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(SO4)(DIN)(H2O)] (CP-1), [Cd(NO3)2(DIN)] (CP-2), [Mn (SO4)(DIN)(H2O)3] (CP-3), and [Co(NO3)2(DIN)2(H2O)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 7ex = 230 and 290 nm, and at a single emission wavelength of 7em = 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 (7ex = 230 nm) and imidacloprid (7ex = 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.