D–A polymers for fluorescence/photoacoustic imaging and characterization of their photothermal properties

NIR-II fluorescence imaging has great potential in diagnosis, but the quantum efficiency of contrast agents is an urgent problem to be solved. We synthesized two new multifunctional polymers, P-TT and P-DPP, with a tetrahedral C (sp3) and branched alkyl chains in the main chain, which were beneficial to obtain high quantum efficiency. P-TT and P-DPP showed absorption peaks of 686 nm and 763 nm, respectively, and fluorescence emission peaks of 1071 nm and 1066 nm, respectively. The photothermal effect of P-DPP can reach 52 °C, and the quantum yield reaches 1.5%, which was three times higher than that of nanotube fluorophores (quantum yield 0.4%). P-DPP is used for stable fluorescence imaging of blood vessels and photoacoustic imaging of nude mice, and successfully applied to phototherapy of nude mouse tumours.