Robust Organic Radical Cations with Near-Unity Absorption across Solar Spectrum

Developing low energy-gap materials for efficient photothermal conversion provides promising candidates for solar energy utilization. Herein, we explore the feasibility of employing robust organic radical cations as near-unity solar absorbers for practical seawater evaporation. Gram-scale organic radical cations are straightforwardly synthesized through single-electron oxidation. The open-shell structure and intervalence charge transfer (IVCT) characteristics of radicals enable near-unity absorption of full solar spectral irradiance. Femtosecond transient absorption spectroscopy reveals that the IVCT electron relaxes nonradiatively in femtoseconds, with a rapid rate of 5.26 × 10<12/sup>12 s<-1/sup>. Notably, the radical cations exhibit exceptional stability, attributed to para-position protection, spin delocalization, and frontier orbitals inversion. By simply soaking cellulose paper, a highly efficient interfacial evaporation system is established. Under one sunlight irradiation, the system achieves a remarkable solar-to-vapor conversion efficiency of 110% and a high evaporation rate of 1.60 kg·m<-2/sup>·h<-1/sup>. This work opens a new avenue for applying robust radical cations as a cutting-edge candidate for photothermal materials.