Host-Guest Charge-Transfer Co-Crystals With Record-High Photothermal Conversion Efficiency for Solar-Driven Interfacial Water Evaporation.

Solar-driven interfacial water evaporation using photothermal conversion materials is essential to address global freshwater scarcity. Organic charge-transfer (CT) co-crystals are effective for photothermal conversion, but their efficiency is often limited by suboptimal CT interactions. Here, we developed a host-guest-enhanced CT interaction strategy in organic CT co-crystals for efficient photothermal conversion. Two co-crystals, TCNQ@An34C10 and F4TCNQ@An34C10, are prepared by employing an anthracene-containing crown ether (An34C10) as the electron donor host and two electron acceptor guests, 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), respectively. Benefiting from the superior electron affinity of F4TCNQ, F4TCNQ@An34C10 achieves a record-high photothermal conversion efficiency of 98.0% under 808 nm laser irradiation, far exceeding the 79.9% efficiency of TCNQ@An34C10. This performance disparity is attributed to the distinct intermolecular interactions within the host-guest complexes, as revealed by combined experimental and theoretical calculations. Based on the exceptional photothermal properties, a composite foam is fabricated for solar-driven interfacial water evaporation by loading F4TCNQ@An34C10 onto porous polyurethane, which achieves a high water evaporation rate of 1.343 kg m-2 h-1 and a solar-to-vapor efficiency of 91.1% under 1 sun irradiation. This work provides new avenues for developing advanced photothermal materials toward efficient solar energy utilization.