Fluorescent Chemosensors for Heavy Metal Ions Based on Bis(terpyridyl) Ruthenium(II) Complexes Containing Aza-Oxa and Polyaza Macrocycles

摘要

Reactions of 4'-[4-(bromomethyl)phenylj-2,2'6',2"terpyri-dine with 4,10-diaza-15-crown-5 and 1-aza-12-crown-4 in dichioromethane yielded the ligands L~1 and L~3, respectively. Reaction of an excess of 4'-(4-(bromomethyl)phenyl]-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-pentaazacyclopentadecane afforded L~4. Reac-tions of L~1, L~3, and L~4 with Ru(mtpy)C1_3 (mtpy =4'-methyl-2,2':6',2"-terpyridine) in methanol yielded the metallo re-ceptors [Ru(L~1)(mtpy)J[PF_6]_2, [Ru(L~3)(mtpy)] [PF_6]_2, and (Ru(L~4)(mtpy)](PF_6]_2 after precipitation with ammonium hexafluorophosphate and column chromatography. On treat-ing L~3 with RuCl_3, the homoleptic ruthenium complex [Ru(L~3)_2][PF_6]_2 was obtained. The synthesized metallo recep-tors contain oxa-aza crown or polyazacycloalkane moieties as recognition sites and [Ru(tpy)_2]~(2+) cores as the signal-gen-erating centre. The electronic spectra 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 intenseligand-centred transitions in the UV region. One of the most interesting aspects of these ruthenium complexes is their multicomponent nature, as they contain both coordination sites and fluorescent Ru(tpy)_2~(2+) cores. The cations [Ru(L~1)(mtpy)]~(2+), [Ru(L~3)(mtpy)]~(2+), and IRu(L~3)_2]~(2+) display an emission maximum at ca. 650 nm, the intensity of which is pH dependent, showing an enhancement upon protonation. The metallo receptor [Ru(L~1)(mtpy)]~(2+) selectively senses Hg~(2+) in preference to Cu~(2+), Cd~(2+), and Pb~(2+). The emission intensity vs. pH curve for [Ru(L~2)(mtpy)]~(2+) in the presence of Cu~(2+) and Hg~(2+) ions is close to that of the free receptor, but the presence of Cd~(2+) or Pb~(2+) enhances the emission intensity in the range pH 4-6. For the [Ru(L~3)_2]~(2+) complex, Cd~(2+), Pb~(2+), and Hg~(2+) 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 do-main.