Two Luminescent Iridium Complexes with Phosphorous Ligands and Their Photophysical Comparison in Solution, Solid and Electrospun Fibers: Decreased Aggregation-Caused Emission Quenching by Steric Hindrance

Chaohui Huang,Bin Li

doi:10.3390/ma14185419

Abstract

In this paper, we prepared two phosphorescent Ir complexes with ligands of 2-phenyl pyridine (ppy), and two phosphorous ligands with large steric hindrance, hoping to allow enough time for the transformation of the highly phosphorescent 3MLLCT (metal-to-ligand-ligand-charge-transfer) excited state. Their large steric hindrance minimized the π-π interaction between complex molecules, so that the aggregation-induced phosphorescence emission (AIPE) influence could be minimized. Their single crystals indicated that they took a distorted octahedral coordination mode. Photophysical comparison between these Ir complexes in solution, in the solid state and in electrospun fibers was performed to confirm the realization of limited aggregation-caused quenching (ACQ). The potential surface crossing and energy transfer from 3MLBPECT/3MLBPELppyCT to 3MLppyCT in these Ir complexes were revealed by density functional theory calculation and temperature-dependent emission. It was confirmed that these two phosphorous ligands offered large steric hindrance, which decreased the ACQ effect, allowing the efficient emissive decay of the 3MLppyCT excited state. This is one of the several luminescent Ir complexes with a high emission yield (Φ = 0.27) and long emission lifetime (0.43 μs) in the solid state.

Highlights

The development of optoelectronic techniques has attracted research attention for luminescent materials with unique optoelectronic features [1]
As we mentioned a large stericmay hinimprove the emissive performance of in the solid state by drance may improve the emissive performance of Ir(ppy)2(BPE) and Ir(ppy)2(TPP) in the reducing the effect, which will be discussed below
The potential surface crossing and energy transfer from 3 MLBPE CT/3 MLBPE Lppy CT to 3 MLppy CT in these Ir complexes was revealed by density functional theory calculation and temperature-dependent emission

Summary

Introduction

The development of optoelectronic techniques has attracted research attention for luminescent materials with unique optoelectronic features [1]. A luminescent Ir complex is composed of a central Ir(III) ion and three bidentate chelating ligands, forming an octahedral coordination structure. These three bidentate chelating ligands may be homogeneous ones (three CN chelating ligands) or heterogeneous ones (two CN and one LX chelating ligands). The photophysical performance of resulting Ir(CN) and Ir(CN) (LX) complexes is usually dominated and affected by the major ligand, including its molecular structure and conjugation size, while the auxiliary ligand exerts its moderate effect on photophysical performance, so that some desired features can be modified or enhanced, with emission features well preserved [4,5]

Methods

Results

Conclusion