Orbicular‐Donor–Acceptor System in N‐doped Nanographene for Highly Efficient NIR‐II Photothermal Therapy

Developing stable and efficient photothermal agents (PTAs) for the second near‐infrared window (NIR‐II, 1 000–1700 nm) photothermal therapy (PTT) is highly desirable but remains challenging. Herein, a facile strategy to prepare NIR‐II nano‐PTA based on the ionic N‐doped nanographene hexapyrrolohexaazacoronene (HPHAC) is reported featuring a specific orbicular‐donor–acceptor (O‐D–A) structure. Oxidizing HPHAC 1 to dication 1 2+ causes a substantial decrease in its band gap, leading to a shift in absorption from the confined UV region to a broad absorption range that reaches up to 1400 nm. The dication 1 2+ exhibits global aromaticity and excellent stability. Theoretical investigation demonstrates that the strong NIR‐II absorption of 1 2+ is attributed to a distinct inner‐to‐outer intramolecular charge transfer. Encapsulating 1 2+ with amphiphilic polymers results in water‐soluble 1 2+ NPs with retained optical characteristics. The 1 2+ NPs exhibit exceptional biocompatibility, intense photoacoustic responses, and a high photothermal conversion efficiency of 72% under the 1064 nm laser irradiation, enabling efficient PTT of cancer cells. The “O‐D–A” system on HPHAC, which is created by a simple redox approach, provides a novel strategy to construct efficient NIR‐II photothermal materials through molecular engineering of nanographenes.