Switchable Proton Conduction Driven by UV/NIR-Induced Electron Transfer in an Inorganic-Organic Hybrid Gallium Phosphate–Oxalate Open-Framework

Abstract

Conventional proton-conducting materials often fail to meet the responsiveness and flexibility required for emerging technologies such as the Internet of Things (IoT) and robotics, driving significant interest toward the development of dynamically switchable and tunable proton conductors. Herein, we present a novel UV/NIR-responsive gallium phosphate–oxalate inorganic–organic hybrid, {(H3TPT)[Ga2(H2PO4)2(C2O4)3]·H2PO4·H3PO4}n (NEU25, TPT = 2,4,6-Tris(4-pyridyl)-1,3,5-triazine; C18N6H12) synthesized via an ionothermal decomposition–reconstruction strategy within a deep eutectic solvent (DES) system. Benefiting from abundant free phosphate groups and extensive hydrogen-bonding networks, NEU25 achieves a intrinsic proton conductivity of 6.9 × 10-4 S·cm-1 at 20 °C and 98% relative humidity (RH). Upon UV irradiation, NEU25 undergoes a photoinduced electron-transfer (PIET) process in which electrons are transferred from the oxalate/phosphate-based anionic framework to the protonated H3TPT3+ species, producing tunable H3TPT•2+ π-radical aggregates that induce a distinct color change (colorless to blue) and enhance proton conductivity by nearly five-fold to 3.4 × 10-3 S·cm-1. These radicals also facilitate efficient photothermal conversion under low-intensity near-infrared (NIR) light (808 nm, 0.23–2.00 W·cm-2), elevating the temperature from room temperature to 46–99 °C. High-intensity NIR irradiation (9.75 W·cm-2) rapidly triggers discoloration and reverses the conductivity enhancement within 1 minute via photothermally induced electron retransfer. NEU25 demonstrates good thermal and aqueous stability, rapid bidirectional photochromism, and reversible conductivity switching, offering a promising platform for remote-controlled, dynamically tunable proton conduction in next-generation smart materials and devices.