Organic radicals stabilization above 300 °C in Eu-based coordination polymers for solar steam generation.

Organic radicals feature unpaired electrons, and these compounds may have applications in biomedical technology and as materials for solar energy conversion. However, unpaired electrons tend to pair up (to form chemical bonds), making radicals unstable and hampering their applications. Here we report an organic radical system that is stable even at 350 °C, surpassing the upper temperature limit (200 °C) observed for other organic radicals. The system reported herein features a sulfur-rich organic linker that facilitates the formation of the radical centers; on the solid-state level, the molecules are crystallized with Eu(III) ions to form a 3D framework featuring stacks of linker molecules. The stacking is, however, somewhat loose and allows the molecules to wiggle and transform into sulfur-stabilized radicals at higher temperatures. In addition, the resulting solid framework remains crystalline, and it is stable to water and air. Moreover, it is black and features strong broad absorption in the visible and near IR region, thereby enhancing both photothermal conversion and solar-driven water evaporation.