Regioisomeric manipulation of AIE-active photosensitizers towards multidrug-resistant bacterial eradication†

Multidrug-resistant (MDR) bacterial infection is currently one of the pressing threats to human health globally. Photodynamic therapy (PDT) based on AIE-active photosensitizers (PSs) has garnered significant attention as a competitive and promising alternative for microbial elimination because of its noninvasiveness, photoswitchable controllability, and minimal drug resistance. The existing molecular engineering strategies prevailingly focus on the tuning of donor/π bridges and/or peripheral rotors. However, the regional tuning of a positively charged center, as a critical point of photosensitizers (PSs), is of great meaning but still remains rarely reported. Herein, we tactfully developed two benzoquinolizinium-based regioisomeric PSs, TPA-BQZ-1 and TPA-BQZ-2, with differently located positive charge centers. The targeted regioisomers could be obtained through a one-step facile strategy with superior step- and atom-economy, in contrast to the widely developed linear-shaped D–π–A type antibacterial PSs, which require stepwise sequential binding of different functional segments via multi-step coupling reactions. The distinctive molecular structures endowed TPA-BQZ-1 and TPA-BQZ-2 with typical AIE features and high-efficiency ROS output ability by both type I and type II pathways. Both regioisomeric PSs could achieve effective MDR bacterial eradication yet dominated by different pathways, highlighting the critical role of the positively charged position in antibacterial PSs. By comparison, the antibacterial performance of TPA-BQZ-1 is dominated by phototoxicity. Conversely, the intrinsic dark toxicity of TPA-BQZ-2 exerted a great influence on the antibacterial efficiency, maybe stemming from the strong membrane interaction and the resulting membrane permeability. This study demonstrates an ingenious regioisomeric engineering strategy and offers useful guidance for the development of advanced antibacterial agents.