Boosting Solid-State Luminescence of Thiazolothiazole Viologen by Incorporating Metal Halide Clusters to Hinder π-Stacking

A new strategy is developed herein to improve the solid fluorescence of thiazolothiazole viologen by using the ZnCl₄^2- cluster as a scaffold to hinder π-stacking. Importantly, the Cl···H bonds are formed in the solid state to sustain the framework and can be automatically dissociated when dissolved in H₂O, thus having no impact on the strong emission in aqueous solution. As such, the first case of organic-inorganic viologen-zinc halide named 4PV·ZnCl₄ was designed and synthesized, and a significant increase in photoluminescence quantum yield (Φ_F) is realized from 4PV·2Br (Φ_F = 0%) to 4PV·ZnCl₄ (Φ_F = 27.0%) in solid and from 97% to 98% in H₂O. 4PV·ZnCl₄ also displays pH stimuli-responsive naked-eye chromic behavior and photoluminescence with different coloring states and intensities. The multifunctional performance of 4PV·ZnCl₄ provides a prerequisite for carrying different information, expanding their promising application in multilevel information encryption.