Characterization\nof Coulomb Interactions in Electron\nTransport Through a Single Hetero-Helicene Molecular Junction Using\nScanning Tunneling Microscopy

Characterization of the structural and electron transport\nproperties\nof single chiral molecules provides critical insights into the interplay\nbetween their electronic structure and electrochemical environments,\nproviding broader implications given the significance of molecular\nchirality in chiroptical applications and pharmaceutical sciences.\nHere, we examined the topographic and electronic features of a recently\ndeveloped chiral molecule, B,N-embedded double hetero[7]helicene,\nat the edge of Cu(100)-supported NaCl thin film with scanning tunneling\nmicroscopy and spectroscopy. An electron transport energy gap of 3.2\neV is measured, which is significantly larger than the energy difference\nbetween the highest occupied and the lowest unoccupied molecular orbitals\ngiven by theoretical calculations or optical measurements. Through\nfirst-principles calculations, we demonstrated that this energy discrepancy\nresults from the Coulomb interaction between the tunneling electron\nand the molecule’s electrons. This occurs in electron transport\nprocesses when the molecule is well decoupled from the electrodes\nby the insulating decoupling layers, leading to a temporary ionization\nof the molecule during electron tunneling. Beyond revealing properties\nconcerning a specific molecule, our findings underscore the key role\nof Coulomb interactions in modulating electron transport in molecular\njunctions, providing insights into the interpretation of scanning\ntunneling spectroscopy features of molecules decoupled by insulating\nlayers.