Distinct Ligand- and Metal-Centered Phosphorescence in a Terbium Carbazolyl Complex

Area of Science:

• Organometallic Chemistry
• Lanthanide Chemistry
• Photophysics

Background:

• Lanthanide complexes are crucial in materials science due to their unique luminescent properties.
• Cyclooctatetraene (COT) ligands offer versatile coordination environments for lanthanides.
• Carbazolide ligands provide a robust scaffold for stabilizing lanthanide complexes.

Purpose of the Study:

• To synthesize novel carbazolide complexes of lanthanum (La) and terbium (Tb) with cyclooctatetraenediide (COT) and THF coligands.
• To investigate the luminescence properties of these synthesized lanthanide complexes.
• To explore the temperature-dependent phosphorescence and excitation mechanisms.

Main Methods:

• Synthesis of carbazolide complexes via salt metathesis reactions.
• Characterization of mononuclear and dinuclear complexes.
• Investigation of luminescence spectroscopy at cryogenic temperatures.
• Theoretical calculations using TD-DFT (Time-Dependent Density-Functional Theory).

Main Results:

• Successfully synthesized [(dtbpCbz)LnCOT(thf)n] (n=2 for La, n=1 for Tb) and dinuclear complexes.
• Observed strongly temperature-dependent phosphorescence at cryogenic temperatures.
• Terbium complexes exhibited characteristic sharp emissions (480-700 nm) upon 370 nm excitation.
• Broad emission was induced in Tb complexes at lower excitation energies, and similar phosphorescence was observed for La complexes.

Conclusions:

• The synthesized carbazolide complexes of La and Tb display interesting photoluminescent properties.
• The observed broad emission in both La and Tb complexes suggests intra- or inter-ligand excitation.
• TD-DFT computations support the proposed excitation mechanisms, highlighting the role of the ligand framework in the photophysics.