Charge-Transfer Cocrystal via a Persistent Radical Cation Acceptor for Efficient Solar-Thermal Conversion.

Designing organic charge-transfer (CT) cocrystals for efficient solar-thermal conversion is a long-sought goal but remains challenging. Here we construct a unique CT cocrystal by using a persistent 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS +. ) as the electron acceptor. The strong persistency and electron affinity of ABTS +. endow a high degree of electron delocalization between ABTS +. and the 3,3',5,5'-tetramethylbenzidine donor. Together with the intrinsic long-wavelength absorption of ABTS +. , the synthesized cocrystal can effectively capture the full solar spectrum and show distinguished photothermal efficiency. Such a cocrystal is further used for solar-driven interfacial evaporation, and a high evaporation rate of 1.407 kg m -2  h -1 and a remarkable solar-to-vapor efficiency of 97.0 % have been achieved upon 1 sun irradiation. This work indicates the enormous prospects for charge transfer-based functional materials through rational radical cation engineering.