Fully Reversible Photoelectronic Switching Enabled by Delocalized Excitons in a Single Superatom Junction

Single-molecule switches, the smallest fundamental components of nearly all electronic devices, represent an essential pathway toward device miniaturization and multifunctionality. However, achieving fully reversible, robust, and atomically precise photoelectronic switching remains a grand challenge. Herein, we introduce a class of gate-controlled and reversible single-cluster photoelectronic switches based on ligand-protected M@Au₁₂ (M is a heteroatom dopant) superatoms. The electronic coupling between the dopant atom and the Au₁₂ cage leads to distinct superatomic configurations, which modulate the energy barrier for electron transfer upon photoexcitation. The superatomic clusters with a valence electron count of 18 exhibit strong excitonic delocalization that induces a large dipole moment. When covalently anchored between gold electrodes via halide linkers, the single-cluster junction enables fully reversible photoconductive behavior with contact-resistance ratios of 10⁴-10⁵ between dark and illuminated states under a low gate voltage (0.50 V). These results provide vital insights into the design of molecular switches with low power consumption, ultrafast response, and high on/off ratios, paving the way for atomic-scale manufacturing.