Photochromic Donor–Acceptor Naphthalenediimides Enabling Near‐Infrared Photothermal Conversion for Seawater Desalination

ABSTRACT Photochromic donor–acceptor molecules that produce near‐infrared (NIR) absorption upon light activation offer promising platforms for organic photothermal materials. Here, neutral naphthalene diimide (NDI) derivatives with tertiary amine substituents demonstrate efficient photothermal conversion through photochromism‐induced radical formation. UV irradiation initiates intermolecular electron transfer from the electron‐donating amine groups to the electron‐deficient NDI core, generating stable radical species with strong NIR absorption. These photoactivated states enable rapid photothermal heating under 850 nm light with efficiencies reaching up to 24.5%. When integrated into a floating evaporation platform, the optimized compound achieves a water evaporation rate of 0.98 kg m − 2 h − 1 and an energy conversion efficiency of 65.5% under 1 sun illumination. These findings highlight the potential of photochromic NDI donor–acceptor systems as adjustable organic photothermal materials for solar‐driven water purification.