Acceptor-Modulated Excitonic Dynamics in sp² C = C Linked Isostructural Covalent Organic Frameworks Enabling Diverse...

Sp² C = C linked covalent organic frameworks (COFs) are typically synthesized via the condensation reaction of activated methyl/methylene groups with aldehyde groups, in which the activating groups are commonly nitrogen-containing cyano-moiety or aromatic heteroarenes with C = N bonds. The position of the N-moiety within the acceptor unit modulates excitonic dynamics, including charge transfer, exciton dissociation, and, in some processes, intersystem crossing from the S₁ excited state to the T₁ state, which thereby influences the photocatalytic efficiency. The synergistic optimization of these excitonic behaviors holds promise for achieving enhanced photoactivity and multifunctionality, however, it is inherently challenging. To address this challenge, in this work, three isostructural vinylene linked COFs were synthesized through the modulation of N-containing electron-withdrawing units. Theoretical calculations and photophysical characterization demonstrate that COF-3, bearing a benzonitrile moiety, exhibits the most pronounced performance in both charge transfer and exciton dissociation. Conversely, COF-1 (with phenylacetonitrile) and COF-2 (containing a triazine unit) exhibit contrasting limitations: COF-1 demonstrates the poorest charge transfer and COF-2 shows the least effective exciton dissociation. Moreover, COF-3 exhibits enhanced intersystem crossing compared to the other two COFs. These advantages facilitate the generation of O₂ ^‒∐ and ¹O₂. Consequently, COF-3 enables highly efficient photocatalysis for multiple organic transformations.