Laser‐Induced 3D Arch‐Bridged Solar Evaporator Based on Diradical‐Featured Photothermal Polymers for Highly Efficient Seawater Desalination

Solar-driven water evaporation is a sustainable approach to addressing freshwater scarcity and environmental pollution. However, the broader application is hindered by low photothermal conversion efficiency, and poor salt-rejecting properties. Herein, we designed a novel open-shell organic radical photothermal material, PSSe-Se, based on a novel acceptor unit derived from the structural modification of benzo[1,2-c:4,5-c']bis[1,2,5]thiadiazole (BBT). The ultrastrong electron-withdrawing ability, induced by a selenium-tailoring strategy and the use of thiophene as the π-bridge, facilitates significant intramolecular charge transfer, enabling near full-spectral-range absorption. The alkyl chains grafted onto thiophene provide more intramolecular rotation space, thereby enhancing the non-radiative transition. The substitution of Se in BBT receptors and their polymerization with electron-donating selenophene groups increase the diradical character, leading to enhanced paramagnetic activity, and consequently an extremely low fluorescence quantum yield. Therefore, PSSe-Se powder achieves an impressive photothermal conversion efficiency of 32.04% under 1 sun irradiation. We developed a laser-induced 3D arch-bridged solar evaporator (LIBA-Se) for continuous solar-powered desalination. The evaporator, featuring uniformly distributed surface grooves, induces Marangoni flow, thereby effectively alleviating salt accumulation and achieving a remarkable water evaporation rate of 2.65 kg/m²·h (3.5 wt% NaCl) and 2.5 kg/m²·h (20 wt% NaCl) under 1 sun illumination. Moreover, the evaporator exhibits excellent metal chelation, outstanding acid-base resistance, and remarkable stability. Our study provides new insights into the rational design of efficient photothermal conversion materials and the development of efficient seawater desalination.