Ultra‐Long‐Lived Red TADF‐CDs: Solid‐State Synthesis, Time‐Dependent Phosphorescence Color And Luminescent Mechanism

Abstract Constructing an ultra‐long‐lived red thermally activated delayed fluorescence carbon dots (TADF‐CDs) with time‐dependent phosphorescence colors (TDPC) in both solid and aqueous is still a challenge. Herein, a red TADF‐CDs, constructed via. a modified solid‐state pyrolysis strategy, show the phosphorescence emissions at 595, 670, and 725 nm with the afterglow lifetime longer than most of reported red TADF‐materials. In addition, the resulting CDs trigger the TDPC activity while the emission colors changed from red to green both in solid state and in aqueous suspension. The synergistic effects of boron‐hybridization in the seed CDs and the additional C═O groups generated in urea‐assisted pyrolysis, result in a stronger spin‐orbit coupling (SOC) between the ¹(n, π^*) and the ³(π, π^*), the mitigated energy gap (ΔE_ST) and the non‐radiative relaxations of triplet excited states. The TDPC performance endow the resulting TADF‐CDs the usability in advance information security with enhanced‐security‐level encryption strategy.