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

ABSTRACT 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/m 2 ·h (3.5 wt% NaCl) and 2.5 kg/m 2 ·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.