Diphosphane-Mediated Control of the Emissive Properties in [Cu(NHC)(P^P)]⁺ Complexes: TADF vs Phosphorescence

Area of Science:

• Materials Science
• Photophysics
• Coordination Chemistry

Background:

• Thermally Activated Delayed Fluorescence (TADF) emitters are crucial for efficient optoelectronics.
• Copper complexes with N-heterocyclic carbene (NHC) and diphosphane ligands offer tunable photophysical properties.
• Understanding ligand influence is vital for designing high-performance TADF materials.

Purpose of the Study:

• To investigate the impact of diphosphane skeleton and substituents on the photophysical properties of [Cu(NHC)(P^P)]PF6 TADF-phosphorescent emitters.
• To identify key structural factors governing quantum yield (Φ) and energy gaps.
• To explore ligand engineering strategies for optimizing TADF emitter performance.

Main Methods:

• Synthesis and characterization of [Cu(NHC)(P^P)]PF6 complexes with varying NHC (Bz-Im-2-XPy, X = H, Cl) and diphosphane ligands.
• Photophysical measurements including quantum yield determination.
• Analysis of structure-property relationships, considering energy gaps (ΔE(S1-T1)), steric factors, and T1 energies.

Main Results:

• Ligand engineering, particularly the diphosphane skeleton, significantly influences photophysical properties.
• Quantum yields up to 85% were achieved by optimizing diphosphane structure and using simple carbene frameworks.
• The diphosphane skeleton was identified as the most critical factor for controlling quantum yield, surpassing energy gaps or steric effects.

Conclusions:

• The diphosphane skeleton is the primary determinant of quantum yield in these copper-based TADF emitters.
• Simple structural modifications of ligands can lead to substantial improvements in emitter efficiency.
• This study provides new strategies for designing high-performance TADF emitters through rational ligand design.