Anthraquinone-Centered Type I Photosensitizer with Aggregation-Induced Emission Characteristics for Tumor-Targeted Two-Photon Photodynamic Therapy

Exploring advanced photodynamic strategies to surmount the firm reliance on oxygen and the limited penetration depth of excitation light is of great significance in tumor therapy. Herein, a two-photon excitable type I photosensitizer with aggregation-induced emission characteristics, namely tBuT2AQ, is rationally designed by simply equipping an anthraquinone (AQ) acceptor with the rotor-type electron-donating triphenylamine derivatives. The AQ moiety with good electron-withdrawing ability and significant spin–orbit coupling effect could facilitate the generation of triplet excitons by triggering multichannel intersystem crossing. These triplet excitons could further undergo electron transfer processes and enable massive production of type I reactive oxygen species because of the redox cycling behaviors mediated by carbonyl groups in the AQ moiety. Moreover, the planar structure of the AQ moiety is beneficial for two-photon excitation and allows for deep penetration into biological tissues. After being formulated into nanoparticles with acid-responsive charge-reversible polymers, tBuT2AQ can be accumulated at the tumor sites efficiently and performs highly effective treatment.