Molecular Engineering Enables Multi‐Color Room Temperature Phosphorescence of Carbon Dots Composites Derived In Situ, Facilitating their Utilization for Advanced Information Encryption

Abstract Long‐life room temperature phosphorescent (RTP) materials hold significant potential in the fields of optoelectronic devices, information encryption, and bio‐imaging due to their excellent optical properties. However, achieving multi‐color tunable RTP materials has proven challenging. In this study, molecular engineering strategies are employed to select precursor molecules with varying degrees of conjugation such as phthalic anhydride (PA), naphtho[2,3‐c] furan‐1,3‐dione (23NA), and naphthalic anhydride (NA). By combining these guest molecules with a host boric acid matrix through a one‐step microwave method, carbon dots (CDs)composites (PA@BA, 23NA@BA and NA@BA) exhibiting excellent RTP properties are successfully prepared. As the degree of precursor conjugation increased gradually, the phosphorescence color modulation of the composites demonstrates satisfactory transitions from blue to yellow. Notably, CDs are derived in situ within the boric acid matrix while covalent and hydrogen bonds formed between CDs and borate matrix effectively suppress nonradiative leaps and facilitate composite RTP activation. Furthermore, the boric acid matrix acts as insulation against oxygen diffusion and prevents quenching of triplet excitons by external factors. The rationality behind phosphorescence emission mechanism and wavelength modulation is further conformed by density functional theory (DFT) calculations. Finally, CDs composites are successfully applied for advanced message encryption of text and images.