Designed synthesis of an sp2 carbon-conjugated fluorescent covalent organic framework for selective detection of Fe3+

Abstract

A new fully conjugated covalent organic framework material (COF_{TFPPy–ThDAN}) has been synthesized via the Knoevenagel condensation reaction using 1,3,6,8-tetra(4-formylphenyl)pyrene (TFPPy) as the chromogenic unit and 2,2′-([2,2′-bithiophene]-5,5′-diyl)diacetonitrile (ThDAN) as the linker. The COF_{TFPPy–ThDAN} has been successfully prepared under the optimized conditions and showed excellent crystallinity and chemical stability. Especially, it was able to maintain its crystallinity even when immersed under harsh conditions such as HCl (3 M) and NaOH (3 M). Meanwhile, COF_{TFPPy–ThDAN} exhibited good fluorescence properties, which could remain relatively stable under different pH conditions. Moreover, COF_{TFPPy–ThDAN} was further employed for the detection of Fe³⁺ with high sensitivity and selectivity with a limit of detection (LOD) of 1.26 μM. COF_{TFPPy–ThDAN} with high stability and fluorescence is a promising material for chemical sensing.