Selective oxidation of sulfides with oxygen over a pyrene covalent organic framework photocatalyst with TEMPO

Covalent organic frameworks (COFs) can be precisely modulated through the covalent connection of organic building blocks, exhibiting desired photocatalysis. Therefore, customizing COFs to develop high-performance photocatalysts is preferable. With CF3COOH as the catalyst, Py-Azine-COF is constructed by aldimine condensation between 1,3,6,8-tetrakis(4-formylphenyl)pyrene and hydrazine hydrate. The high crystalline Py-Azine-COF possesses a remarkable specific surface area of 1428 m2 g−1. Intriguingly, selective conversions are achieved over Py-Azine-COF photocatalyst with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO). Significantly, TEMPO accelerates the hole transfer and cooperates with superoxide formed from oxygen to accomplish selective oxidation of organic sulfides. With the assistance of 2 mol% TEMPO, the activity of Py-Azine-COF photocatalyst is increased markedly. Gratifyingly, TEMPO, the hole mediator, enables expeditious conversion of various sulfides into sulfoxides over Py-Azine-COF photocatalyst in protic solvent methanol. This work highlights that COFs can be customized by modulating the covalent connection of organic building blocks to meet the requirements of selective photocatalytic oxidations.