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.