Precise Control of Fano Resonance through Molecular Design: Enhancing Electron Transport Property in Single-Molecule Junctions

Fano resonance, a distinctive quantum interference phenomenon, offers unprecedented advantages in modulating electron transport efficiency within single-molecule junctions. However, limited understanding of the relationship between electronic structure and Fano resonance characteristics has hindered optimization of quantum transport properties for molecular devices. In this study, we systematically investigated a series of fluorene derivatives featuring tunable side groups connected to the molecular backbone while isolated from electrodes, successfully achieving Fano resonance. Based on density functional theory (DFT) with non-equilibrium Green's function (NEGF) calculations, we showed that substituent-dependent modulation of localized orbital energies and backbone-side chain electronic coupling can precisely control the Fano resonance valley position (Eposition=|Evalley-EF|) and peak-valley width (Ewidth=|Evalley-Epeak|). By exploiting this mechanism, we achieved concurrent theoretical enhancement of conductance and Seebeck coefficient, with both parameters exhibiting approximately 20-fold increases. Furthermore, electrochemical scanning tunneling microscopy break junction (EC-STM-BJ) measurements of C-CN molecules experimentally confirmed the predicted Fano resonance features near the Fermi level. These findings provide a robust molecular structure-Fano resonance control mechanism and crucial foundations for developing advanced single-molecule devices, including molecular transistors and innovative gate-controlled molecular thermoelectric devices.