Boosting charge separation in conjugated microporous polymers via fluorination for enhancing photocatalysis

Abstract

Conjugated microporous polymers (CMPs) have emerged as prospective heterogeneous photocatalysts for photocatalytic aerobic oxidation due to their ease of functionalization, high surface area and porosity, and tunable band gap. However, their photocatalytic efficiency was much lower than expected due to the fast charge recombination and insufficient charge separation. Herein, a fluorination strategy was developed to inhibit charge recombination and promote charge separation in CMPs by selectively employing carbazole as the donor and fluorinated precursors as the acceptor, respectively. As a result, a series of fluorinated CbzCMP-n (n = 10–12) featuring π-conjugates of the donor (D)–acceptor (A) structure is obtained, in which both their effective charge separation and transfer and broadly visible light absorbance are facilitated. The fluorinated CbzCMP-11 and CbzCMP-12 significantly enhanced the photocatalytic efficiency compared to their counterpart CbzCMP-10 free of fluorination, as demonstrated by the photocatalytic construction of benzimidazoles and oxidation of sulfide. This fluorination strategy sheds light on the promotion of better balancing of the electron and hole migration rates, the inhibition of charge recombination, and the expansion of the prospects of CMPs as metal-free photocatalysts in the conversion of various organic transformations.