Metal Selection Tactic in Nitronyl Nitroxide Biradical-3d-4f Macrocycle for Boosting Photothermal Conversion and Application of Solar-Driven Water Evaporation

Abstract

Metal-organic photothermal conversion materials is vital for efficient utilization of renewable energy to relieve freshwater shortage. Driven by the aspiration to pursue performant photothermal conversion materials, extensive efforts are committed to regulating the photothermal effect. Decoration of the molecular skeleton represents the traditional design idea for adjusting the photophysical features. Distinctively, here, we introduce a more easy-to-operate heterometallic selection tactic that allows for fine adjustment of photothermal conversion ability as exemplified by a series of nitronyl nitroxide biradical-based 3d-4f macrocycles, namely DyCo-1, YbCo-2, DyZn-3 and GdCo-4. The comparative investigation of DyCo-1/YbCo-2 and DyCo-1/DyZn-3 reveals that photothermal conversion efficiency follows the trend of DyCo-1 (75.5 %) > YbCo-2 (71.9 %) > DyZn-3 (57.3 %) on account of 3d/4f metal modulation, suggesting Dy-Co combination achieves the optimization of photothermal performance. Furthermore, DyCo-1 is successfully applied to solar-driven water evaporation with efficiency of 53.1 %. To the best of our knowledge, macrocyclic compounds 1-3 represent the first example of nitronyl nitroxide-3d-4f photothermal materials. The work not only offers a feasible heterometallic modulation strategy to elaborately design molecular photothermal agents, but also a new material selection for solar-driven water evaporation and freshwater production with the intention of alleviating water scarcity.