Ester-Modified Dicyanoaniline Derivative with Tunable Afterglow via Polymer Matrix and Thermal Annealing for Dynamic Encryption and Iron(III) Detection

This study develops a pure organic phosphor, Me-ADBD, which exhibits dual-state emission by combining thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP). Through a host–guest doping strategy using PMMA and PVA matrices, the phosphorescence emission wavelength, TADF/RTP intensity ratio, and afterglow duration are effectively tuned. Optimized 1% Me-ADBD@PMMA and 1% Me-ADBD@PVA films achieve afterglow durations of 6 and 7 s, respectively. Thermal treatment at 150 °C further enhances the performance of PVA-based films, extending the afterglow to 10 s and improving water resistance. The material also demonstrates sensitive Fe3+ detection based on afterglow quenching, enabling instrument-free visual analysis. Theoretical calculations reveal that a small singlet–triplet energy gap (ΔEST2 = 0.51 eV) and strong spin–orbit coupling facilitate efficient TADF. Finally, multilevel anticounterfeiting and dynamic information encryption are constructed. This work provides insights into designing versatile organic phosphors for advanced optical applications.