Cyclometallated Ir Complexes for OLED Emission Control

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Solution Overview

Problem

Current methods for preparing cyclometallated transition metal carbene complexes, particularly those with diaryl substituted carbene ligands, face challenges in controlling the cyclometallation isomer formation, leading to low yields and inefficiencies due to the predominance of either mer or fac isomers, which affects the performance of organic light-emitting diodes (OLEDs) in terms of color purity, efficiency, and operational lifetime.

Innovation Solution

A process is developed to prepare cyclometallated Ir complexes with diaryl substituted carbene ligands, where a substituent at the 2 position of the aryl residue bound to the carbene nitrogen atom is used to selectively form mainly the mer isomer, avoiding or reducing cyclometallation of the aryl residue with Ir, thereby achieving a predominantly single cyclometallation isomer and enhancing emission properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If conventional methods are used to prepare cyclometallated Ir complexes with diaryl substituted carbene ligands, then both mer and fac isomers are formed, but this leads to low yields and material loss due to the need for isomer separation

Engineering Contradiction:

Improveyield of cyclometallated Ir complexVSAvoidmaterial loss during isomer separation

Core Design Contradiction:

ProductivityVSLoss of substance

Solution Approach 1:

The patent introduces a substituent at the 2-position of the aryl residue bound to the carbene nitrogen atom. This structural parameter change in the carbene ligand selectively stabilizes the mer isomer through steric and electronic effects, causing the reaction to predominantly form the mer isomer (≥80% selectivity) without requiring subsequent separation processes, thereby improving yield and reducing material loss

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If multiple cyclometallation isomers are formed, then isomer separation is required, but this increases process complexity and reduces manufacturing efficiency

Engineering Contradiction:

Improvesimplicity of isomer separation processVSAvoidcomplexity of isomer separation

Core Design Contradiction:

Ease of manufactureVSDevice complexity

Solution Approach 1:

By modifying the carbene ligand structure with a substituent at the 2-position of the aryl residue, the patent changes the steric and electronic parameters of the ligand system. This parameter change creates a preferential pathway for mer isomer formation, eliminating the need for complex isomer separation processes and simplifying the manufacturing procedure

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If fac isomer predominates in the product mixture, then color purity and emission properties are compromised, but changing conditions to favor mer isomer without substitution increases process complexity

Engineering Contradiction:

Improvecolor purity of emissionVSAvoidprocess complexity to control isomer ratio

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent employs a specific structural parameter change - introducing a substituent at the 2-position of the aryl residue bound to the carbene nitrogen atom. This substitution creates steric hindrance and electronic effects that selectively stabilize the mer isomer configuration, ensuring high color purity and optimal emission properties while maintaining straightforward reaction conditions without additional process complexity

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The process allows for the isolation of mer isomers with short emission decay times, improving radiative processes and making these complexes suitable for OLEDs with high efficiency, long operational lifetime, and reduced material loss during isomer separation.

Implementation Method 1

The phosphorescent emitters are typically organometallic complexes which exhibit triplet emission in contrast to the fluorescent emitters which exhibit singlet emission

Methodology Applied

Scientific EffectPhosphorescence: Phosphorescence

Implementation Method 2

a substituent at the 2 position of the aryl residue bound to the carbene nitrogen atom is used to selectively form mainly the mer isomer, avoiding or reducing cyclometallation of the aryl residue with Ir

Methodology Applied

Scientific EffectSteric effect:

Implementation Method 3

Methodology Applied

Scientific EffectElectronic effect:

Implementation Method 4

Methodology Applied

Scientific EffectRadiative decay:

Data Source

PatentEP3126371B1Metal complexes, comprising carbene ligands having an o-substituted non-cyclometalated aryl group and their use in organic light emitting diodes

Publication Date: 2021.11.10 UDC IRELAND

AI summary

Cyclometallated Ir complex comprising three N,N diaryl substituted carbene ligands, bearing substituents in the 2 position of the non-cyclometallated aryl ring;an organic electronic device, preferably an organic light-emitting diode (OLED), comprising at least one cyclometallated Ir complexas described above, a light-emitting layer comprising said cyclometallated Ir complex preferably as emitter material, preferably in combination with at least one host material, use of said cyclometallated Ir complex in an OLED and an apparatus selected from the group consisting of stationary visual display units, mobile visualdisplay units, illumination units, units in items of clothing, units in handbags, units in accessoires, units in furniture and units in wallpaper comprising said organic electronic device, preferably said OLED, or said light-emitting layer. The present invention further relates to a process for the preparation of said cyclometallated Ir complex.