Selective binding and inverse fluorescent behavior of magnesium ion by podand possessing plural imidazo[4,5-f]-1,10-phenanthroline groups and its Ru(II) complex.

[structure: see text] Two podands, 4,4'-[(ethylenedioxy)bis(ethyleneoxy)]bis[1-(2-imidazo[4,5-f]-1,10-phenanthroline)benzene] (1) and Ru(phen)(2)(1)(PF(6))(4) (2) complex, were synthesized from 1,10-phenanthroline. The photophysical behavior and the binding ability of 1 and 2 with some alkali metal and alkaline earth cations were investigated by UV-vis and fluorescence spectrometry and (1)H NMR experiments as well as fluorescence lifetime measurements. The complex stability constants (K(S)) and Gibbs free energy changes (DeltaG degrees ) for the stoichiometric 1:1 complexation of 1 and 2 with the cations were obtained by the fluorimetric titrations. The podands 1 and 2 exhibit different fluorescent behavior in the cations examined, i.e., fluorescence quenching for 1, and fluorescence enhancement for 2. In particular, 1 showed responses specific for Mg(2+), resulting in readily distinguishable by eye.