Year: 2026
Type: preprint
Abstract: Enhancing the thermoelectric power factor of single-molecule junctions requires simultaneously achieving high electrical conductance and thermopower, which are often mutually constrained. The sharp and asymmetric transmission features produced by Fano resonances offer a promising strategy for mitigating this trade-off. However, quantitative molecular structure–line-shape relationships linking molecular modifications to the resonance valley position and peak-valley energy width remain underexplored. Here, we demonstrate a molecular engineering strategy based on electronically tunable 9-fluorenylidene derivatives to tailor Fano resonance line shapes in single-molecule junctions. Systematic density functional theory and non-equilibrium Green’s function (DFT-NEGF) calculations reveal that substituent-induced variations in local orbital energies, backbone-side-chain coupling and localized-delocalized state detuning control the resonance valley position and the peak-valley energy width. Specifically, the valley position correlates linearly with the energy level of the side-group-localized LUMO, whereas the width is governed by the combined effect of main-side-chain coupling and localized-delocalized state detuning. Together, these two orbital descriptors provide a practical basis for the predictive molecular engineering of Fano resonance line shapes. To experimentally validate this strategy, we synthesized and characterized the designed dicyanomethylene-substituted derivative C -(CN) 2 alongside a control molecule A -O . Electrochemically controlled scanning tunneling microscope break-junction (EC-STM-BJ) measurements confirm the emergence of Fano resonance features near the Fermi level for C -(CN) 2 , in agreement with the DFT-NEGF prediction, whereas no comparable features is observed for A -O. Crucially, statistical single-molecule conductance and thermopower measurements reveal that C -(CN) 2 simultaneously exhibits higher conductance ( G ) and Seebeck coefficient ( S ) than A -O , overcoming the usual trade-off between these two parameters. This synergy effect yields a 97.6% enhancement in thermoelectric power factor ( GS 2 ) relative to control systems. By establishing explicit structure–line-shape–property relationships, this work provides a practical molecular engineering strategy for engineering Fano resonances in single-molecule thermoelectrics.
Source: ChemRxiv
Language: English
Subfield: Electrical and Electronic Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7221650565