A luminescent Eu coordination polymer with near-visible excitation for sensing and its homologues constructed from 1,4-benzenedicarboxylate and 1H-imidazo[4,5-f][1,10]-phenanthroline

A Eu-coordination polymer and its homologues, namely, five lanthanide coordination polymers (Ln-CPs), [Ln(BDC)(1.5)(IP)(H2O)]center dot nH(2)O (Ln = Sm 1, Eu 2, Gd 3, Tb 4, Dy 5), were constructed from 1,4-benzenedicarboxylate (BDC) and 1H-imidazo[4,5-f][1,10]-phenanthroline (IP). They feature 2D network structures with LnO(6)N(2) units by bridging BDC ligands, while the IP molecules as terminal ligands are coordinated to the Ln(iii) ions in bidentate chelating mode. The luminescence of these compounds was recorded. Eu-CP has several distinct advantages including a broad excitation band (315 nm < lambda(ex) < 410 nm) with a maximum excitation wavelength of up to 375 nm, visible red emission, and a good aqueous stability in a wide pH range of 4-10. Using Eu-CP as a chemical sensor, high luminescence sensing for emodin in aqueous medium was realized at excitation of 375 nm. Remarkably, when excited with 400 nm visible light, Eu-CP also exhibited a similar luminescence sensing capacity. UV-vis absorption spectral studies and density functional theory (DFT) calculations were performed to elucidate the possible mechanism of luminescence quenching of Eu-CP by emodin. Similarly, the detection of common ions (Fe3+, Ag+, Cr2O72-/CrO42-, MnO4-) was also realized under near-visible light of 375 or 400 nm. The experimental results prove that Eu-CP is an excellent luminescent compound, as its excitation wavelength can be adjusted to the near-visible range (350 nm < lambda(ex) < 410 nm), and strong luminescence and luminescence sensing for analytes can be achieved.