Unveiling the potential of a covalent triazine framework based on [1]benzothieno[3,2-b][1]benzothiophene (DPhBTBT-CTF) as a metal-free heterogeneous photocatalyst

Abstract

The development of photocatalysts that are effective in different organic processes is a topic of great interest to researchers in materials chemistry. Herein, we report the design and synthesis of a new covalent triazine framework (CTF) built by acid-catalyzed trimerization of 4,4′-(benzo[b]benzo[4,5]thieno[2,3-d]thiophene-2,7-diyl)dibenzonitrile activated by microwaves that generates a new organic polymer, DPhBTBT-CTF. This CTF exhibits visible-light absorption due to the electron-donating BTBT units and the extended π-conjugated framework with the electron-acceptor triazine node and proves to be an efficient and versatile metal-free heterogeneous photocatalyst for different organic processes such as selective oxidations of both sulfides and benzyl alcohols to sulfoxides and benzaldehydes, respectively or the oxidative bromination of electron rich aromatic compounds. Moreover, two different proof of concept reactions were tested: the Diels–Alder cycloaddition and the hydroxylation of boronic acids. Heterogeneity studies confirmed that this photocatalyst can be recycled without significant loss of selectivity, and also some mechanistic tests suggested the preferred oxidation pathway.