Precise Planar-Twisted Molecular Engineering to Construct Semiconducting Polymers with Balanced Absorption and Quantum Yield for Efficient Phototheranostics

Semiconducting polymers (SPs) have shown great feasibility as candidates for near-infrared-II (NIR-II) fluorescence imaging-navigated photothermal therapy due to their strong light-harvesting ability and flexible tunability. However, the fluorescence signal of traditional SPs tends to quench in their aggregate states owing to the strong π-π stacking, which can lead to the radiative decay pathway shutting down. To address this issue, aggregation-induced emission effect has been used as a rational tactic to boost the aggregate-state fluorescence of NIR-II emitters. In this contribution, we developed a precise molecular engineering tactic based on the block copolymerizations that integrate planar and twisted segments into one conjugated polymer backbone, providing great flexibility in tuning the photophysical properties and photothermal conversion capacity of SPs. Two monomers featured with twisted and planar architectures, respectively, were tactfully incorporated via a ternary copolymerization approach to produce a series of new SPs. The optimal copolymer (SP2) synchronously shows desirable absorption ability and good NIR-II quantum yield on the premise of maintaining typical aggregation-induced emission characteristics, resulting in balanced NIR-II fluorescence brightness and photothermal property. Water-dispersible nanoparticles fabricated from the optimal SP2 show efficient photothermal therapeutic effects both in vitro and in vivo. The in vivo investigation reveals the distinguished NIR-II fluorescence imaging performance of SP2 nanoparticles and their photothermal ablation toward tumor with prominent tumor accumulation ability and excellent biocompatibility.