Ionic Liquid-Mediated Ionothermal Synthesis of a Multifunctional Photochromic Gallophosphate

A multifunctional crystalline gallophosphate, |C₁₀N₂H₉|[Ga(PO₄)(H₂PO₄)] (NEU26), was synthesized via an ionothermal strategy employing tetrabutylammonium phosphate as a versatile ionic liquid that simultaneously functions as the reaction medium and phosphorus source, while exerting solvent-mediated microenvironment modulation during crystallization. This approach demonstrates, for the first time, the feasibility of constructing photochromic gallophosphate open-frameworks using a nonphotoactive organic template, 4,4'-bipyridine, in combination with a multifunctional ionic liquid to streamline the synthesis. The one-dimensional open-framework of NEU26 exhibits distinct and reversible UV-induced photochromism, attributed to photoinduced electron transfer from inorganic anionic chains to monoprotonated Hbpy⁺ species, generating tunable colored Hbpy^· radicals. Leveraging both its photochromic behavior and intrinsic photoluminescence, NEU26 integrates multiple functionalities, including light-gated fluorescence modulation (on/off ratio of 13:1), UV dosimetry, erasable inkless printing, and anticounterfeiting encryption. This study highlights the synthetic utility of multifunctional ionic liquids in the targeted construction of advanced hybrid frameworks and offers new insights into the rational design of responsive, multifunctional materials.