π-plane size-dependent photocatalytic activity of radical-doped diimide covalent organic frameworks

Abstract

Rylene diimides (RDIs) are a type of electron-deficient organic dye exhibiting strong visible light absorption capabilities and photochemical properties that depend on the size of their π-conjugated plane. They are versatile organic monomers used for constructing covalent organic frameworks (COFs) and for investigating structure–property relationships in organic synthesis. In this study, three diimide-based COFs, PDI-COF, NDI-COF, and PBI-COF, with successively larger π-plane sizes, were constructed through condensation of 4,4′,4″-(pyridine-2,4,6-triyl)trianiline (PTT) with pyromellitic dianhydride (PDA), 1,4,5,8-naphthalenetetracarboxylic dianhydride (NDA), or 3,4,9,10-perylenetetracarboxylic dianhydride (PTA), respectively. The obtained COFs present not only well-defined crystallinity but also reactive organic radicals under ambient conditions. Upon exposure to light, all three COFs efficiently produce superoxide radical anions that promote the photocatalytic selective C–C and C–P coupling of tetrahydroisoquinoline. Combined experimental and theoretical studies demonstrated that the obtained COFs displayed prominent π-plane size-dependent photocatalytic activity in the order PBI-COF > NDI-COF > PDI-COF, consistent with the decreasing size of their electron-deficient π-conjugated planes.