A Bithiophene-based Ratiometric Fluorescent Sensor for Sensing Cd²⁺

A novel bithiophene-naphthalene based ratiometric fluorescent chemosensor SS ((2E,2′E)-2,2′-([2,2′-bithiophene]-5,5′-diylbis(methanylylidene)) bis(N-(naphthalen-1-yl) hydrazine-1-carbothioamide)) for detecting Cd²⁺ was prepared. SS can detect Cd²⁺ by a ratiometric fluorescent response with red-shifted emission from 500 to 540 nm. The binding ratio of SS and Cd²⁺ was determined to be a 1 : 1 stoichiometry via Job plot. The detection limit was found to be 4.41 μM. The association constant (K) was calculated as 3.00×10² M⁻¹. Sensor SS was successfully applied in real water samples and fluorescent test kits for analysis of Cd²⁺. The sensing process of SS towards Cd²⁺ was illustrated by fluorescent, UV-vis and NMR spectroscopy, ESI-MS (electrospray ionization-mass spectrometry), FT-IR (Fourier transform-Infrared spectroscopy) and calculations.