Thiocarbazone‐appended coumarin: An easily accessible ratiometric fluorescent chemosensor for multianalyte (Zn²⁺ and Cu²⁺) systems

Abstract A simple thiocarbazone‐appended coumarin derivative 1 with high selectivity as a ratiometric fluorescence sensor towards Cu²⁺ and Zn²⁺ in a semi‐aqueous solution was synthesised and characterised. Upon the addition of Cu²⁺ and Zn²⁺, the emission of 1 solution undergoes a blue and red shift to 480 and 545 nm according to the intense blue and yellow colour under a 365‐nm ultraviolet lamp, respectively. Binding was confirmed by ultraviolet‐visible absorption analysis, fluorescence measurement, mass spectrometry, proton nuclear magnetic resonance, Fourier Transform‐infrared spectroscopy and density functional theory calculation. The results show that 1 coordinated with Cu²⁺ and Zn²⁺ in different modes, resulting in different ratiometric fluorescence responses. The detection limits of the sensor 1 for Cu²⁺ and Zn²⁺ were 100.8 and 11.5 nM, respectively. The association constants (K_a) of Cu²⁺ and Zn²⁺ with 1 were determined to be 5.59 × 10⁴ and 5.08 × 10⁴ M⁻¹, respectively. Fluorescent microscopy experiments demonstrated that probe 1 has the potential to be used to monitor Zn²⁺ and Cu²⁺ in living cells.