Detailed Molecular and Structural Analysis of Dual Emitter IrQ(ppy)2 Complex.

Iulia Corina Ciobotaru,Daniel Nicolae Crisan,Constantin Claudiu Ciobotaru,Silviu Polosan,Primoz Šket

doi:10.3390/ma13071617

Abstract

The molecular structure of the 8-hydroxyquinoline–bis (2-phenylpyridyl) iridium (IrQ(ppy)2) dual emitter organometallic compound is determined based on detailed 1D and 2D nuclear magnetic resonance (NMR), to identify metal-ligands coordination, isomerization and chemical yield of the desired compound. Meanwhile, the extended X-ray absorption fine structure (EXAFS) was used to determine the interatomic distances around the iridium ion. From the NMR results, this compound IrQ(ppy)2 exhibits a trans isomerization with a distribution of coordinated N-atoms in a similar way to facial Ir(ppy)3. The EXAFS measurements confirm the structural model of the IrQ(ppy)2 compound where the oxygen atoms from the quinoline ligands induce the splitting of the next-nearest neighboring C in the second shell of the Ir3+ ions. The high-performance liquid chromatography (HPLC), as a part of the detailed molecular analysis, confirms the purity of the desired IrQ(ppy)2 organometallic compound as being more than 95%, together with the progress of the chemical reactions towards the final compound. The theoretical model of the IrQ(ppy)2, concerning the expected bond lengths, is compared with the structural model from the EXAFS and XRD measurements.

Highlights

This paper proposes a complete investigation by High-performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR), extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD) techniques, to identify the chemical structure of IrQ(ppy)2 organometallic compound
Ir(III) complex 8-hydroxyquinoline–bis (2-phenylpyridyl) iridium (IrQ(ppy)2 ) organometallic compound was chemically synthesized with two types of ligand: 2-phenylpyridine and quinoline, in a standard two-step reaction procedure, described previously [7]
The earlier papers containing the X-ray crystal structures of the similar organometallic compounds reported a significant trans-effect of the Ir-C, which induces the formation of the Ir-Cl bridge bonds trans to the Ir-C bonds

Summary

Introduction

Starting with classical monoligand compounds containing quinoline (q) and phenylpyridine (ppy) derivatives, such as Alq and Ir(ppy) , which give single color electroluminescence [1,19], the architecture of these organometallics evolves towards more complex structures. These structures enable multicolor electroluminescence such as in the case of 8-hydroxyquinoline–bis (2-phenylpyridyl) iridium, known as IrQ(ppy) , with a general formula C31 H22 IrN3 O, or better external quantum efficiency in the OLED structures. The resulting compounds could form different molecular configurations close or far from the targeted structure

Objectives

Methods

Results