Fluorescent OLED Host-Guest Energy Transfer via Steric Protection

Solution Overview

Problem

In fluorescent light-emitting devices, the conversion of triplet excitation energy to singlet excitation energy is inefficient due to competing deactivation pathways, leading to reduced emission efficiency and reliability, particularly when using thermally activated delayed fluorescent materials as host materials with fluorescent materials as guest materials.

Innovation Solution

Incorporating a light-emitting layer with a host material and a guest material where the energy donor has a bulky structure and protecting groups to inhibit Dexter mechanism energy transfer, ensuring the triplet excitation energy is efficiently converted into singlet excitation energy, using materials with a five-membered ring skeleton and fluorescent acceptors with condensed aromatic rings and multiple protecting groups to maintain distance and prevent energy deactivation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If a fluorescent material is used as guest material in a light-emitting layer with a host material, then light emission is achieved, but triplet excitation energy of the host material is transferred to the T1 level of the guest material through Dexter mechanism, causing energy deactivation and reduced emission efficiency

Engineering Contradiction:

Improvetriplet excitation energy conversion efficiencyVSAvoidemission efficiency

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent applies local quality by introducing protecting groups specifically on the guest material molecules to create steric hindrance in localized regions. These protecting groups (such as alkyl groups, cycloalkyl groups, or aryl groups) are attached to specific positions on the guest material's molecular structure to prevent close approach between host and guest materials, thereby inhibiting the Dexter mechanism energy transfer pathway while maintaining overall system functionality.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent uses protecting groups as intermediary elements that mediate the interaction between host and guest materials. These protecting groups act as physical barriers that prevent direct contact between the host material's triplet excited state and the guest material's T1 level, thereby blocking the harmful energy transfer pathway without interfering with the desired light emission process.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Loss of energy

If the concentration of guest material is reduced to prevent energy transfer to T1 level, then emission efficiency improves, but luminance decreases due to quenching by degraded material and impurity

Engineering Contradiction:

Improvetriplet excitation energy conversion efficiencyVSAvoidluminance

Core Design Contradiction:

Loss of energyVSIllumination intensity

Solution Approach 1:

The patent applies local quality by introducing protecting groups specifically on the guest material molecules to create steric hindrance in localized regions. These protecting groups (such as alkyl groups, cycloalkyl groups, or aryl groups) are attached to specific positions on the guest material's molecular structure to prevent close approach between host and guest materials, thereby inhibiting the Dexter mechanism energy transfer pathway while maintaining overall system functionality.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent uses protecting groups as intermediary elements that mediate the interaction between host and guest materials. These protecting groups act as physical barriers that prevent direct contact between the host material's triplet excited state and the guest material's T1 level, thereby blocking the harmful energy transfer pathway without interfering with the desired light emission process.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Stability of the object's composition

If fluorescent material is used instead of phosphorescent material, then stability improves, but emission efficiency is reduced due to inefficient triplet excitation energy conversion

Engineering Contradiction:

Improvematerial stabilityVSAvoidtriplet excitation energy conversion efficiency

Core Design Contradiction:

Stability of the object's compositionVSLoss of energy

Solution Approach 1:

The patent uses protecting groups as intermediary elements that mediate the interaction between host and guest materials. These protecting groups act as physical barriers that prevent direct contact between the host material's triplet excited state and the guest material's T1 level, thereby blocking the harmful energy transfer pathway without interfering with the desired light emission process.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent applies parameter changes by modifying the molecular structure of the guest material through the introduction of protecting groups. This structural modification changes the energy levels and interaction parameters between host and guest materials, enabling efficient energy transfer from the host's triplet excited state to the guest's singlet excited state while preventing transfer to the guest's triplet state, thus improving overall emission efficiency while maintaining stability.

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

This approach enhances the emission efficiency and reliability of fluorescent light-emitting devices by preventing energy deactivation pathways, allowing for higher luminance and extended device lifespan while maintaining high power efficiency.

Implementation Method 1

In a thermally activated delayed fluorescent material, a singlet excited state is generated from a triplet excited state by reverse intersystem crossing

Methodology Applied

Scientific EffectReverse intersystem crossing:

Implementation Method 2

light emission from the singlet excited state is referred to as fluorescence

Methodology Applied

Scientific EffectFluorescence: Fluorescence

Implementation Method 3

energy transfer by the Dexter mechanism of energy transfer between a host material (energy donor) and a guest material (energy acceptor)

Methodology Applied

Scientific EffectDexter mechanism:

Data Source

PatentUS20250098526A1Light-emitting device, light-emitting apparatus, display device, electronic appliance, and lighting device

Publication Date: 2025.03.20 SEMICON ENERGY LAB CO LTD

AI summary

A light-emitting device with high emission efficiency and high reliability is provided. The light-emitting device includes a host material and a guest material in a light-emitting layer. The host material has a function of converting triplet excitation energy into light emission and the guest material emits fluorescence. The guest material has a molecular structure including a luminophore and protecting groups, and five or more protecting groups are included in one molecule of the guest materials. When the protecting groups are introduced into the molecule, triplet excitation energy transfer from the host material to the guest material by the Dexter mechanism is inhibited. As the protecting group, an alkyl group or a branched-chain alkyl group is used. A light-emitting device with improved emission efficiency can be obtained with the use of a material having a five-membered ring skeleton in the host material.