Electronic-effect regulated covalent organic frameworks as heterogeneous photoactive catalysts

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, indicating electron-donating thiomethyl groups of PyBMT-COF are more favorable to enhance distribution of electron cloud than electron-withdrawing fluorine groups of PyDF-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, longer fluorescent lifetime and lower electrochemical impedance. [Display omitted] •Two new conjugated pyrene-based covalent organic frameworks have been prepared.•Highly selective aerobic hydroxylation of arylboronic acids proceeded in high yields and a wide substrate scope using PyBMT-COF as a photocatalyst..•Electron-donating effect of thiomethyl groups in PyBMT-COF dramatically increases the photocatalytic activity compared with PyDF-COF.