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 linkage of organic building blocks. Therefore, developing COFs to high-performance photocatalysts is highly applicable. Herein, with trifluoroacetic acid as the catalyst, Py-Azine-COF is constructed by aldimine condensation between 1,3,6,8-tetrakis(4-formylphenyl)pyrene and hydrazine hydrate. The highly crystalline Py-Azine-COF possesses a remarkable specific surface area of 1428 m2 g−1. Intriguingly, selective aerobic conversion is 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 for selective oxidation of organic sulfides. With the assistance of 2 mol% TEMPO, the performance of Py-Azine-COF photocatalyst is increased markedly. Gratifyingly, TEMPO, a hole mediator, enables expeditious conversions of various sulfides into sulfoxides over Py-Azine-COF photocatalyst in methanol. Generally, COFs can be customized by modulating the covalent connection of organic building blocks to meet the requirements of selective aerobic oxidations.