Cu@Core in the Cu₃C₃ Ring with 2-bdppmapy: A High-Quantum-Yield Planar Hexagonal Cu(I) Metallacycle

Area of Science:

• Coordination Chemistry
• Materials Science
• Optoelectronics

Background:

• Copper(I) complexes show promise for optoelectronics but suffer from oxidation sensitivity and low photoluminescence quantum yields (PLQYs).
• Existing phosphine-alkynyl strategies improve stability but structural distortions in Cu4 clusters limit PLQYs.
• Conventional open-cube Cu4 clusters exhibit structural limitations hindering high PLQY.

Purpose of the Study:

• To engineer novel copper(I) complexes with enhanced photophysical properties for optoelectronic applications.
• To overcome the limitations of structural distortions and low PLQYs in tetranuclear copper clusters.
• To investigate the structure-property relationships in planar copper clusters for improved luminescence.

Main Methods:

• Ligand engineering using a bidentate diphosphine (N,N-bis((diphenylphosphino)methyl)-2-pyridinamine) to synthesize planar tetranuclear copper clusters.
• Single-crystal X-ray diffraction to determine the precise molecular structure and planarity.
• Photoluminescence spectroscopy and lifetime measurements to characterize emission properties and excited states.
• Theoretical calculations to elucidate the origin of vibronically structured emission.

Main Results:

• Synthesis of planar tetranuclear copper clusters [(2-bdppmapy)3Cu4(μ3-PhC≡C)3]X with a near-perfect coplanar Cu3C3@Cu hexagonal ring.
• Exceptional planarity (mean deviation: 0.025 Å) and strong cuprophilic interactions (Cu···Cu: 2.387-2.441 Å) were observed.
• Achieved unprecedented solid-state PLQY up to 93% with turquoise emission (λmax = 483 nm) and microsecond-scale lifetimes (τ ≈ 22 μs).
• Structured emission attributed to ν(C═C) and ν(C≡C) vibrations from phenylacetylene ligands, originating from T1 triplet excited states.

Conclusions:

• The rigid, planar architecture of the novel copper clusters maximizes electronic delocalization, leading to high PLQYs.
• The developed ligand strategy successfully addresses structural distortions, enabling efficient luminescence in copper(I) complexes.
• These findings pave the way for advanced optoelectronic materials based on highly emissive and stable copper clusters.