Diamine ligands with multiple coplanar conjugation rings and their phosphorescent copper complexes: Synthesis, characterization, crystal structures, and photophysical property

In this paper, we report a series of diamine ligands with multiple coplanar conjugation rings and their corresponding phosphorescent Cu(I) complexes, including their synthesis, crystal structures, photophysical properties, and electronic nature. Geometric parameters suggest that the Cu(I) center localizes at a distorted tetrahedral geometry within the Cu(I) complexes. Theoretical calculation reveals that all emissions originate from triplet metal-to-ligand-charge-transfer excited state. It is found that the free rotation of conjugation rings may compromise the coplanar plane and thus has little effect on the photophysical property of their corresponding Cu(I) complexes. But excess coplanar conjugation moiety is harmful for emissive state. The detailed quenching mechanism is investigated.