Light-Controlled Electrostatics at Redox-Active Metal–Organic Framework Heterointerfaces

Interfacial electrostatics are central to charge separation, catalysis, sensing, energy conversion, and electronic transport, but the built-in potential of heterojunctions is generally considered fixed by the constituent materials. Here we show that redox-active metal–organic framework (MOF) heterointerfaces enable reversible optical control over the junction electrostatics. A heterostructured thin film assembled from n-type Cu-BHT (BHT = benzenehexathiol) and p-type Cu-ADA (ADA = azobenzenedicarboxylate) exhibits pronounced current rectification together with a light-induced increase in the cut-in voltage by ∼0.9 V. Spectroscopic measurements identify Cu(I) centers and sulfur radical anions as photoactive redox sites. Combined electrical measurements and density functional theory calculations reveal substantial interfacial charge reconstruction and a Type-I band alignment that confines photogenerated holes near the junction. This charge accumulation expands the depletion region and increases the built-in potential, as corroborated by the capacitance–voltage measurements. Our findings establish MOF heterojunctions as chemically programmable platforms for dynamic control of interfacial electrostatics and adaptive optoelectronic functionality.