Precise Manipulation on Effects of Framework Microenvironment in Covalent Triazine Frameworks for Efficient Photocatalytic C3–H Thiocyanation of Indole

Abstract

Owing to their structural stability, diversity, and easy synthesis, characterisation, and modification, covalent triazine frameworks (CTFs) are promising heterogeneous photocatalysts for different types of organic transformations. Herein, we prepared CTFs modified with different chromophore groups (nitro group: CTF-1, thiadiazole group: CTF-2) by changing the building unit structure and compared their properties with an unmodified CTF (CTF-3). The introduction of chromophores resulted in bandgap narrowing and facilitated charge separation/transport and light collection, which showed that the photoelectric properties of CTFs can be regulated by tuning their framework microenvironment. The photocatalytic activity of these CTFs for the C3–H thiocyanation of indole followed the order of CTF-3 < CTF-1 (× 1.24 that of CTF-3) < CTF-2 (× 1.44 that of CTF-3) and was consistent with our expectations. Thus, this study provides a green method for the synthesis of indole sulphides (based on the conversion of catalytically prepared indole thiocyanates) and paves the way for the purposeful design of CTFs as photocatalysts for a diverse range of transformations.

Keywords: Photocatalysis, Heterogeneous catalysis, Covalent triazine frameworks, Porous materials, C-H thiocyanation