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.