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 (1O2 QY) 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 increasing 1O2 QY (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 imaging-guided synergistic photodynamic and photothermal therapy in tumor treatment.