Dimerization through <i>m</i> ‐Xylylene Bridge: A Strategy for Enhanced Singlet Oxygen Generation in Benzothioxanthene Imide Photosensitizers

Comprehensive Summary Photodynamic antibacterial therapy (PDAT), with its advantages of high efficiency, controllability, and low drug resistance, has emerged as a promising research focus in the field of antibacterial treatment. Herein, we design an m ‐xylylene‐bridged benzothioxanthene imide dimer (m‐Dimer) to regulate molecular aggregation behavior. Notably, the aggregated m‐Dimer exhibits a reduced singlet‐triplet energy gap (Δ E ST ), which effectively facilitates the intersystem crossing (ISC) process and efficiently generates singlet oxygen ( 1 O 2 ) under visible light. Consequently, m‐Dimer achieves exceptional antibacterial efficacy, eradicating both Escherichia coli ( E. coli ) and Staphylococcus aureus ( S. aureus ) at a low concentration of 10 μM upon white‐light irradiation. Moreover, its excellent photostability, straightforward synthesis, and low‐cost underscore high potential for scalable PDAT applications.