Modulation of π-Conjugation Length in Vinylene-Linked Covalent Organic Frameworks for Efficient Photocatalysis

Vinylene-linked covalent organic frameworks (COFs) have attracted widespread interest as photocatalysts, largely due to their remarkable chemical stability and extensive π-conjugation. Nevertheless, the development of innovative monomers for the construction of vinylene-linked COFs with adjustable electronic properties remains at an early stage. To tackle this issue, a tetratopic monomer incorporating a thieno[3,2-b]thiophene backbone was rationally designed and subsequently polymerized with terephthalaldehyde and 4,4′-biphenyldicarboxaldehyde, affording two vinylene-linked COFs (PTT-BDA and PTT-BPA) that exhibited high crystallinity, outstanding stability, and pronounced π-electron delocalization. More significantly, tuning the π-conjugation length within the COF frameworks enabled the optimization of their semiconducting characteristics. Owing to its extended π-conjugation, PTT-BPA exhibited excellent semiconducting properties, which endowed it with outstanding photocatalytic activity. This study not only expands the library of vinylene-linked COFs but also introduces a straightforward strategy to modulate their semiconducting properties by adjusting the π-conjugation length within the framework structure.