Quadruple Anticounterfeiting Encryption: Anion-Modulated Forward and Reverse Excitation-Dependent Multicolor Afterglow in Two-Component Ionic Crystals.

Molecule-based afterglow materials with ultralong-lived excited states have attracted great attention owing to their unique applications in light-emitting devices, information storage, and anticounterfeiting. Herein, a series of new types of two-component ionic crystalline materials were fabricated by the self-assembly of cytosine and different anions under ambient conditions. The multiple intermolecular interactions of cytosine with phosphate and halogens anions can lead to abundant energy levels and different crystal stacking modes to control molecular aggregation and excited-state intermolecular proton transfer (ESIPT) process. Interestingly, H-aggregation-induced green to yellow room-temperature phosphorescence (RTP) and ESIPT-dominated cyan RTP to deep blue thermally activated delayed fluorescence (TADF) emission can be generated by tuning excitation wavelength, time evolution, and temperature. Furthermore, the combination of two-component ionic crystals can be used as multicolored candidates for quadruple information encryption. Therefore, this work not only develops an anion-modulated strategy to achieve color-tunable afterglow from both static and dynamic fashions but also provides a guideline for designing forward/reverse excitation-dependent luminescent materials.