Luminescent iridium phenanthroline crown ether complex for the detection of silver(I) ions in aqueous media

The crown ether-linked iridium(III) complex [Ir(ppy)2 (di-aza-phen)]+ (1) {ppy = 2-phenylpyridine and di-aza-phen = 4,7-di(1,4-dioxa-7,13-dithia-10-azacyclopenta-dec-10-yl)-1,10-phenanthroline (7)} has been prepared. Compound 1 exhibits a notable luminescence enhancement in the presence of Ag+ in aqueous media. The analogous ruthenium(II) complex [Ru(phen)2(di-aza-phen)]2+ (4) {phen = 1,10-phenanthroline}, although equally exhibiting a luminescence enhancement in the presence of Ag+, is a far inferior sensor for Ag+ than 1. The 10 times higher luminescence enhancement (I - I0)/I0 of 1 was attributed to a dominance of the emission involving the di-aza-phen ligand that is responsible for binding to the metal ion. In contrast, the 3MLCT emission of 4 does not involve the di-aza-phen ligand but does involve the phen ligand, thus only allowing for a remote effect upon addition of Ag+ ions. While 1 is a highly selective chemosensor for Ag+ in the presence of many metal ions, there is a strong interference of Hg2+ that may restrict its practical use.