Design, Synthesis and Crystal Structure of a Novel Fluorescence Probe for Zn²⁺ Based on Pyrano[3,2-c] Carbazole

Zinc is a trace element, which plays an important role in many biological processes. The deficiency of zinc will lead to many diseases. Thus, it is of great significance to develop fast and efficient quantitative detection technology for zinc ions. In this study, a novel fluorescence probe FP2 was designed for Zn²⁺ quantification based on pyrano[3,2-c] carbazole. The structure of FP2 was characterized by ¹HNMR, ¹³CNMR, HRMS, and X-ray diffraction. In the HEPES buffer solution, FP2 is responsive to Zn²⁺ and greatly enhanced. The pH value and reaction time were investigated, and the optimum reaction conditions were determined as follows: the pH was 7~9 and the reaction time was longer than 24 min. Under the optimized conditions, the concentration of FP2 and Zn²⁺ showed a good linear relationship in the range of 0~10 μM, and the LOD was 0.0065 μmol/L. In addition, through the ¹H NMR titration experiment, density functional theory calculation, and the job plot of FP2 with Zn²⁺ in the HEPES buffer solution, the binding mode of FP2 and Zn²⁺ was explained. Finally, the method of flame atomic absorption spectrometry (FAAS) and FP2 were used to detect the content of Zn²⁺ in the water extract of tea. The results showed that the FP2 method is more accurate than the FAAS method, which shows that the method described in this work could be used to detect the content of Zn²⁺ in practical samples and verify the practicability of this method.