Ligand design and its influence on the photophysical and structural properties of dinuclear and tetranuclear copper and silver complexes

Abstract

Fluorescent molecules are used in a vast range of applications such as in organic light-emitting diodes (OLEDs) and thermally activated delayed fluorescence (TADF) emitters; however, many promising candidates lack the ability to fluoresce in the solid state which is needed in the manufacturing of these materials. Herein, the synthesis of a novel bidentate ligand, 2-methyl-N¬-((5-(2-(thiophen-2-yl)propan-2-yl)-1H-pyrrol-2-yl)methyl)propan-2-amine or SNNHtBu, and the corresponding dinuclear copper (I) and silver (I) complexes are reported with metal-metal bond interactions of 2.686 Å for [CuSNNHtBu]2 and 2.88 Å for [AgSNNHtBu]2. OLEDs and thermally activated delayed fluorescent (TADF) emitters are becoming a more common feature used in display technologies. A desire to move away from heavy and rare earth metals has made Copper (I) or CuI a desirable alternative. However, fine tuning of the excitation and emission properties of these complexes is of high importance. As such, we report the structural modification of a previously reported thiophene containing SNN dincuclear CuI complex. The synthesis, characterization, and fluorescent properties of two new ligands are investigated. Coordination of these two new ligands along with NNHtBu to CuI are conducted. These three new dinuclear CuI complexes are synthesized, characterized and their fluorescent and structural properties are compared and contrasted against themselves and the parent compound of [CuSNNHtBu]2. Copper assemblies play a vital role in biologal and synthetic processes alike. A recent advancement in extended metal chain assemblies has received significant attention due to their application in small molecule activation, in multielectron processes, and fluorescence. Schiff-base calix[2]pyrrole complexes for nickel (II) and palladium (II) have been previously reported for their use in hydrogen evolution. Herein, the utilization of symmetrical and unsymmetrical Schiff-base calix[2]pyrroles for coordination of Cu (I) to synthesize tetranuclear complexes is explored. By varying the substituents at the quaternary carbon, it was found that two different assemblies, either a distorted square-planar or a bent tetranuclear linear chain assembly were formed. Investigations also include looking into the effects of the imine on the system.