Visible Light-Driven C-3 Functionalization of Indoles over Conjugated Microporous Polymers

Abstract

Metal-free and heterogeneous organic photocatalysts provide an environmentally friendly alternative to traditional metal-based catalysts. This paper reports a series of carbazole-based conjugated microporous polymers (CMPs) with tunable redox potentials and explores their photocatalytic performance with regard to C-3 formylation and thiocyanation of indoles. Conjugated polymers were synthesized through FeCl 3 mediated Friedel–Crafts reactions, and their redox potentials were well regulated by simply altering the nature of the core (i.e., 1,4-dibenzyl, 1,3,5-tribenzyl, or 1,3,5-triazin-2,4,6-triyl). The resulting CMPs exhibited high surface areas, visible light absorptions, and tunable semiconductor-range band gaps. With the highest oxidative capability, CMP-CSU6 derived from 1,3,5-tri(9 H -carbazol-9-yl)benzene showed the highest efficiency for C-3 formylation and thiocyanation of indoles at room temperature. Notably, the as-made catalysts can be easily recovered with good retention of photocatalytic activity and reused at least five times, suggesting good recyclability. These results are significant for constructing high-performance porous polymer catalysts with tunable photoredox potentials targeting an efficient material design for catalysis.