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

Abstract 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.