Side Chain Programming Synchronously Enhances the Photothermal Conversion Efficiency and Photodynamic Activity of A–D–A Photosensitizers

Synchronously improving the photothermal conversion efficiency and photodynamic activity of organic small molecule photosensitizers is crucial for their further wide application in cancer treatment. Recently, the emerging A–D–A photosensitizer-based phototherapy systems have attracted great interest due to their plentiful inherent merits. Herein, we propose a design strategy for A–D–A photosensitizers with synchronously enhanced photothermal conversion and reactive oxygen species (ROS) generation efficiencies. Side chain programming is carried out to design three A–D–A photosensitizers (IDT-H, IDT-Br, IDT-I) containing hexyl, bromohexyl, and iodohexyl side chains, respectively. Theoretical calculations confirm that a bulky iodine atom could weaken the intermolecular π–π stacking and enhance spin–orbit coupling constants of IDT-I. These molecular mechanisms enable IDT-I nanoparticles (NPs) to exhibit 2.4-fold and 1.7-fold higher ROS generation efficiency than that of IDT-H NPs and IDT-Br NPs, respectively, as well as the highest photothermal conversion efficiency. Both the experimental results in vitro and in vivo verify that IDT-I NPs are perfectly qualified for the mission of photothermal and photodynamic synergistic therapy. Therefore, in this contribution, we provide a promising perspective for the design of A–D–A photosensitizers with simultaneously improved photothermal and photodynamic therapy ability.