Luminescent copper(i) complexes with bisphosphane and halogen-substituted 2,2'-bipyridine ligands

Area of Science:

• Coordination Chemistry
• Materials Science
• Photophysics

Background:

• Heteroleptic copper(I) complexes are investigated for their luminescent properties.
• Tuning ligand steric and electronic properties influences complex geometry and emission characteristics.
• Halo-substituted 2,2'-bipyridine ligands are explored to stabilize tetrahedral copper(I) complexes.

Purpose of the Study:

• Synthesize and characterize novel heteroleptic copper(I) complexes with varying halo-substituted bipyridine ligands.
• Investigate the structural, electrochemical, and photophysical properties of these complexes.
• Evaluate the performance of selected complexes as luminophores in light-emitting electrochemical cells (LECs).

Main Methods:

• Synthesis of heteroleptic [Cu(P^P)(N^N)][PF6] complexes using POP or xantphos and halo-substituted bpy ligands.
• Single crystal X-ray diffraction for structural determination, including pressure dependence studies.
• Electrochemical and photophysical measurements, supported by Density Functional Theory (DFT) calculations.

Main Results:

• Novel copper(I) complexes with halo-substituted bipyridines (6,6'-Cl2bpy, 6-Brbpy, 6,6'-Br2bpy) were successfully synthesized.
• Structural analysis confirmed tetrahedral geometry, influenced by ligand substitution.
• Complexes displayed orange-to-red emission in solution and yellow-to-orange in solid state, with DFT correlating emission to triplet state geometry.
• [Cu(POP)(6,6'-Cl2bpy)][PF6] and [Cu(xantphos)(6,6'-Cl2bpy)][PF6] achieved solid-state photoluminescence quantum yields of 15% and 17%, respectively.
• These complexes functioned as efficient luminophores in LECs, exhibiting orange electroluminescence with rapid turn-on times (<5–12 s).
• Maximum luminance values of 121 and 259 cd m-2 were recorded, with external quantum efficiencies of 1.2%.

Conclusions:

• The steric bulk of halo-substituted bipyridine ligands effectively stabilizes tetrahedral copper(I) complexes.
• Ligand substitution patterns significantly impact the emission properties and triplet state geometry.
• [Cu(POP)(6,6'-Cl2bpy)][PF6] and [Cu(xantphos)(6,6'-Cl2bpy)][PF6] demonstrate potential for applications in LECs due to their efficient electroluminescence and fast response times.