Liquid crystalline copper(i) complexes with bright room temperature phosphorescence

Abstract

Phosphorescence in the liquid crystal state with one of the highest quantum yield values, 42%, at room temperature is reported. This property is achieved with cyclic trinuclear copper(I) complexes prepared using 3,5-dimethyl-4-(trialkoxyphenyl)pyrazolate ligands. The compounds show well-organized hexagonal columnar mesophases that are stable at room temperature or near room temperature with intracolumnar order at distances of 3.6 Å, red emission and lifetimes consistent with the excimeric metal-centered phosphorescence typical of copper trinuclear pyrazolato complexes. A non-mesogenic analogue shows similar properties, and the single crystal structure is formed by stacked molecules forming a supramolecular extended structure with two different intermolecular Cu⋯Cu contacts, 3.368 Å and 3.666 Å, which are in the range of previously reported weak cuprophilic interactions. The results demonstrate that metallomesogens with efficient room temperature phosphorescence can be obtained with metal complexes other than the widely explored and precious metal-based iridium or platinum complexes.