Synthesis, crystal structures, and photophysical properties of lanthanide complexes containing pyrrole-derivatized carboxylate ligands

Two pyrrole-deriviatized carboxylic acids [L¹ = 1-methylpyrrole-2-carboxylate] and [L² = N-methyl-3-indoleglyoxylate] were used as ligands to prepare six lanthanide coordination compounds [(L ¹)₃Ln]_n (Ln = Eu, 1; Gd, 2; Tb, 3) and [(L ²)_n-Ln(NO₃)(MeOH)₂]_n (Ln = Eu, 4; Gd, 5; Tb, 6). These complexes have been synthesized and structurally characterized by single-crystal X-ray diffraction. The phosphorescence behavior of the ligands in the Gd³⁺ complexes show that modification of the ligands can tune the triplet energy levels of the ligands so that they match the ⁵D₀ energy level of Eu³⁺ and the ⁵D₄ energy level of Tb³⁺; thus, the energy transfer efficiency from antenna to Eu³⁺ and Tb³⁺ is improved, and the Eu³⁺ and Tb³⁺ emission intensity is enhanced. This concept can be applied towards improving the luminescent properties of Ln³⁺ complexes by the modification of coordinating ligands.