Stable Synapse-Like Memory Switching in N-Heterocyclic Carbene Monolayers.

Das A; Borrini A; Gutheil C; Braunschweig B; Shakhayeva B; Katsoukis G; Nieuwenhuis AF; Ahmed R; Leitherer S; Solomon GC; Glorius F; Nijhuis CA

Abstract

We report a robust redox-active N-heterocyclic carbene (NHC) monolayer that exhibits synapse-like behavior driven by proton-coupled electron transfer (PCET). Our quinone-functionalized NHC (Rex-NHC) forms densely packed, upright self-assembled monolayers (SAMs) on Au, confirmed by cyclic voltammetry, x- ray photoelectron spectroscopy, sum-frequency generation spectroscopy, and infrared reflection absorption spectroscopy. Molecular junctions built as Au-Rex-NHC//Ga2O3/EGaIn operate over ± 2 V and can withstand electric fields up to 3.3 GV/m. Bias-induced PCET toggles between quinone (off) and hydroquinone (on) states, yielding reversible hysteresis with on/off ratios up to 1.9 × 102. The devices exhibit spike-timing and spike-rate-dependent plasticity, demonstrating for the first time molecular-level neuromorphic behavior using NHCs as anchoring groups.