Synthesis of four coordination polymers with Zn(II), Cd(II), Mn(II), or Co(II) ions and their application for fluorescence sensing toward nitenpyram, imidacloprid, and vitamin B2

Four new Zn(II)-, Cd(II)-, Mn(II)-, and Co(II) - based 1D to 2D coordination polymers (CPs) were synthesized from metal salts and 1,4-di(1-imidazol-1-yl)naphthalene (DIN) ligand via the coordination reaction under hydrothermal conditions with quantitative yields , namely, [Zn(SO 4 )(DIN)(H 2 O)] ( CP-1 ), [Cd(NO 3 ) 2 (DIN)] ( CP-2 ), [Mn(SO 4 )(DIN)(H 2 O) 3 ] ( CP-3 ), and [Co(NO 3 ) 2 (DIN) 2 (H 2 O) 4 ] ( CP-4 ). The CPs were analyzed and characterized using FT-IR, Elemental Analysis , TGA , SC-XRD, and PXRD . CP-1 was selected as a model sensor for fluorescence detection , and the sensor exhibited high quenching rates at two excitation wavelengths of λ ex  = 230 and 290 nm, and at a single emission wavelength of λ em  = 350 nm. At these two different excitation wavelengths, CP-1 behaved differently during the sensing of pesticides, and the highest quenching rate was achieved by the sensor for nitenpyram ( λ ex  = 230 nm) and imidacloprid ( λ ex  = 290 nm). Furthermore, during the sensing of vitamins, CP-1 encountered a strong quenching effect toward vitamin B2 . During the sensing processes, the inner filter effect (for nitenpyram , imidacloprid , and vitamin B2), fluorescence resonance energy transfer (for nitenpyram, imidacloprid, and vitamin B2), and photo-induced electron transfer (for vitamin B2) were the mechanisms responsible for fluorescence quenching .