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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.
Schmittel et al. (Sat,) studied this question.