Highly luminescent Tb(III) macrocyclic complex based on a DO3A hosting unit and an appended carboxylated N,C-pyrazolylpyridine antenna

• A new ligand (DO3A-PyPzCOOH) for lanthanide ions is reported.
• PyPzCOOH unit acts as a binding sensitizer for Eu3+ and Tb3+ ions.
• The ligand → Ln energy transfer controls the overall efficiency of emission of Eu3+.
• The Tb complex is attractive as an efficient luminescent probe in aqueous solutions.

The synthesis of a new ligand based on a DO3A moiety (DO3A = 1,4,7,10 tetraaza cyclododecane -1,4,7-triacetic acid) as a hosting agent for the lanthanide ions and an appended chromophoric unit N,C-pyrazolylpyridine core functionalized by a carboxylic acid in the 3-position of the pyrazole ring was reported. The luminescence properties of the 1/1 Eu(III) and Tb(III) corresponding complexes were investigated in air-equilibrated water and deuterated water (Tris buffer, pH 7.4) at 298 and 77 K. High luminescence lifetime (τ = 2.30 ms), quantum yield (Φ = 45%) and efficiency for the sensitized emission (ηsens = 60%) were observed for the terbium complex. A detailed study of the steps originating from light absorption at the chromophore unit and leading to lanthanide-centred emission was reported.

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