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Photoacoustic agents have been of vital importance for improving the imaging contrast and reliability against self‐interference from endogenous substances. Herein, we synthesized a series of thiadiazoloquinoxaline (TQ)‐based semiconducting polymers (SPs) with a broad absorption covering from NIR‐I to NIR‐II regions. Among them, the excited s‐BDT‐TQE, a repeating unit of SPs, shows a large dihedral angle and narrow adiabatic energy as well as low radiative decay, attributing to its strongly electron‐deficient ester‐substituted TQ‐segment. In addition, its more vigorous molecular motions trigger a higher reorganization energy that further yields an efficient photoinduced nonradiative decay, which has been carefully examined and understood by theoretical calculation. Thus, BDT‐TQE SP‐cored nanoparticles with twisted intramolecular charge transfer (TICT) feature exhibit a high NIR‐II photothermal conversion efficiency (61.6 %) and preferable PA tracking of in situ hepatic tumor growth for more than 20 days. This study highlights a unique strategy for constructing efficient NIR‐II photoacoustic agents via TICT‐enhanced PNRD effect, advancing their applications for in vivo bioimaging. [ABSTRACT FROM AUTHOR]

It remains highly challenging to identify small molecule‐based photothermal agents with a high photothermal conversion efficiency (PTCE). Herein, we adopt a double bond‐based molecular motor concept to develop a new class of small photothermal agents to break the current design bottleneck. As the double‐bond is twisted by strong twisted intramolecular charge transfer (TICT) upon irradiation, the excited agents can deactivate non‐radiatively through the conical intersection (CI) of internal conversion, which is called photoinduced nonadiabatic decay. Such agents possess a high PTCE of 90.0 %, facilitating low‐temperature photothermal therapy in the presence of a heat shock protein 70 inhibitor. In addition, the behavior and mechanism of NIR laser‐triggered molecular motions for generating heat through the CI pathway have been further understood through theoretical and experimental evidence, providing a design principle for highly efficient photothermal and photoacoustic agents. [ABSTRACT FROM AUTHOR]