Sensitization of Eu(III) luminescence by donor-phenylethynyl-functionalized DTPA and DO3A macrocycles

Abstract

The synthesis and complexation to Eu(III) of two macrocyclic ligands functionalized donor-phenylethynyl-moieties as sensitizer is presented. The two ligands based on DTPA bis-amide ( [Eu(L 1 )] ) and DO3A ( [Na][Eu(L 2 )] ) have been chosen because of their increased stability in water for potential applications as luminescent bioprobes for one- or two-photon excited scanning microscopy. The DTPA and DO3A ligands possess oxygen or sulfur donor atoms, respectively, connected to a triethyleneglycol (PEG) chain to ensure the water solubility. The optical properties were studied and reveal that ( [Eu(L 1 )] ) present a lower brightness than the ( [Na][Eu(L 2 )] ) counterpart because of its inner sphere water molecule coordination that quenches the emission. On the other hand, [Na][Eu(L 2 )] exhibits excellent spectroscopic properties with high quantum yield ϕ = 0.284, and brightness B = 10,220 M −1 cm −1 (defined as ɛ.ϕ). Unfortunately, the two-photon cross-section of this last complex was measured to be only 4 GM limiting its potential applications to linear microscopy.