Roles of Anion Photostability and Dye–Anion Interactions in Photostabilization of Aminobenzopyranoxanthene in Ionic Liquids

Aminobenzopyranoxanthene (ABPX) dyes hold considerable promise for imaging and sensing applications owing to their unique acid-responsive fluorescence switching and aggregation-induced emission properties. However, photobleaching under prolonged irradiation remains a significant limitation. In this study, the influence of ionic liquid environments on the photostability of ABPX was systematically investigated. Irradiation experiments under simulated sunlight revealed that photostabilizing performance depended strongly on the anion species of the ILs, whereas variations in cation structure exerted only a minor influence. Ionic liquids containing [NTf₂]⁻ and [BF₄]⁻ exhibited substantially enhanced photostability compared with those containing [PF₆]⁻ and [OTf]⁻. Furthermore, the stabilizing effect observed in [NTf₂]⁻-based ionic liquids was markedly reduced for sterically hindered ABPX derivatives, suggesting that close dye–anion interactions constitute an important factor governing photostabilization. DART–MS analysis further revealed the formation of new ion species in irradiated [C₄mim][OTf], indicating that photochemical transformations of ionic liquid components can occur under irradiation. These findings demonstrate that photostabilization in ionic liquid media is governed by a synergistic combination of anion properties, intrinsic photochemical stability, and microscopic dye–anion interactions. These results suggest a plausible mechanism where photochemically stable fluorinated anions preferentially organize around the cationic dye species to create a localized fluorous microenvironment that may function as a protective solvation cage. These insights provide useful guidelines for the rational design of highly photostable dye–ionic liquid systems and related photonic materials.