State-selective engineering in luminescent metal-organic frameworks: Ligand-to-ligand charge transfer activates superior photocatalytic sterilization in Wei River.

Aggregation-induced emission (AIE) materials hold significant promise for photocatalytic sterilization. However, poor water solubility and separation of photoexcited carriers limit their applications. To address these issues, we incorporated 1,1,2,2-Tetra (4-carboxyphenyl) ethylene (TPE) ligands into metal-organic frameworks (MOFs), tuning ligand ratios to synthesize a series of Zn-TPE frameworks (Zn-TPE 1-4). Remarkably, Zn-TPE-3 exhibited the lowest water contact angle (37.10 ± 1.24°) and the longest fluorescence lifetime (5.60 ns), indicating enhanced hydrophilicity and suppressed carrier recombination. Based on X-ray absorption fine structure spectroscopy and density functional theory calculations, Zn-TPE-3 features dual-Zn clusters bridged by carboxylates from four TPE ligands. Spatial orbital overlaps between adjacent TPE ligands enabled a ligand-to-ligand charge transfer mechanism, facilitating directional separation via a dominant photoactive S3 state (oscillator strength f = 1.98) while circumventing the symmetry-forbidden S1 pathway. These properties enabled effective interactions with bacteria and superior reactive oxygen species generation, yielding 3.90 and 6.54 log10 CFU/mL reductions against S. aureus and E. sakazakii compared to TPE alone. Furthermore, the state-selective Zn-TPE-3 demonstrated complete elimination of microorganisms in Wei River water samples within 60 min. The work presents a novel MOF engineering strategy that amplifies AIE photosensitizer performance, advancing highly efficient photocatalytic antibacterial systems.