Fluorescent chemosensors for heavy metal ions based on bis(terpyridyl) ruthenium(II) complexes containing aza-oxa and polyaza macrocycles

Reactions of 4'-[4-(bromomethyl)phenyl]-2,2':6',2''-terpyridine with 4,10-d iaza-15-crown-5 and 1-aza-12-crown-4 in dichloromethane yielded the ligands L-1 and L-3, respectively. Reaction of an excess of 4'-[4-(bromomethyl)phe nyl]2,2':6',2''-terpyridine with 4, 10-diaza-15-crown-5 yielded L-2, while treatment of the same terpyridine ligand with 1,4,7,10,13-pentaazacyclopent adecane afforded L-4. Reactions of L-1, L-3, and L-4 With Ru(mtpy)Cl-3 (mtp y = 4'-methyl-2,2':6',2'' -terpyridine) in methanol yielded the metallo rec eptors [Ru(L-1)(mtpy)][PF6](2), [Ru(L-3)(mtpy)][PF6](2), and [Ru(L-4)(mtpy) ][PF6](2) after precipitation with ammonium hexafluorophosphate and column chromatography. On treating L-3 with RuCl3, the homoleptic ruthenium comple x [Ru(L-3)(2)][PF6](2) was obtained. The synthesized metallo receptors cont ain oxa-aza crown or polyazacycloalkane moieties as recognition sites and [ Ru(tpy)(2)](2+) cores as the signal-generating centre. The electronic spect ra of the complexes are as expected for an Ru(tpy)(2)(2+) chromophore, with the main Ru[d(pi)] --> tpy(pi*) MLCT transition at ca. 484 nm and intense ligand-centred transitions in the UV region. One of the most interesting as pects of these ruthenium complexes is their multicomponent nature, as they contain both coordination sites and fluorescent Ru(tpy)(2)(2+) cores. The c ations [Ru(L-1)(mtpy)](2+), [Ru(L-3)(mtpy)](2+), and [Ru(L-3)(2)](2+) displ ay an emission maximum at ca. 650 nm, the intensity of which is pH dependen t, showing an enhancement upon protonation. The metallo receptor [Ru(L-1)(m tpy)](2+) selectively senses Hg2+ in preference to Cu2+, Cd2+, and Pb2+. Th e emission intensity vs. pH curve for [Ru(L-2)(mtpy)](2+) in the presence o f Cu2+ and Hg2+ ions is close to that of the free receptor, but the presenc e of Cd2+ or Pb2+ enhances the emission intensity in the range pH 4-6. For the [Ru(L-3)(2)](2+) complex, Cd2+, Pb2+, and Hg2+ induce an enhancement of the fluorescence of the Ru(tpy)(2)(2+) core in the range pH 3.5-7.5. These results are compared with those obtained for the metallo receptor [Ru(L-4) (mtpy)](2+) containing a polyazacycloalkane moiety as the binding domain.