Molecular engineering to accelerate cancer cell discrimination and boost AIE-active type I photosensitizer for photodynamic therapy under hypoxia

The severe hypoxia in solid tumor and the accurate discrimination between cancer and normal cells gravely restrict the application of fluorescence imaging-guided photodynamic therapy (PDT), although this cancer-therapy modality has significant superiorities in terms of precise visualization of the location of photosensitizers (PSs) in tumor tissue as well as noninvasive and reliable treatment. A convenient and universal fluorescence system featuring Type I reactive oxygen species (ROS) based on free radicals, wide-spectrum cancer cell discrimination and distinctive aggregation-induced emission (AIE) characteristics could offer a feasible approach to resolve the problems above, which is yet extremely challenging. Herein, we propose a series of electron-rich anion-π+ AIE-active luminogens (AIEgens) fabricating increasingly stronger intermolecular charge transfer (ICT) state to promote highly efficient intersystem crossing for boosting Type I ROS generation. Moreover, MeOTPPM has priority to enter cancer cells with better plasma membrane permeability due to the strongest binding force with water molecules. This work serves as a pioneering reference for rationally constructing Type I-based purely organic PSs to overcome tumor hypoxia defects in PDT and selectively targeting and ablating cancer cells over normal cells without the aid of any extra cancer cell-specific targeting ligands.