Photophysical studies of highly luminescent europium(III) and terbium(III) complexes functionalized with amino and mercapto groups

This work proposes the replacement of coordinated-water molecules from the precursor complexes [Ln(aba)3(H2O)] and [Ln(tta)3(H2O)2], (Ln=Eu3+, Gd3+ or Tb3+, aba−=aminobenzoate, tta−=thenoyltrifluoroacetonate) by the ligands mercaptobenzoate (mba−), mercaptopropionate (mpa−), phenanthroline (phen), dimethylformamide (dmf) and acetoacetanilide (aaa−), leading to anionic or neutral amino (-NH2) or mercapto (-SH) functionalized-lantanides (III) complexes with reasonable emission quantum yields for potential application on fluorescence microscopy of biological moieties. The complexes photophysical properties were studied using luminescence spectroscopy and theoretical models to determine the transfer and back energy transfer rates and quantum yields, that were compared with experimental ones. The anionic complexes [Eu(tta)3(L)]− showed high quantum yield values and their sensitization efficiency are in the range of 39-81%. The overlay of the ground state geometries, obtained from the Sparkle/PM3 model, of the complexes [Eu(tta)3(aba)]−, [Eu(tta)3(mba)]− and [Eu(tta)3(mpa)]−, suggest similar coordination polyhedrons occupied by the europium(III). The highest transfer rates T→5D1,0 were obtained for the anionic complexes [Eu(tta)3(L)]− which might be a result of the low triplet level energies and RL values.