Heteroleptic light-emitting copper(I) complexes with possible applications in light-emitting electrochemical cells

Abstract

The overall aim of this project was the design, synthesis and characterization of copper(I) complexes that, upon excitation, emit light in the region of the electromagnetic spectrum that is visible to the human eye. The complexes are incorporated into light-emitting devices and their electroluminescent behaviour was studied and the results used to further optimize the compounds in an iterative manner. The main focus was on complexes of the general formula [Cu(P^P)(N^N)][PF6], where P^P is a chelating bisphosphane and N^N is a 2,2'-bipyridine (bpy), phenanthroline or moiety of similar structure. The commercially available bisphosphanes, bis(2-(diphenylphosphino)phenyl)ether (POP) and 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos) were chosen as our standard P^P chelating ligands in order to investigate the role of the N^N chelating ligand and study the effects of modifications on the bpy or its derivatives on the copper complexes. Detailed structural, photophysical and electrochemical characterizations, as well as quantum chemical calculations of the synthesized complexes were carried out and the most promising compounds were evaluated in light-emitting electrochemical cells (LECs). In order to make the reader familiar with the topic, we start with the motivation for this project and continue with an introduction about general properties of copper and its emissive complexes. The principle of thermally activated delayed fluorescence (TADF) is explained and the characteristics of LECs are described. In Chapter I, a series of complexes with alkyl substituents in different positions in the bpy and phen ligands are compared. In Chapter II, the results of the investigation of complexes with chloro-and bromo-substituted bpy ligands are shown. The effect of CF3 substitution in the bpy on complex and device properties is exposed in Chapter III. The subject of Chapter IV is the fortuitous formation of an inorganic coordination polymer. The potential of an alkyl phosphane as a ligand for emissive copper(I) complexes was evaluated and the resulting complexes are shown in Chapter V. A side project with dimeric silver(I) complexes and their self-assembling properties is presented in Chapter VI. The thesis is concluded with an outlook about projects for the near future and the potential of copper(I) based light-emitting electrochemical cells as an illumination technique is discussed.