The heterostructurally mixed-linkage covalent organic frameworks for different fluorescence responses to alkaloids

Overdose of alkaloid drugs often causes significant damage to the human body. However, the researches about detecting alkaloids are rare and thus, it is urgent to develop a facile method to detect alkaloids. Here, four COFs TbAzo, HTbAzo, DHTbAzo and TpAzo with different ratios of β-ketoenamine/imine are synthesized When the ratio of β-ketoenamine/imine is 1/2, HTbAzo shows unique photoluminescence behavior, and the fluorescence emission is much higher than the other three COFs in water. HTbAzo shows different fluorescence responses to isoniazid (ratiometric) and colchicine (turn-off) with very low detection limits (12.60 μM for isoniazid and 1.03 nM for colchicine). HTbAzo was also applied in fluorescence sensing of isoniazid and colchicine in human serum, and the detection limits of isoniazid and colchicine were calculated to be 71.5 μM and 4.64 μM in the low concentration range, respectively. In addition, HTbAzo was also used to monitor pH (turn-on) in water with excellent linear relationship in the range of pH= 4.00–12.00 and a very low detection limit of 0.02. This work provides a new idea for improving the luminescence performance of COFs, and the different fluorescence responses of HTbAzo to alkaloids and pH make it a multifunctional sensor applied in real life.