High-performance room-temperature molecular switches enabled by resonant tunnelling in dithia-porphyrins

Abstract

Achieving stable and reproducible single-molecule switches at room temperature remains a key challenge in molecular electronics. Conventional porphyrins, while attractive for their conjugated framework and versatile redox chemistry, often exhibit wide HOMO–LUMO gaps, weaker electrode coupling, and unstable redox states, limiting their switching performance. Here, we demonstrate that core-modified 21,23-dithia-porphyrins (N₂S₂-porphyrins) overcome these limitations by introducing sulfur atoms into the porphyrin core. This strategic modification lowers the HOMO–LUMO gap (better conduction), enhances orbital coupling with soft Hg electrodes, and, most importantly, stabilizes redox states that act as reliable molecular switching centers. When integrated as self-assembled monolayers on silicon, N₂S₂-porphyrins produce small-area MMS junctions that exhibit room-temperature bistable I–V behaviour with ON/OFF ratios >20, narrow SET thresholds (∼0.6 V), and stability over 1000 cycles. Supported by DFT–NEGF calculations, these results establish core-modified dithia-porphyrins as superior to conventional porphyrins for molecular-scale memory and logic devices. This study positions core-modified dithia-porphyrins as a new molecular design paradigm, where stable redox chemistry and improved device reproducibility converge to realize practical room-temperature molecular electronics.