Heteroleptic [Cr^IIIN₆] Chromophores as Partners for Lanthanide-Based Light Conversion in d-f Molecular Complexes.

Area of Science:

• Coordination Chemistry
• Materials Science
• Photophysics

Background:

• Chromophores based on chromium complexes with chelating ligands are crucial for developing advanced materials.
• Lanthanide ions are essential for luminescence applications, particularly in energy transfer processes.
• Bridging ligands play a key role in constructing heterometallic complexes with tailored properties.

Purpose of the Study:

• To synthesize novel heterometallic chromium-lanthanide complexes using a dianionic 2,2′-biimidazolate bridging unit.
• To investigate the influence of different chelating ligands (N^N and N^N^N^N) on the structural and photophysical properties.
• To explore the potential of these complexes for light conversion applications, including downshifting and upconversion.

Main Methods:

• Synthesis of pseudo-octahedral [CrN6]+ chromophores by connecting 2,2′-biimidazolate to cis-[Cr(N^N)2]3+ or cis-[Cr(N^N^N^N)]3+ building blocks.
• Complexation of trivalent lanthanides (Ln3+) to form d-f adducts with varying stoichiometries.
• Characterization of photophysical properties, focusing on luminescence behavior with Eu(III) for downshifting and Er(III) for upconversion.

Main Results:

• Successfully synthesized heteroleptic pseudo-octahedral [CrN6]+ chromophores.
• Formed d-f {[(N^N)2Cr(biim)]nLn} (3+n)+, {[(N^N)2Cr(biim)]Ln(Tp)2}2+, and {[(N^N^N^N)Cr(biim)]Ln(Tp)2}2+ adducts.
• Demonstrated tunable light conversion properties by varying chelating ligands, achieving efficient Eu(III) downshifting and Er(III) upconversion.

Conclusions:

• The modular design of chromium-lanthanide complexes allows for control over their photophysical properties.
• The choice of chelating ligands significantly impacts the luminescence efficiency and type of light conversion.
• These heterometallic complexes show promise for applications in luminescent materials and photonics.