Interfacial Hopping Integral as a Predictive Descriptor for Electron Transport: Saturated Alkane Junctions

Electron transport across interfaces governs a broad range of fundamental phenomena. Although orbital overlap is recognized as a key determinant, its experimental quantification remains elusive. Here, we establish the interfacial hopping integral (<i>t</i>_eld-mol), quantifying orbital overlap between contacting atoms, as a predictive descriptor of single-molecule conductance in a benchmark domain of saturated α,ω-functionalized alkane junctions. Using scanning tunneling microscopy and molecular-junction mapping technique, we correlate conductance with molecular tilt (<i>tilt</i>_mol) across π- and σ-type headgroups to extract <i>t</i>_eld-mol. We start with single-atom-thick bismuth and lead adlayers on gold, with dominant <i>p</i>-character simpler than gold's <i>d</i>-orbitals. A tight-binding model incorporating Newns-Anderson-Grimley theory yields conductance heatmaps that qualitatively match experiment results and generalize to diverse molecular junctions. Applying this model to the seminal case of alkanedithiols rationalizes literature findings of one to three conductance sets by linking them to <i>tilt</i>_mol and corresponding <i>t</i>_eld-mol variations.