Building Block for Designing Bright Type I AIE-Active Photosensitizers with Deep/Near-infrared Red Fluorescence

Bright deep red/near-infrared red (DR/NIR) active type I photosensitizers (PSs) with generating superoxide anion and hydroxyl radical have been regarded as powerful functional materials to fight the "Achilles's heel" of hypoxia from solid tumor. But some problems have still existed, for example, lacking effective molecular designed strategy or typical building block to design precisely type I PSs. In addition, the relationship between fluorescent quantum efficiency and NIR fluorescent color is inconsistent according to energy gap rule. To overcome above mentioned problems, in this work, we propose a typical building block to design precisely type I PSs with DR/NIR fluorescence and high photoluminescent quantum yield at aggregation by combining molecular design of aggregation-induced emission and hybrid locally and charge transfer (HLCT) theory. The synthetic small molecular PSs just produce superoxide anion without any singlet oxygen production, which is ascribed to their lower T₁ energy levels to suppress energy transfer from triplet state to oxygen. Two strategies of small molecular structural designing and polymeric nanoparticles modification are utilized to improve efficiency of type I ROS. More interestingly, original small molecular PSs is in capable to produce hydroxyl radical, once forming BSA encapsulated nanoparticles, obvious hydroxyl radical is appeared.