Solvent-Fueled Anion Translocation in Crystalline Phosphonium Salt

Externally stimulated ion motion within rigid crystalline matrices has significant potential to tune the functional properties of bulk materials but is difficult to control. Here, we report a diphosphonium diiodide that allows facile solid-state solvent-driven anion translocation, providing a direct optical readout of ionic motion. The dynamic character of anion-π+ interactions enables reversible reorganization of ion pairs via exchange of co-crystallized solvent. The relocation of the iodides over the distance of 4.3 Å triggers phase transitions and transforms the configuration of the excited state, thereby switching among locally excited fluorescence (1LE), locally excited phosphorescence (3LE), and charge-transfer phosphorescence (3CT). Consequently, photoluminescence is modulated across an exceptionally wide spectral window from 415 to 650 nm. Structural and theoretical investigations reveal that noncovalent interactions with solvent molecules dictate the delicate balance between solvation, hydrogen bonding, and anion-π+ contacts. The resulting ion-migration-driven phase dynamics enable the conversion of directional solid-state motion into programmable luminescent responses, offering a new platform for sensing, information storage, and adaptive optoelectronic technologies.