Synchronously Manipulating the D−A Interaction and Planarity in Semiconducting Polymers to Achieve 84.7% Photothermal Conversion Efficiency for NIR‐II Imaging‐Guided Tumor Therapy

Abstract Exploiting photothermal agents with second‐near‐infrared (NIR‐II, 1000−1700 nm) emission and a high photothermal conversion efficiency (PCE) is an appealing and challenging task. Herein, by simultaneously tailoring the D−A interaction and planarity in fluorophores, two donor‐acceptor (D−A) −type semiconducting polymers (SPs), T‐BTP and B‐BTP, are constructed. Compared with T‐BTP, B‐BTP shows increased intramolecular interactions and improved molecular planarity, leading to bathochromic‐shift absorption, NIR‐II emission, and high PCE. Notably, the B‐BTP NPs achieve a remarkable PCE of 84.7%, which is among the highest PCEs of SPs in NIR‐II fluorescence imaging‐guided photothermal therapy (PTT). Because of these promising features, B‐BTP NPs are successfully used in NIR‐II vascular imaging and cancer therapy. This study provides valuable guidelines for the development of high‐performance NIR‐II SPs.