Biradical‐Featured Stable Organic‐Small‐Molecule Photothermal Materials for Highly Efficient Solar‐Driven Water Evaporation

With recent progress in photothermal materials, organic small molecules featured with flexibility, diverse structures, and tunable properties exhibit unique advantages but have been rarely applied in solar-driven water evaporation owing to limited sunlight absorption resulting in low solar-thermal conversion. Herein, a stable croconium derivative, named CR-TPE-T, is designed to exhibit the unique biradical property and strong π-π stacking in the solid state, which facilitate not only a broad absorption spectrum from 300 to 1600 nm for effective sunlight harvesting, but also highly efficient photothermal conversion by boosting nonradiative decay. The photothermal efficiency is evaluated to be 72.7% under 808 nm laser irradiation. Based on this, an interfacial-heating evaporation system based on CR-TPE-T is established successfully, using which a high solar-energy-to-vapor efficiency of 87.2% and water evaporation rate of 1.272 kg m-2 h-1 under 1 sun irradiation are obtained, thus making an important step toward the application of organic-small-molecule photothermal materials in solar energy utilization.