A highly sensitive fluorescent sensor for Cd²⁺ and Zn²⁺ based on diarylethene with a pyrene unit

A novel multifunctional diarylethene fluorescence sensor 1O containing pyrene unit was designed and synthesized. The photochromism and fluorescence photoswitching properties of this diarylethene were studied in detail by irradiation of UV/Vis lights and response of metal ions in acetonitrile solution. Diarylethene fluorescence sensor 1O has high selectivity and sensitivity for the detections of Cd²⁺ and Zn²⁺. The limit of detections (LODs) for Cd²⁺ and Zn²⁺ were determined to be 1.85 × 10^-9 mol L^-1 and 7.68 × 10^-9 mol L^-1, respectively. The binding constants (K_a) of 1O with Cd²⁺ and Zn²⁺ in acetonitrile solution were calculated to be 5.8 × 10⁴ mol^-1 L and 6.0 × 10⁴ mol^-1 L, respectively. The compound 1O responded to the metal ions (Cd²⁺/Zn²⁺) to form complexations with 1 : 1 stoichiometry which were verified by Job's plot and MS analysis, respectively. In addition, the fluorescence sensor 1O has been successfully applied to the detection of Cd²⁺ and Zn²⁺ in real water samples and processed into test strips for on-site analysis and testing.