Flexible Double Bonds-Enhanced Photodynamic Therapy toward Antibacterial Resistance

The relationship between the molecular structure and types of reactive oxygen species (ROS) generated from photosensitizers (PSs) must be understood for advancing photodynamic therapy (PDT). In this study, we synthesized PS-S⁺, PS-D⁺, and PS-T⁺ consisting of C-C, C═C, and C≡C bond linkers, respectively, between electron donor and acceptor moieties. Unlike PS-S⁺ and PS-T⁺, PS-D⁺ containing a flexible C═C bond linker can absorb energy under white light irradiation, which enhances the swing of connected acceptor groups and leads to the formation of a noncoplanar structure. ROS generation experiments and density functional theory (DFT) calculations demonstrated that the formed noncoplanar structure of PS-D⁺ can narrow the energy gap between the singlet and triplet states (ΔE_S-T), which facilitated intersystem crossing, thereby enhancing ROS production, and shifted the generation mechanism from Type II to Type I. PS-S⁺, PS-D⁺, and PS-T⁺ antibacterial fibers were synthesized using the wet spinning method. Our developed fibers exhibited long-term, good antibacterial properties in both in vitro (Escherichia coli and Staphylococcus aureus) and in vivo (infected mice) wound dressing experiments, showcasing potential as sustainable and biosafe wound dressings to accelerate healing. We herein highlight the (1) guidance for the design strategy of PS and (2) the innovative fibers for medical applications.