Electronic-Effect Regulated Covalent Organic Frameworks as Heterogeneous Photoactive Catalysts

Abstract

Crystalline covalent organic frameworks (COFs) materials have good performance in photocatalytic conversions due to their excellent photoelectric properties in recent years. here, two new conjugated pyrene-based covalent organic frameworks (COFs), namely PyDF-COF and PyBMT-COF, were prepared through condensation polymerization of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraaniline and 2,5-difluoroterephthalaldehyde or 2,5-Bis(methylthio)terephthalaldehyde, respectively. Highly selective aerobic hydroxylation of arylboronic acids can occur smoothly with high yields and a wide range of substrate universality. Compared with PyDF-COF, PyBMT-COF demonstrates a more efficient ability for this aerobic hydroxylation, that is because electron-donating thiomethyl groups in the linker of PyBMT-COF are more favorable to enhance distribution of electron cloud than electron-withdrawing fluorine groups in the linker of PyBMT-COF, which make the PyBMT-COF more easily afford holes and electrons (h+-e-) separation, more effectively absorb visible light, and own narrower bandgap energy, higher photocurrent response, and longer fluorescent lifetime.

Keywords: covalent organic frameworks, hydroxylation reaction, thiomethyl groups, arylboronic acids, visible light