Preparation of two new polyimide bond linked porous covalent organic frameworks and their fluorescence sensing application for sensitive and selective determination of Fe3+

Two new polyimide based porous covalent organic frameworks (PI-COF 201 and PI-COF 202) were synthesized in high yields by directly heating mixtures of melamine and pyromellitic dianhydride and naphthalenetetracarboxylic dianhydride in a N-2 atmosphere, respectively. Their structures and properties were characterized using elemental analysis, Fourier transform infrared spectra, X-ray photoelectron spectroscopy, X-ray powder diffraction, N-2 adsorption-desorption and scanning electron microscopy and their fluorescence properties were studied in detail. These two COFs emitted strong fluorescence in appropriate solvents that originated from the pi* -> n transition caused by the high electrodelocalization and inherently rigid structure of the COF materials. The strong quenching effects of Fe3+ on the fluorescence of the COFs allowed selective chemosensing for Fe3+.