Three-Coordinated Heteroleptic Cu(I) Complexes with Bulky Phosphine Ligands: Influence of Substituents on Photophysical Properties

The design and synthesis of cost-effective and environmentally friendly luminescent materials have great implications and challenges. In this study, bulky phosphine ligands (Sphos and Xphos) are utilized to synthesize a series of three-coordinated Cu(I) complexes with different N^N ligands derived from 1,10-phenanthroline. By employing rigid N^N donor ligands featuring different electron-donating or withdrawing substituents, the emission from 585 to 698 nm with a microseconds lifetime in the solid state can be systematically modulated. While complexes 1–3 with 1,10-phenanthroline and neocuproine exhibit emission around 590 nm, dicnq (featuring electron-withdrawing groups) coordinated complexes 4 and 5 exhibit significantly redshifted emissions to ≈700 nm. The experimental and theoretical studies suggest the occurrence of thermally activated delayed fluorescence with microseconds lifetime and a small ΔE_ST. This investigation highlights the pivotal role of ligand design in regulating the photophysical characteristics of Cu(I) complexes.