Introducing sterically demanding substituents and π-π-interactions into [Cu(P^P)(N^N)]⁺ complexes

Area of Science:

• Coordination Chemistry
• Materials Science
• Photophysics

Background:

• 2,2'-bipyridine (bpy) ligands are crucial in coordination chemistry for metal binding.
• Tuning steric and electronic properties of bpy ligands influences complex photophysical behavior.
• Copper complexes with bisphosphane ligands (P^P) are explored for luminescence applications.

Purpose of the Study:

• Synthesize and characterize novel N^N chelating ligands based on 2,2'-bipyridine.
• Incorporate these ligands into heteroleptic copper(I) complexes of the type [Cu(P^P)(N^N)][PF6].
• Investigate the impact of ligand substituents on the photophysical properties, particularly photoluminescence quantum yields (PLQYs).

Main Methods:

• Synthesis and characterization of ten N^N chelating ligands with sterically hindering substituents.
• Formation of 15 heteroleptic copper(I) complexes using wide bite-angle bisphosphane ligands (POP or xantphos).
• Photophysical studies including solid-state emission maxima and PLQY measurements.
• Single crystal X-ray diffraction for structural analysis of 12 complexes.

Main Results:

• Ten new N^N chelating ligands and 15 copper(I) complexes were synthesized and characterized.
• Solid-state emission maxima for the complexes ranged from 518 to 567 nm.
• The highest PLQYs were observed for complexes with 6,6'-disubstituted bpy ligands featuring phenyl moieties connected via ethylene or propylene spacers.
• [Cu(POP)((2-PhEt)2bpy)][PF6] achieved a PLQY of 67%, and [Cu(POP)((3-PhPr)2bpy)][PF6] reached 72%.

Conclusions:

• Steric hindrance and tethered phenyl groups in bpy ligands significantly influence the photophysical properties of copper(I) complexes.
• The developed copper complexes exhibit high PLQYs, among the best reported for this class of compounds.
• These findings offer a pathway for designing highly efficient luminescent copper complexes for potential applications.