Intrinsic Bright and Robust Phosphorescence in Sulfur Quantum Dots Enabled by π-Conjugation Engineering and Covalent Matrix Anchoring.

Achieving efficient and stable intrinsic room-temperature phosphorescence (RTP) in sulfur quantum dots (SQDs) is vital for the advancement of metal-free afterglow materials but remains scarcely explored due to the inherent challenge of low triplet state formation efficiency. Herein, an ingenious approach is presented for constructing a phosphorescent SQDs-based system (π-SQDs-MA) by integrating π-conjugated units with covalent confinement in a metaboric acid (MA) matrix. Remarkably, π-SQDs-MA exhibits intense intrinsic green RTP with a high efficiency of 19.61% and demonstrates exceptional long-term stability, along with outstanding resistance to quenching by solvents, light, oxygen, pH fluctuations, and external pressure. Detailed analyses revealed that incorporating π-conjugated units enhances the generation of effective triplet states with mixed (n, π*) and (π, π*) electron configurations, while covalent bonding between π-SQDs and MA forms a highly rigid, densely interconnected network that activates RTP by confining triplet excitons and suppressing nonradiative decay. Leveraging its phosphorescent photodynamic antibacterial therapy and inherent antibacterial properties, π-SQDs-MA exhibited potent synergistic bactericidal effects, achieving near-complete inactivation of Staphylococcus aureus and Escherichia coli within 2 min, markedly outperforming existing sterilization materials and conventional antibiotics. Additionally, multicolor afterglow is demonstrated via triplet-to-singlet energy transfer, highlighting their potential in displays and dynamic multilevel encryption.