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

Area of Science:

• Photophysics and molecular electronics
• Single-molecule electronics
• Organic optoelectronics

Background:

• Excited-state intramolecular proton transfer (ESIPT) molecules possess unique photophysical properties relevant to optoelectronic devices.
• While ESIPT tautomerism is well-studied, single-molecule charge transport in these systems remains underexplored.

Purpose of the Study:

• To investigate the electronic properties and photoconductance of SMe-PhOH, an ESIPT molecule, at the single-molecule level.
• To elucidate the nanoscale mechanism of ESIPT-induced photoconductance under UV illumination.

Main Methods:

• Utilized scanning tunneling microscope-based fixed junction (STM-FJ) technique.
• Performed theoretical calculations to complement experimental findings.
• Examined photoconductance under continuous UV light (254/275/295/310 nm).

Main Results:

• Observed wavelength-dependent photoconductance in SMe-PhOH, correlating with its UV-vis absorption spectrum.
• Theoretical calculations revealed Fano resonance in the K* state due to HOMO-LUMO interactions, enhancing conductance.
• Demonstrated enhanced conductance in the K* state compared to the E state.

Conclusions:

• Provided a microscopic understanding of the ESIPT process at the nanoscale.
• Highlighted the potential for optimizing photoresponsive properties of ESIPT molecules.
• Offered insights for designing high-performance single-molecule electronic devices.