Photochromic Donor-Acceptor Naphthalenediimides Enabling Near-Infrared Photothermal Conversion for Seawater...

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.