2,5-linked polyfluorenes for OLED triplet energy
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Solution Overview
Problem
The low triplet energies of 2,7-linked polyfluorene materials limit the incorporation of transition metal complexes that can emit red or orange light, restricting the color range of phosphorescent emitters in OLED devices.
Innovation Solution
Development of 2,5-disubstituted fluorene monomers and polymers with higher triplet energies by introducing polymerizable substituents at the 2- and 5-positions, allowing for head-to-tail polymerization and incorporation of 2,5-fluorene units to create oligomers and polymers with increased singlet and triplet energies, enabling broader color emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If 2,7-linked polyfluorene materials are used in OLED devices, then good charge transport properties and excellent film forming properties are achieved, but the triplet energy is limited to low values that restrict the color range of phosphorescent emitters
Solution Approach 1:
The patent changes the chemical structure parameter of polyfluorene by switching from 2,7-linkage to 2,5-linkage of fluorene units. This structural parameter change directly increases the triplet energy from approximately 2.1 eV in 2,7-linked polymers to higher values in 2,5-linked polymers, thereby expanding the color range of compatible phosphorescent emitters while maintaining other desirable properties
Solution Approach 2:
The patent creates composite materials by incorporating transition metal complexes (phosphorescent emitters) into the 2,5-linked polyfluorene host matrix. The higher triplet energy of the host material enables compatibility with a broader range of phosphorescent emitters including those emitting red, orange, and green light, achieving synergistic enhancement of device performance and color range
2Use of energy by moving object
If transition metal complexes are incorporated into 2,7-linked polyfluorene OLED devices, then nearly 100% internal quantum efficiency can be achieved, but only red or orange light emission is possible due to low triplet energies
Solution Approach 1:
By changing the linkage pattern from 2,7 to 2,5, the patent modifies the triplet energy parameter of the host polymer to a higher value. This enables the system to maintain high internal quantum efficiency with transition metal complexes while simultaneously expanding the color range to include green, blue, and other wavelengths that were previously inaccessible with 2,7-linked polymers
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 resulting materials enhance the ability to incorporate transition metal complexes for efficient light emission from both singlet and triplet excitons, potentially achieving nearly 100% internal quantum efficiency and expanding the color range of OLED devices.
Implementation Method 1
introducing polymerizable substituents at the 2- and 5-positions, allowing for head-to-tail polymerization and incorporation of 2,5-fluorene units to create oligomers and polymers with increased singlet and triplet energies
Implementation Method 2
Transition metal complexes, by virtue of spin-orbit coupling, can radiatively decay with an efficiency that competes with non-radiative pathways
Implementation Method 3
When these complexes are incorporated into polymeric OLED devices it is possible to achieve nearly 100% internal quantum efficiency since both singlet and triplet excitons produced in the device can emit light
Implementation Method 4
In an OLED device, electrons and holes injected from the cathode and anode respectively combine in an emissive layer producing singlet and triplet excitons that can decay radiatively producing light
Data Source
AI summary
Polyfluorene polymers and copolymers having substantial amounts (10-100%) of fluorenes coupled at the 2 and 5 positions of fluorene are useful as active layers in OLED devices where triplet energies > 2.10 eV are required.