Rational Synthesis of Extended π-Conjugated Covalent Organic Frameworks for Enhanced Photocatalytic Uranium(VI) Removal.

Atom-level control of π-conjugations in covalent organic frameworks (COFs) facilitates deep exploration of the relationship between electron-transport properties and photocatalysis, which is particularly important for improving photocatalytic performance. Herein, we present a comprehensive strategy for the synthesis of extended π-conjugated COFs via a one-pot tandem Scholl cyclization-dehydrogenation reaction. The extended π-conjugated COFs are constructed by planar covalent bonds, in which imine linkers are converted to imine-cyclized counterparts, resulting in all chemical bonds conjugatively connected throughout the framework. Subsequently, benzene units are substituted with naphthalene units to yield an even more highly extended π-conjugated framework. These approaches ensure that delocalized electrons efficiently transport across the COF framework with extended π-conjugation, resulting in extended-range light absorption, improved electron-hole separation, and more efficient charge-carrier utilization under visible-light irradiation. Notably, the extended π-conjugated COFs exhibit remarkable photocatalytic performance in uranium(VI) removal from contaminated water sources, surpassing the performance of electron-deficient p-π-conjugated counterparts. These findings demonstrate a new general design strategy for the synthesis of highly-conjugated COF photocatalysts. The strategy is expected to provide new insights into the rational design of high-performance COFs for applications in photocatalysis, including water-source decontamination and potentially numerous other applications.