Low-molecular-weight organic small-molecule photothermal material for high-efficiency solar-thermal water evaporation

Organic photothermal materials have aroused more and more attentions, due to their unique merits of diverse structure, tunable property, and good biocompatibility. However, most of them suffered from complicated design and high cost in extending the molecular conjugation for long-wavelength absorption. Herein, we interestingly discovered a typical organic conjugated molecule, 4,6-di(2-thienyl)thieno[3,4-c][1,2,5]thiadiazole (T-TTD-T) with low molecular weight of only 306 g mol−1 and simple structure, to exhibit superior photothermal performance under aggregation. T-TTD-T with rigid and planar molecular skeleton was endowed with diradical feature and could aggregate closely in π-π stacking, extending the absorption to cover from 300 to 1000 nm for effective sunlight absorption and facilitating the high photothermal conversion efficiency of 65.5 % under 685 nm laser. On this basis, T-TTD-T was successfully applied in solar-driven water evaporation to obtain a considerable evaporation efficiency of 85.2 % and water evaporation rate of 1.2366 kg m−2 h−1 under 1 sunlight irradiation. This finding would light up the enthusiasm in constructing high-efficiency but simple organic small-molecule photothermal materials. [Display omitted] •A diradical-featured organic small molecule with low molecular weight is synthesized.•The close π-π stacking enables broad absorption covering from 300 to 1000 nm.•Unexpected 65.5 % ηPT for solar-driven water evaporation with high efficiency of 85.2 % under one sun is realized.