D-A-D-structured boron-dipyrromethene with aggregation-induced enhanced phototherapeutic efficiency for near-infrared fluorescent and photoacoustic imaging-guided synergistic photodynamic and photothermal cancer therapy

Clinical phototheranostic agents suffer from low absorption in near-infrared（NIR） region, decreasing singlet oxygen quantum yield（1O2QY） caused by aggregation in water, and low photothermal conversion efficiency（PCE）, all of which are factors weakening their phototheranostic efficacy. Herein, we designed and synthesized a donor-acceptor-donor（D-A-D） structured boron-dipyrromethene derivative（B-2TPA） which exhibited NIR absorption and fluorescence. After being encapsulated in amphiphilic distearoyl phosphoethanolamine polyethyleneglycol 2000（DSPE-PEG-2000）, the water-soluble B-2TPA nanoparticles（NPs）had increasing1O2QY（6.7%） due to the intermolecular aggregation-induced decrease in the energy gap between singlet and triplet excited states. Moreover, the quenched fluorescence and stable twisted intramolecular charge transfer in aggregates further increased the PCE of B-2TPA NPs to 60.1%. In vitro and in vivo studies confirmed that B-2TPA NPs could be used in NIR fluorescence and photoacoustic imagingguided synergistic photodynamic and photothermal therapy in tumor treatment.