Intermolecular interactions as actors in energy-transfer processes in lanthanide complexes with 2,2'-bipyridine

Area of Science:

• Inorganic Chemistry
• Materials Science
• Photochemistry

Background:

• Lanthanide complexes are crucial for luminescence applications.
• Understanding ligand-to-metal energy transfer is key to optimizing their performance.
• Molecular structure and crystal packing significantly influence photophysical properties.

Purpose of the Study:

• To synthesize and characterize lanthanide complexes with varying coordination spheres.
• To investigate the relationship between molecular geometry, crystal packing, and energy transfer efficiency.
• To elucidate the mechanisms behind enhanced luminescence in these complexes.

Main Methods:

• Synthesis of lanthanide complexes with 2,2'-bipyridine (bpy), chloride, and water ligands.
• Structural analysis using X-ray crystallography to determine molecular geometry and crystal packing.
• Photoluminescence spectroscopy to assess energy transfer efficiency.
• Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) calculations.

Main Results:

• Synthesized diverse lanthanide complexes with tunable coordination environments.
• Observed unique bpy ligand bending due to intermolecular interactions (Cl...pi, pi-stacking).
• Identified classical ligand-to-metal charge transfer (LMCT) and a novel stacking-induced charge transfer (SICT) state.
• Demonstrated that inner-sphere water molecules, through H-bonding with chloride, reduce luminescence quenching.
• Achieved a 37% quantum yield for a terbium complex, highlighting efficient near-UV to green light conversion.

Conclusions:

• Molecular geometry and crystal packing are critical determinants of energy transfer efficiency in lanthanide complexes.
• The interplay of LMCT, SICT, and hydrogen bonding significantly enhances luminescence.
• These findings provide a pathway for designing highly luminescent lanthanide materials.