Thienothiophene-based covalent organic frameworks for visible light-triggered oxidation of sulfides to sulfoxides

Abstract

The performance of covalent organic frameworks (COFs) as photocatalysts, grounded on light absorption and optoelectronic properties, can be precisely regulated by the building blocks. Thienothiophene is an electron-rich building block of choice for the construction of COFs. Herein, two thienothiophene-based COFs are constructed by the condensation of thieno[3,2-b]thiophene-2,5-dicarbaldehyde (TT) with 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT), respectively, affording TT-TAPB-COF and TT-TAPT-COF of high crystallinity as confirmed by powder X-ray diffraction and transmission electron microscopy. Compared to TT-TAPB-COF, TT-TAPT-COF delivers more effective light-triggered charge separation and migration because of the electron-deficient yet planar triazine in TAPT. As such, TT-TAPT-COF exhibits better performance than TT-TAPB-COF for the visible light-triggered oxidation of organic sulfides with molecular oxygen. Besides, blue light-triggered oxidation of many organic sulfides over the TT-TAPT-COF photocatalyst produces the corresponding sulfoxides with excellent conversions and selectivities. The exceptional stability of the TT-TAPT-COF photocatalyst is demonstrated by recycling experiments. Substantially, the reaction mechanism is investigated by quenching experiments and spectroscopic studies. This work provides insight into the rational design of COFs by configuring the electron donor–acceptor for the precise application in photocatalysis.