Photoconductance Induced by Excited‐State Intramolecular Proton Transfer (ESIPT) in Single‐Molecule Junctions

Abstract Excited‐state intramolecular Proton Transfer (ESIPT) molecules have been drawing considerable attention due to their unique photophysical properties and potential applications in optoelectronic devices. Although ground and excited‐state tautomerism in various proton transfer systems associated with ESIPT has been extensively studied both experimentally and theoretically, the charge‐transport characteristics of ESIPT molecules at the single‐molecule level has been little investigated. In this work, scanning tunneling microscope‐based fixed junction technique (STM‐FJ) is employed with theoretical calculations to explore the electronic properties of SMe‐PhOH (with ESIPT properties), together with its photoconductance induced by ESIPT photocycle processes under continuous light illumination (254/275/295/310 nm). The conductance variation of SMe‐PhOH with different UV wavelengths exhibits a continuous photoconductance distribution, which is highly consistent with the results of its UV–vis absorption spectrum. Theoretical calculations indicate that the interaction between localized HOMO and delocalized LUMO of SMe‐PhOH K * ‐state gives rise to Fano resonance, thereby leading to enhanced conductance compared with its E‐state. It reveals the microscopic mechanism of ESIPT process at the nanoscale and provides a constructive perspective for optimizing the photoresponsive properties of ESIPT‐type molecules, as well as designing high‐performance single‐molecule devices.