Redox-Active Esters as Versatile Precursors for the In Situ Construction of Covalent Au–C(sp3) Molecular Contacts

Abstract

Constructing robust, high-conductance gold–carbon (Au–C) contacts remains a central challenge in molecular electronics. The synthesis of stable precursors capable of cleanly forming these highly reactive interfaces is particularly elusive. Here, we exploit N-hydroxyphthalimide (NHP) esters─a versatile class of redox-active esters─for the in situ formation of covalent Au–C(sp3) bonds using scanning tunneling microscope-based break junction (STM-BJ) techniques. Driven by the irreversible expulsion of CO2, which acts as a “thermodynamic spring”, NHP esters undergo single-electron transfer to generate transient carbon radicals that efficiently graft onto Au electrodes. This methodology yields molecular junctions with exceptional stability and ultrahigh conductance approaching the quantum limit of unitary transmission (∼1 G0). By translating abundant carboxylic acid feedstocks into reactive surface anchors, this work establishes NHP esters as a highly effective, sustainable toolkit for the scalable fabrication of high-performance molecular devices.