Enhancing near-infrared AIE of photosensitizer with twisted intramolecular charge transfer characteristics via rotor effect for AIE imaging-guided photodynamic ablation of cancer cells.

Near-infrared (NIR) aggregation-induced emission (AIE) of previous organic photosensitizers is usually weak because of the competition between twisted intramolecular charge transfer (TICT) effect and AIE. Herein, we report a rational molecular design strategy to boost NIR AIE of photosensitizers and still to keep strong 1O2 production capacity via rotor effect. To this end, one new triphenylamine (TPA)-based AIE photosensitizer, TPAM-1, is designed to give strong ability to generate 1O2 but weak NIR fluorescence in the aggregate state due to the strong TICT effect. Another new TPA-based AIE photosensitizer, TPAM-2, is designed by introducing three p-methoxyphenyl units as rotors into the structure of TPAM-1 to modulate the competition between AIE and TICT. TPAM-1 and TPAM-2 exhibit stronger ability to generate 1O2 in the aggregate state than the commercial photosensitizer, Ce6. Furthermore, TPAM-2 gives much brighter NIR luminescence (25-times higher quantum yield) than TPAM-1 in the aggregate state due to the rotor effect. TPAM-2 with strong NIR AIE and 1O2 production capability was encapsulated by DSPE-PEG2000 to give good biocompatibility. The DSPE-PEG2000-encapsulated TPAM-2 nanoparticles show good cell imaging performance and remarkable photosensitive activity for killing HeLa cells. This work provides a new way for designing ideal photosensitizers for AIE imaging-guided photodynamic therapy.