Mechanochemistry toward Organic "Salt" via Integer‐Charge‐Transfer Cocrystal Strategy for Rapid, Efficient, and Scalable Near‐Infrared Photothermal Conversion.

Inspired by the concept of ionic charge‐transfer complexes for the Mott insulator, integer‐charge‐transfer (integer‐CT) cocrystals are designed for NIR photo‐thermal conversion (PTC). With amino‐styryl‐pyridinium dyes and F4TCNQ (7,7',8,8'‐Tetracyano‐2,3,5,6‐tetrafluoroquinodimethane) serving as donor/acceptor (D/A) units, integer‐CT cocrystals, including amorphous stacking "salt" and segregated stacking "ionic crystal", are synthesized by mechanochemistry and solution method, respectively. Surprisingly, the integer‐CT cocrystals are self‐assembled only through multiple D−A hydrogen bonds (C−H⋅⋅⋅X (X=N, F)). Strong charge‐transfer interactions in cocrystals contribute to the strong light‐harvesting ability at 200–1500 nm. Under 808 nm laser illumination, both the "salt" and "ionic crystal" display excellent PTC efficiency beneficial from ultrafast (∼2 ps) nonradiative decay of excited states. Thus integer‐CT cocrystals are potential candidates for rapid, efficient, and scalable PTC platforms. Especially amorphous "salt" with good photo/thermal stability is highly desirable in practical large‐scale solar‐harvesting/conversion applications in water environment. This work verifies the validity of the integer‐CT cocrystal strategy, and charts a promising path to synthesize amorphous PTC materials by mechanochemical method in one‐step. [ABSTRACT FROM AUTHOR]