Promoting a Significant Increase in the Photoluminescence Quantum Yield of Terbium(III) Complexes by Ligand...

Area of Science:

• Coordination Chemistry
• Photoluminescence Spectroscopy
• Lanthanide Complexes

Background:

• Terbium (TbIII) complexes are investigated for their luminescent properties.
• Ligand design plays a crucial role in tuning the photophysical behavior of lanthanide complexes.
• Understanding structure-property relationships is key to developing efficient luminescent materials.

Purpose of the Study:

• To synthesize and characterize two discrete mononuclear terbium complexes, [Tb(bbpen)(NO3)] (I) and [Tb(bbppn)(NO3)] (II).
• To investigate the impact of a methyl group on the ligand backbone on the structural and optical properties of TbIII complexes.
• To evaluate the photoluminescence (PL) properties, including absolute emission quantum yields and lifetimes, of the synthesized complexes.

Main Methods:

• Synthesis and characterization of mononuclear TbIII complexes using FTIR, Raman, and photoluminescence spectroscopy.
• Single-crystal X-ray diffraction for structural determination.
• Steady-state and time-resolved photoluminescence measurements at room temperature and 11 K.
• Quantum-mechanical calculations (DFT and TD-DFT) for ligand analysis.

Main Results:

• Complexes [Tb(bbpen)(NO3)] (I) and [Tb(bbppn)(NO3)] (II) were successfully synthesized and characterized.
• The methyl group in the ligand of complex II leads to distinct structural and optical properties compared to complex I.
• Complex II exhibits a significantly higher absolute emission quantum yield (67 ± 7%) than complex I (21 ± 2%) at room temperature.
• Both ligands (H2bbpen and H2bbppn) function effectively as "antennas" for TbIII sensitization.

Conclusions:

• The conformational differences in the ethylenediamine bridge, influenced by the methyl group, minimize non-radiative decay pathways in complex II.
• Ligand modification is a viable strategy to enhance the luminescence efficiency of TbIII complexes.
• Complex II demonstrates superior photoluminescence performance, making it a promising candidate for applications requiring high luminescence efficiency.