Metal selection tactic in a nitronyl nitroxide biradical-3d–4f macrocycle for boosting photothermal conversion and the application of solar-driven water evaporation

Abstract

Metal–organic photothermal conversion materials are vital for the efficient utilization of renewable energy to relieve freshwater shortage. Driven by the aspiration to pursue performant photothermal conversion materials, extensive efforts have been committed to regulating the photothermal effect. Decoration of the molecular skeleton represents the traditional design idea for adjusting the photophysical features. Distinctively, here, we introduced a more easy-to-operate heterometallic selection tactic that allowed for fine adjustment of the 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 revealed that photothermal conversion efficiency follows the trend DyCo-1 (75.5%) > YbCo-2 (71.9%) > DyZn-3 (57.3%) on account of the 3d/4f metal modulation, suggesting that the Dy–Co combination achieved the optimization of photothermal performance. Furthermore, DyCo-1 was successfully applied to solar-driven water evaporation with an 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 offers a feasible heterometallic modulation strategy to elaborately design molecular photothermal agents as well as a new material selection for solar-driven water evaporation and freshwater production to alleviate water scarcity.