Water-stable perylene diimide radical anions in a metal–organic framework for efficient solar-thermal conversion and steam generation

Abstract

Perylene diimide (PDI) radical anions (RAs) exhibit strong NIR-absorption and excellent photothermal conversion efficiency (PCE), making them promising candidates for advanced photothermal materials. However, their practical applications are hindered by radical quenching upon exposure to oxygen and water. Herein, we construct a high-coordination UiO-type metal–organic framework (MOF) with PDI as a ligand (UiO-PDI) whose micro-mesoporosity allows for the uptake of long alkyl amines as electron donors. Upon blue light irradiation, efficient photo-induced electron transfer (PET) occurs, forming PDI RAs and amine radical cations. Amines with long alkyl chains ensure a high in situ yield of PDI RAs due to their stable adsorption within the MOF pores and also avoid oxygen and water infiltration due to their high-boiling temperature and strong hydrophobicity. Thanks to the dense packing of PDI RAs, UiO-PDI˙⁻ displays the highest PCE of 68.1% amongst PDI RA-based materials, along with stability in air for 25 days, at 150 °C for 6 h, and in water for 6 h, respectively. An interfacial evaporation system is established from a UiO-PDI˙⁻-loaded polyurethane foam, which provides a high solar-energy-to-vapor efficiency of 99.0% and a water evaporation rate of 1.44 kg m⁻² h⁻¹ under 1 sun irradiation. The present work highlights the value of rational framework design and paves the way towards further applications of radical-based materials.