Tunable Multi-Color Room-Temperature Phosphorescence via Melamine-Based Supramolecular Self-Assembly for Anti-Counterfeiting and Humidity Sensing

Abstract

This work presents a novel multi-component supramolecular self-assembly strategy for synthesizing tunable multi-color room-temperature phosphorescent (RTP) materials. Combining the host matrix melamine (M) with furoic acid (Fa) and introducing barium chloride, MFa-B exhibits a bright green afterglow with a phosphorescence lifetime of 233 ms and a visible afterglow duration of 1.6 s.Substituting BaCl 2 with ZnCl₂, MFa-Z displays an orange-red afterglow with a lifetime of 256 ms and a duration of 1.7 s. Additionally, its phosphorescence intensity demonstrates a strong linear correlation (R² = 0.9840) with relative humidity (RH) within 35%-75%. Further doping MFa-B with acridone (A) or acridoneacetic acid (AAc) yielded MFa-B-A and MFa-B-AAc, extending both afterglow durations to 3.0 s and shifting the emission color to cyan and blue, respectively. The enhanced RTP performance arises from the rigid supramolecular framework suppressing non-radiative transitions and the metal ions (Ba²⁺, Zn²⁺) promoting intersystem crossing (ISC) from singlet to triplet states. Structural characterization results confirm successful self-assembly and interactions between material components, while thermogravimetric analysis indicates good thermal stability. The materials' distinct emission colors and tunable lifetimes were successfully leveraged for multi-color dynamic information encryption and anti-counterfeiting. This work provides a straightforward and effective strategy for designing high-performance, multi-functional organic RTP materials.