamically shape molecular electronics. The integration of theoretical and experimental frameworks is also addressed, with an emphasis on developing design principles for electrolytes and junction configurations to enable precise ionic control. The review highlights the importance of ionic effects in advancing molecular electronics, from fundamental chemical insights to practical applications, and discusses their implications in device design and experimental methodologies.