Cationic AIEgens with large rigid π-planes: Specific bacterial imaging and treatment of drug-resistant bacterial infections

In this study, four D-π-A type cationic photosensitisers with aggregation-induced emission (AIE) properties were developed based on the electron-donating group triphenylamine and pyrene molecules acting as auxiliary electron donors and main π-bridges, as well as pyridinium salts of different charge numbers acting as electron acceptors: TPP1, MeOTPP1, TPP2 and MeOTPP2. The introduction of pyrene endowed the AIE photosensitizers with a high solid fluorescence quantum yield and long fluorescence lifetime. All four photosensitizer molecules were able to efficiently generate type I (·OH) and type II (¹O₂) under white light irradiation, achieving efficient inactivation of methicillin-resistant Staphylococcus aureus (MRSA) at low concentrations, and TPP1 and TPP2 successfully promoted wound healing in MRSA-infected mice. The introduction of a methoxy group effectively enhanced the intramolecular charge transfer effect, achieved longer wavelength absorption and fluorescence emission redshift, and effectively reduced ΔE_st thereby promoting ROS (Reactive Oxygen Species) generation. However, after the introduction of the methoxy group, the CAC (Critical Aggregate Concentration) of MeOTPP1 and MeOTPP2 became smaller and the hydrophobicity was enhanced, which affected the interaction with bacteria. In fact, the photodynamic antimicrobial activity and imaging ability against bacteria were reduced. TPP2 achieves efficient killing of MRSA and MDR E.coli (Multidrug-resistant Escherichia coli) by disrupting the bacterial cell membrane due to its high photosensitization efficiency, two positive charges and very high CAC value. Under light (40 mW·cm⁻²), only 1 μM of TPP2 inactivated 87 % of MRSA, followed by TPP1, which inactivated 59 %, while MeOTPP1 and MeOTPP2 showed no significant antibacterial activity at this concentration. At a concentration of 10 μM, TPP2 deactivated more than 95 % of MDR E.coli, TPP1 deactivated about 41 %, and MeOTPP1 and MeOTPP2 had no antimicrobial activity against MDR E.coli at this concentration. In addition, TPP1, MeOTPP1 and TPP2 were able to rapidly identify MRSA and MDR E.coli under the irradiation of 365 nm UV light, which provides a visual method for the rapid identification of MRSA and MDR E.coli.