StableRadical Cation-Containing Covalent OrganicFrameworks Exhibiting Remarkable Structure-Enhanced Photothermal Conversion

The production of a radical cation-containing covalent organic framework (COF) has been accomplished by sequential in situ reactions, quaternization, and one-electron reduction of the 2,2′-bipyridine-based COFs. The acid-catalyzed COF formation enables the cis configuration of 2,2′-bipyridyl moieties in the structure, of which the stability arises from the eclipsed stacking of the two-dimensional layered structure. The postfunctionalization generates cyclic alkylated diquats as the sole products from the controlled quaternization. The reduction of diquat cations on the COF skeletons results in a large number of radical cations, which delocalize and uniaxially stack on top of one another by virtue of interlayered π-electronic couplings. The absorption of the near-infrared (NIR) region exhibited by the cationic radical COF is remarkably high owing to the intercharge transfer across the π-coupling interlayers. Also, the long-range array of extended and planar frameworks in such a COF leads to the extra stabi...