Highly Efficient Near-Infrared Photosensitizers with Aggregation-Induced Emission Characteristics: Rational Molecular Design and Photodynamic Cancer Cell Ablation.

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Photosensitizers (PSs) that play a decisive role in effective photodynamic therapy (PDT) have attracted great research interest. PSs with aggregation-induced emission (AIE) characteristics could overcome the deficiencies of traditional PSs that usually suffer from the aggregation-caused fluorescence quenching (ACQ) effect in applications and show enhanced emission and high singlet oxygen (1O2) generation efficiency in aggregates; therefore, they are outstanding candidates for imaging-guided PDT, and the development of AIE PSs with both excellent photophysical properties and 1O2 generation ability is highly desirable. Herein, three AIE fluorogens (AIEgens), BtM, ThM, and NaM, with a donor-π-acceptor (D-π-A) structure were designed and synthesized, and the photosensitizing ability was adjusted by π-linker engineering. All of the three AIEgens showed excellent photostability and high molar absorption coefficients, and their emission edges were extended to the near-infrared (NIR) region, with peaks at 681, 678, and 638 nm, respectively. NaM demonstrated the smallest ΔES1-T1, which was ascribed to its better separation degree of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The AIEgens were fabricated into nanoparticles (NPs) by amphipathic mPEG3000-DSPE encapsulating, and thus the obtained NaM NPs exhibited the best 1O2 generation efficiency under white light irradiation, which was almost 3 times that of the renowned PS rose bengal (RB). Furthermore, under white light irradiation, the cell killing efficiency of NaM NPs was also much better than those of the other two AIE PSs and RB. Therefore, NaM NPs revealed great potential to treat superficial diseases as a PS for PDT.