Abstract: Photodynamic therapy (PDT) is limited by its dependence on oxygen and insufficient tissue penetration depth. To address these issues, this study developed a type Ⅰ photosensitizer, DHSTPA, featuring aggregation-induced emission (AIE) characteristics based on a donor-π-bridge-acceptor (D-π-A) structure, along with its corresponding nanoparticles (DHSTPA NPs). These nanoparticles exhibit near-infrared absorption and second near-infrared (NIR-II) fluorescence emission, and efficiently generate superoxide anions and hydroxyl radicals upon 660 nm light irradiation. Both in vitro and in vivo experiments confirmed that DHSTPA NPs effectively kill breast cancer cells and inhibit tumor growth without observable systemic toxicity. In summary, DHSTPA NPs represent a potential photosensitizing system with NIR-Ⅱ emission, high type Ⅰ PDT activity, and favorable biosafety, offering a new strategy for breast cancer PDT.