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

Two podands, 4,4'-[(ethylenedioxy)bis(ethyleneoxy)]bis[1-(2-imidazo[4,5-f]-1,10-phenanthroline)-benzene] (1) and [Ru(phen)(2)](2)(1)(PF6)(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 H-1 NMR experiments as well as fluorescence lifetime measurements. The complex stability constants (K-S) and Gibbs free energy changes (DeltaGdegrees) 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, I showed responses specific for Mg2+, resulting in readily distinguishable by eye.