Near‐Infrared Conjugated Macrocyclic BODIPYs for Photothermal Cancer Therapy

With this research we developed a cyclization strategy that effectively converts radiative transitions (RTs) to non-radiative transitions (NRTs) during the decay process of BODIPY-based photosensitizers. Compared to BODIPY monomers, cyclization leads to a significant decrease in the HOMO-LUMO energy gap and a significant increase in the HOMO energy. In particular, the absorption spectrum of 7a exhibits a significant redshift, with the maximum absorption wavelength reaching 794 nm. Photophysical characterization indicates that the macrocyclic BODIPY derivatives 7(a-d) exhibit a reduced RT process. While, the crystal structure and theoretical calculations suggest that the molecular ring distortion enhances the intersystem crossing (ISC) ability of the macrocyclic BODIPY derivatives 7(a-d). In addition 7a-NPs constructed using DSPE-mPEG₂₀₀₀ encapsulation exhibit excellent water solubility, stability, and photothermal conversion efficiency (44.6%). The photothermal therapeutic performance of 7a-NPs was evaluated through in vitro cell and in vivo mice experiments. The results indicated that 7a-NPs could be enriched at the tumor site and exhibited strong tumor ablation ability using near-infrared radiation. Our findings suggest that the regulation of the RT to NRT conversion using an alkali-induced cyclization reaction is a useful strategy for preparing efficient photo-thermal conversion materials based on BODIPY.