AIE-active luminogens as highly efficient free-radical ROS photogenerator for image-guided photodynamic therapy

Image-guided photodynamic therapy (PDT) can realize highly precise and effective therapy via the integration of imaging and therapy, and has created high requirements for photosensitizers. However, the PDT modality usually utilizes conventional type II photosensitizers, resulting in unsatisfactory imaging and therapeutic outcomes due to aggregation-caused quenching (ACQ), "always on" fluorescence and strong oxygen dependence. Herein, we report the type I-based aggregation-induced emission (AIE) photosensitizer TCM-CPS with low oxygen dependence, near-infrared (NIR) emission and "off-on" fluorescence; in particular, it produces more reactive oxygen species (ROS) than commercially available Chlorin e6 and Rose Bengal. In the rational design of the AIE-based photosensitizer TCM-CPS, the strongly electron-donating carbazole unit and pi-thiophene bridge distinctly extend the emission wavelength and decrease the autofluorescence interference in bio-imaging, and the hydrophilic pyridinium salt group guarantees good molecular dispersion and maintains the fluorescence-off state in the aqueous system to decrease the initial fluorescence background. Moreover, the strong donor-pi-acceptor (D-pi-A) character in TCM-CPS greatly separates the HOMO-LUMO distribution, enhancing the ROS generation, and TCM-CPS was constructed as a type I photosensitizer with the assistance of strong intramolecular charge transfer in the electron-rich anion-pi(+) structure. Based on its favorable hydrophilicity and photosensitivity, TCM-CPS was found to be a highly efficient free-radical ROS photogenerator for both visualizing cells using light-up NIR fluorescence and efficiently killing cancer cells upon light irradiation. The positively charged TCM-CPS could quickly bind to bacteria via electrostatic interactions to provide a light-up signal and kill bacteria at a low concentration. In the PDT treatment of bacteria-infected mice, the mice exhibited accelerated wound healing with low wound infection. Thus, the AIE-based type I photosensitizer TCM-CPS has great potential to replace commercially available photosensitizers in the image-guided PDT modality for the treatment of cancer and bacterial infection.