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

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(L1)]) and DO3A ([Na][Eu(L2)]) 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(L1)]) present a lower brightness than the ([Na][Eu(L2)]) counterpart because of its inner sphere water molecule coordination that quenches the emission. On the other hand, [Na][Eu(L2)] exhibits excellent spectroscopic properties with high quantum yield ϕ = 0.284, and brightness B = 10,220 M−1cm−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.

RésuméCet article décrit la synthèse et la complexation à l’europium (III) de deux ligands macrocycliques de type DTPA bis-amide ([Eu(L1)]) et DO3A ([Na][Eu(L2)]) fonctionnalisés par des groupements donneur-phenylène-ethynylène. Ces macrocycles ont été choisis en raison de leur stabilité reconnue dans les milieux biologiques afin de concevoir de nouvelles bio-sondes luminescentes pour la microscopie biphotonique. L’étude des propriétés spectroscopiques de ces deux complexes a mis en évidence l’excellent rendement quantique de luminescence, ϕ = 0,284 ainsi que la brillance B = 10 220 M−1cm−1(définie comme le produit ɛ.ϕ) accrue du composé [Na][Eu(L2)]. Cependant, sa faible section efficace d’absorption à deux photons limitera ses potentialités en microscopie non linéaire.