Substituted Indenofluorene Polymers for OLED Host Materials
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Solution Overview
Problem
Conjugated polymers are unsuitable as host materials for blue and green triplet emitters in organic electroluminescent devices due to quenching issues, leading to short lifetimes and low emission efficiency, while non-conjugated polymers have inadequate solubility, making inexpensive production processes like rotation coating or print coating impractical.
Innovation Solution
A polymer with a structural unit that allows for high emission efficiency of blue, green, and red triplet emitters without quenching, featuring a specific chemical structure that adjusts solubility for simple and inexpensive production processes, enabling the use of these polymers as host materials in organic electroluminescent devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conjugated polymers are used as host materials, then solubility and ease of production are improved, but emission efficiency and lifetime are worsened due to quenching of triplet emitters
Solution Approach 1:
The patent modifies the chemical structure of fluorene units by introducing specific substituents (such as dibenzofuran, dibenzothiophene, carbazole groups) to change the electronic and steric parameters of the polymer. This structural modification achieves optimal balance between solubility (for easy production) and triplet energy level (to prevent quenching), thereby resolving the contradiction between ease of manufacture and emission efficiency.
Solution Approach 2:
The patent creates composite polymer structures by combining fluorene backbone units with various functional substituents (electron-donating, electron-withdrawing, bulky groups). These composite structures integrate multiple functions: maintaining conjugation for solubility while incorporating high-energy units to prevent triplet quenching, thus achieving both ease of manufacture and high emission efficiency.
2Reliability
If non-conjugated polymers are used to avoid quenching, then emission efficiency is improved, but solubility and lifetime are worsened
Solution Approach 1:
The patent introduces bulky substituents (such as tert-butyl groups, long alkyl chains) and heteroatomic groups (O, S, Si) to change the steric and electronic parameters of the polymer chain. These modifications increase intermolecular spacing and reduce aggregation, thereby improving solubility while maintaining the non-conjugated structure that prevents triplet quenching and ensures high emission efficiency.
3Reliability
If small molecules are used in OLEDs, then emission efficiency and lifetime are improved, but device complexity and production cost are worsened
Solution Approach 1:
The patent designs polymers that can serve multiple functions: they act as both the host material and the structural matrix for OLED devices. The polymer backbone provides mechanical stability, the substituents tune the energy levels for efficient triplet emission, and the overall structure enables solution processing. This multi-functionality eliminates the need for separate host and emitter layers, simplifying device fabrication while maintaining high emission efficiency and lifetime.
Data Source
AI summary
The present invention relates to polymers which contain substituted indenofluorene derivatives as structural unit, to substituted indenofluorene derivatives, to a process for the preparation of the polymers according to the invention, to mixtures and solutions which comprise the polymers according to the invention, and to the use of the polymers according to the invention in electronic devices, in particular in organic electroluminescent devices, so-called OLEDs (OLED=organic light emitting diode).