Four new coordination polymers with 2D → 2D interpenetrating networks and fluorescence quenching response to nitrobenzene

Compound 4 shows sensitive luminescence quenching response to nitrobenzene with quenching constant of 2.46×103 M−1 and detection limit of 6.19×10–6 M, and the corresponding fluorescence quenching behavior is attributed to synergistic effects of the competitive absorption between compound 4 and nitrobenzene, Förster resonance energy transfer and photo-induced electron transfer. [Display omitted] With the growing interests in two-dimensional (2D) materials, the rational assembly of new 2D coordination frameworks with functional properties have attracted extensive attentions. Four new isomorphic compounds with 2D → 2D interpenetrating structures, [M(cppp)2]n [M = Co (1), Cu (2), Ni (3) and Zn (4); Hcppp = 1- (4-carboxylphenyl)-3-(pyrid-4-yl) pyrazole] were rationally assembled through the reactions between suitable organic ligand (Hcppp) and metal nitrates. Compounds 1–4 were completely characterized by adsorption and desorption isotherms, elemental analysis, infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy, single crystal X-ray diffraction and thermo-gravimetric analysis. The solid state fluorescence spectrum of compound 4 indicates an attractive blue luminescence behavior with a maximum emission peak at 473 nm, and the corresponding solvent-emulsions show turn-off fluorescence behavior to nitrobenzene (NB) in pure water environment. The quenching constant (KSV) and detection limit of compound 4 for electron-deficient NB reached 2.46×103 M−1 and 6.19×10–6 M, respectively. Notably, SEM and N2 adsorption-desorption isotherm indicated the block crystals of compound 4 after ultra-sonication can been effectively stripped into 2D lamellar structure, which can effectively provide recognition sites of π•••π interactions for NB. According to the experimental and theoretical simulation results, fluorescence quenching behavior of compound 4 by NB should be attributed to synergistic effects of competitive absorption between compound 4 and NB, Förster resonance energy transfer and photo-induced electron transfer. The fluorescence lifetimes of compound 4 in water and NB water dispersion indicate fluorescence sensing process was static.