Halogenation-Engineered Semiconducting Polymer for Near-Infrared Fluorescence Imaging-Guided Photothermal Cancer Therapy

Near-infrared (NIR) fluorescence imaging-guided photothermal therapy (PTT) has emerged as a precise and spatiotemporally controllable strategy for tumor ablation. Organic semiconducting polymers are promising PTT agents but are often hampered by limited fluorescence emission due to the trade-off between radiative (fluorescence) and nonradiative (thermal) decay processes. To overcome this, we designed and synthesized two semiconducting polymers, PF2 and PCl2, using halogen-substituted electron donors. In PF2, fluorination at the thiophene β-position lowers the band gap and energy levels and enhances the mass extinction coefficient and fluorescence emission. PF2 nanoparticles simultaneously exhibited a remarkable fluorescence quantum yield of 2.97% and a high photothermal conversion efficiency of 69.8%, significantly outperforming chlorinated polymer PCl2. NIR fluorescence imaging-guided PTT mediated by PF2 NPs under 808 nm laser irradiation effectively inhibited the growth of 4T1 tumors in vivo. This study reveals the potential of rationally modulating halogens to develop photothermal agents with desirable integrated properties.