Tethered NBN OLED Emitters for Higher PLQY and Stability
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Solution Overview
Problem
Existing organic light-emitting diodes (OLEDs) face challenges with low photoluminescence quantum yield (PLQY) due to non-radiative decay pathways and instability of imidazole C—N bonds, which affect device lifetime.
Innovation Solution
Tethering B-aryl and neighboring imidazole rings in NBN ligands to decrease molecular vibrations and enhance kinetic stability by introducing a substituent for out-of-plane orientation, improving the hydrolytic stability of the NBN ligand class.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional NBN ligands are used in Ir(NBN)3 complexes, then the device can be fabricated with standard materials, but the photoluminescence quantum yield is low due to non-radiative decay pathways
Solution Approach 1:
The patent modifies the molecular structure of NBN ligands by changing geometric parameters - specifically tethering the B-aryl group to the imidazole ring at specific positions (2,7 or 3,6) with controlled bond lengths and angles. This structural parameter change restricts molecular vibrations and reduces non-radiative decay pathways, thereby improving photoluminescence quantum yield from conventional values to above 25%.
Solution Approach 2:
The patent creates a composite ligand structure combining the B-aryl group, imidazole ring, and tethering linkage into a unified NBN ligand system. This composite structure works synergistically to both stabilize the complex and enhance photoluminescence properties, achieving both structural stability and high quantum yield simultaneously.
2Ease of manufacture
If the imidazole C—N bond is used in the ligand structure, then the ligand can be synthesized, but the bond lacks kinetic stability which affects device lifetime
Solution Approach 1:
The patent changes the chemical parameters of the imidazole C—N bond by introducing electron-withdrawing or electron-donating substituents at specific positions on the imidazole ring. This modifies the bond dissociation energy and kinetic stability, making the C—N bond more resistant to hydrolysis and degradation, thereby extending device lifetime while maintaining synthesizability.
Solution Approach 2:
The tethering linkage acts as an intermediary between the B-aryl group and the imidazole ring, providing both structural connection and electronic modulation. This intermediary structure protects the imidazole C—N bond from direct attack while maintaining the overall ligand functionality, thus enhancing stability without compromising synthesis.
3Device complexity
If the B-aryl group is oriented in-plane with the imidazole ring, then the ligand structure is simple, but the hydrolytic stability is insufficient
Solution Approach 1:
The patent introduces asymmetric tethering where the B-aryl group is connected to the imidazole ring at non-equivalent positions (2,7 or 3,6) with controlled stereochemistry. This asymmetric arrangement creates a rigid, three-dimensional configuration that enhances hydrolytic stability by preventing planar conformation, while the complexity increase is localized and manageable.
Solution Approach 2:
The patent transitions the B-aryl group from a two-dimensional in-plane orientation to a three-dimensional out-of-plane orientation through the tethering linkage. This dimensional change creates steric protection and enhances hydrolytic stability by preventing approach of nucleophiles to the C—N bond, while the added structural complexity is confined to the tethering region only.
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 proposed method increases the photoluminescence quantum yield and enhances the stability of the Ir(NBN)3 family, leading to improved device performance and longevity.
Implementation Method 1
decrease molecular vibrations responsible for non-radiative decay pathways responsible for the low PLQY of the Ir(NBN)3 family
Implementation Method 2
impart hydrolytic stability to the NBN ligand class
Data Source
AI summary
The present disclosure provides a compound including a first ligand LA of Formula I,In Formula I, ring A is a 7 to 12-membered heterocyclic ring that is fused to ring B, which is a 5-membered or 6-membered heterocyclic ring; ring C is a 5- or 6-membered ring; n is 1 or 2; X is selected from B, N, Al, In, and Ga; each W is selected from NR, O, S, Se, SO, SO2, BR, CRR′, C═CRR′, SiRR′, PRR′, and GeRR′; each of Z1, Z2, and Z3 is independently C or N; at least one of Z1, Z2, and Z3 is N; each R, R′, RA, RB, and RC is hydrogen or general substituent; each of K1 and K2 is a direct bond, O, or S; LA is coordinated to a metal M. Formulations, OLEDs, and consumer products containing the compound are also disclosed.