Divalent Lanthanide Coordination Compounds for Stable Blue OLED Emitters
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current electroluminescent devices using organic light emitting diodes (OLEDs) face inefficiencies due to the lack of stable blue emitters, particularly thermally activated delayed fluorescence (TADF) and phosphorescence (Ph) emitters, which suffer from chemical instability and broad emission spectra, incompatible with fast display refresh rates and color purity requirements.
Innovation Solution
Development of electroluminescent coordination compounds featuring divalent lanthanides like Europium (Eu2+) and Ytterbium (Yb2+) stabilized by macrocyclic organic ligands, preventing oxidation and maintaining deep blue, narrow emission spectra, thus overcoming chemical instability and spectral broadness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If TADF or Ph blue emitters are used, then light emission efficiency is improved, but chemical stability deteriorates due to charge-separated states weakening chemical bonds
Solution Approach 1:
The patent introduces a heavy metal center (Iridium, Osmium, Gold, or Platinum) as an intermediary that mediates the excitation energy. The exciton resides on the heavy metal cation rather than on organic bonds, allowing efficient light emission while avoiding chemical bond weakening. The heavy metal acts as a stable platform that can accommodate charge-separated states without compromising molecular integrity.
Solution Approach 2:
The patent changes the fundamental parameter of where the exciton is localized - from organic ligand to heavy metal center. This parameter change transforms the emission mechanism while improving stability. The heavy metal's f-orbitals provide the necessary electronic structure for efficient emission without the chemical bond weakness inherent in organic-based TADF and Ph emitters.
2Use of energy by moving object
If TADF or Ph emitters are used, then light emission is achieved, but emission spectra become broad reducing color purity
Solution Approach 1:
The patent applies local quality by concentrating the emission origin at a specific local position - the heavy metal center - rather than distributing it across flexible organic bonds. This localization restricts the range of energetic states and produces narrow emission spectra with high color purity, while the heavy metal's electronic structure maintains efficient light emission.
3Reliability
If three-valent lanthanides are used, then chemical stability is improved, but excited state lifetime becomes too long for display applications
Solution Approach 1:
The patent changes the oxidation state parameter from +3 to +2 for the lanthanide center. This parameter change simultaneously achieves short excited state lifetime (microsecond range suitable for displays) while maintaining chemical stability through the divalent oxidation state, resolving the contradiction between stability and lifetime.
4Duration of action of moving object
If divalent lanthanides are used, then excited state lifetime is shortened, but chemical stability deteriorates due to oxidation tendency
Solution Approach 1:
The patent uses macrocyclic organic ligands as intermediaries that stabilize the divalent lanthanide center. These ligands act as protective intermediaries that prevent oxidation of the divalent lanthanide while allowing it to maintain its short excited state lifetime. The ligand field provides the necessary stabilization without compromising the electronic properties needed for efficient emission.
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 coordination compounds provide stable, efficient deep blue emission with short excited state lifetimes, suitable for OLEDs and other opto-electronic devices, enhancing color purity and operational stability.
Implementation Method 1
divalent lanthanide coordinated by a cyclic organic ligand
Implementation Method 2
electroluminescent coordination compound
Implementation Method 3
intra-atomic transitions in the blue, green, and red spectral region based on Thulium (Tm3+), Terbium (Ter3+) and Europium (Eu3+) respectively have been demonstrated
Implementation Method 4
The presence of heavy metal elements softens the selection rules for the excited states and allows triplet excitons to emit light too; known as phosphorescence (Ph)
Implementation Method 5
thermally activated delayed fluorescence (TADF) has been used wherein by thoughtful design of the organic emitter molecule, the energy difference between the non-emissive triplet and the emissive singlet exciton is engineered to be very small. This allows triplets to thermally convert into singlet excitons and thereby contribute to light emission
Data Source
AI summary
A metal-organic coordination compound, wherein the coordination compound comprises at least one divalent lanthanide coordinated by a cyclic organic ligand according to formula 1:whereini is larger than 3; andn is equal to 1, 2, or 3; andL for each occurrence is independently selected fromdivalent cyclic organic groups that can be substituted and that are formed by removing two hydrogen atoms from an organic cyclic molecule that can be substituted,arylenes, preferably 5- or 6-membered ring aromatic or heteroaromatic group, orbiradical fragments ofandX is independently selected for each occurrence from the group of:wherein R1 and R2 are hydrogen or any covalently bound substituents being identical or different in each occurrence; andwherein R1 and/or R2 are at least in 3 occurrences not hydrogen, andwherein two groups R2 can be covalently linked with each other, thereby forming a further cyclic element,it also being possible that two cyclic organic ligands of formula 1 are covalently linked with each other by one or two divalent linking groups which divalent linking groups are formed of one R1 of each of the two cyclic organic ligands of formula 1 that are covalently linked with each other.