Fluorescent difluoroboron covalent organic frameworks via N, O-bidentate ligation

Abstract

The multi-dentate chelate ligands containing N and O atoms have good chelating ability to boron trifluoride and their complexes show good fluorescence properties. In this work, a fluorescent covalent organic framework (COF) with good crystallinity and porosity, 50% B-COF, was successfully synthesized by coordination of starting COFs 50% COF-OH with boron trifluoride diethyl etherate via N, O-bidentate ligation. Imine bonds are highly polarized. The coordination of nitrogen and boron changes the electron cloud distribution of imine bonds, causing the non-fluorescent 50% COF-OH to be transformed into fluorescent 50% B-COF. 50% B-COF exhibited red fluorescence under ultraviolet excitation. This work provides a new strategy for the design of fluorescent COFs.