Highly-Efficient and Synergistic Antibacterial Photodynamic Therapy Effect of Ester-Linked Porous Organic Polymer and Methylene Blue.

The application of photosensitizers (PSs) in antibacterial photodynamic therapy is significantly restricted by the aggregation-caused quenching (ACQ) effect of PSs. Porous organic polymers (POPs) serve as efficient molecular carriers benefiting from its microporous structure and functional groups. Here, an ester-linked POP (e-POP) bearing benzophenone groups is prepared from 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BPTCD) and phloroglucinol (PG). It exhibits a specific surface area of 14.837 m² g^-1 and a pore size of 3.421 nm, enabling it to adsorb methylene blue (MB) molecules (MB@e-POP). The negatively-charged e-POP (containing 4.671 mmol g^-1 carboxyl groups) can attract and stably load the positively-charged MB. The adsorption of MB on e-POP conforms to the Langmuir isotherm and pseudo-second-order kinetic models, with a maximum capacity of 400.5 mg g^-1. Compared with MB and e-POP alone, MB@e-POP demonstrates a remarkable increase in the antibacterial rate, 42.42% and 19.63% higher for Escherichia coli (E. coli) and 44.62% and 25.54% higher for Staphylococcus aureus (S. aureus), respectively. The high antibacterial efficacy is ascribed to the distribution of MB within mesopores of e-POP and the synergistic effect of MB with e-POP in reactive oxygen species (ROS) generation. Thus, it achieves 99.99% antibacterial rate under 10 min light irradiation and maintains efficient sterilization even after 20 cycles of use.