Achieving thermal-stimulus-responsive dynamic afterglow from carbon dots by singlet-triplet energy gap engineering through covalent fixation

Integrating stimuli-responsive luminescence with dynamic emission properties offers a powerful strategy to enhance information encryption through multi-level authentication systems. By rationally tuning the singlet-triplet energy gap (Δ E ST ) of a material, simultaneous activation of phosphorescence (Phos) and delayed fluorescence (DF) can be achieved, enabling programmable dynamic afterglow behavior. In this work, we report the first carbon dot (CD)-based thermoresponsive dynamic afterglow material, synthesized via in situ covalent immobilization of CDs within a cyanuric acid matrix. The resulting system demonstrates a thermally driven green-to-blue afterglow transition across a wide temperature range (273.15–423.15 K), exhibiting dual-mode thermochromic afterglow (TCA) and time-resolved afterglow (TRA) characteristics. Notably, a blue-to-green afterglow transition occurs above the threshold temperature of 348.15 K, where TRA dominates due to temperature-dependent exciton redistribution. This synergistic TCA-TRA interplay endows the material with unprecedented dynamic afterglow modulation capabilities. Structural and photophysical analyses confirm that covalent fixation reduces the Δ E ST of CDs from 0.46 to 0.28 eV, as designed. This ΔE ST engineering enables thermal control over the Phos/DF equilibrium, directly governing the observed dynamic emission. Finally, the potential applications of the prepared material in thermal monitoring and high-security information protection are also demonstrated.