Sequential effects of two cations on the fluorescence emission of a coordination polymer with ZnO core in node.

Distinct changes in the fluorescence emissions of free ligand 5-(1,3-dioxo-1-benzo[de]isoquinolin-2(3)-yl)isophthalic acid (HNAPHISO) than a 2D-zinc-coordination polymer of it, caused by sequential interactions with different sets of binary cations were observed. The coordination polymer having unsymmetrical ZnO core of tetranuclear zinc-node could be dispersed in dimethylformamide without its degradation. The coordination polymer had an emission peak at 435 nm (quantum yield = 0.082) which was selectively quenched by adding Fe ions. Based on this quenching, the Fe ions in aqueous solution could be detected with a detection limit 42.57 nM. The metal ions such as Li, Na, Cd, Hg, Al did not interfere in the detection; but each of these ions together with Fe ions showed characteristic shift of the emission spectra. The HNAPHISO in dimethyl formamide was non-fluorescent, but showed emission at 452 nm upon addition of Cd or Zn ions. This new emission of HNAPHISO caused by zinc or cadmium ions was not quenched by Fe ions. Various cations had affected the emission of the HNAPHISO with Zn which was much different from the corresponding changes caused by the same ion on the emission of the coordination polymer. For example, the Mn and Zn ions together in a solution of the ligand showed a broad emission spectrum spreading over 380-450 nm, but ions Sn and Zn together had showed emission at a shorter wavelength (380 nm). These allowed to modulate the emission of the ligand by binary combination of metal ions.