Neutral Osmium II Complexes for Stable OLED Phosphorescence
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Solution Overview
Problem
Current organic light-emitting diodes (OLEDs) and polymer light-emitting diodes (PLEDs) face limitations in achieving high internal quantum efficiency due to the inefficient use of singlet and triplet excitons, with red and blue emitters being particularly challenging to develop, leading to instability and long response times.
Innovation Solution
Design and synthesis of new Os(II) emitting complexes with anionic chelating ligands such as 3-trifluoromethyl-5-(2-pyridyl)pyrazolate and donor ligands like carbonyl, pyridine, and phosphine to create neutral Os(II) complexes that balance charge and promote efficient intersystem crossing, enabling the use of both singlet and triplet excitons for enhanced emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional ionic Os(II) complexes are used as dopant emitters, then the device can be fabricated, but the device performance is inferior with instability and long response time due to ion drifting under high electric field
Solution Approach 1:
The patent changes the charge state parameter of the Os(II) complex from positive (ionic) to neutral by selecting ligands with appropriate donor/acceptor properties. This parameter change eliminates the drifting issue under high electric field, thereby improving device stability and reducing response time.
Solution Approach 2:
The patent creates composite ligand systems combining electron-donating ligands (such as carbonyl, phosphine, arsine) with electron-accepting ligands (such as pyridine, bipyridine, and anionic chelating ligands like fppz−, bptz−, pyN4−). This composite ligand structure balances the charge at the Os(II) center to achieve neutrality while maintaining stable coordination.
2Use of energy by moving object
If organic or polymer LEDs use fluorescence emission mechanism, then the device can operate, but the internal quantum efficiency is capped at 25% due to spin statistics
Solution Approach 1:
The patent replaces the fluorescence emission mechanism (spin-allowed singlet state decay) with phosphorescence emission mechanism (spin-forbidden triplet state decay enabled by heavy metal effect). This substitution allows utilization of both singlet and triplet excitons, breaking the 25% efficiency limit.
Solution Approach 2:
The patent changes the emission mechanism parameter from fluorescence to phosphorescence by introducing Os(II) complex with heavy metal effect. This parameter change enables efficient intersystem crossing from singlet to triplet state and facilitates triplet exciton radiative decay, achieving internal quantum efficiency exceeding 25%.
3Use of energy by moving object
If red emitting complexes are designed with traditional ionic Os(II) structures, then the complexes can be synthesized, but the luminescence quantum yield is low due to ionic nature and lack of strong covalent bonding
Solution Approach 1:
The patent changes the bonding character parameter from ionic to covalent by selecting ligands that form strong covalent bonds with the Os(II) center. The combination of anionic chelating ligands and neutral donor ligands creates strong covalent coordination, enhancing both stability and luminescence quantum yield.
Solution Approach 2:
The patent employs composite ligand structures combining chelating ligands (fppz−, bptz−, pyN4−) with donor ligands (carbonyl, phosphine, arsine, pyridine, bipyridine). This composite ligand system provides both strong covalent bonding for stability and appropriate electronic properties for high luminescence quantum yield.
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 Os(II) complexes achieve high internal quantum efficiencies and stability, allowing for the production of efficient red, green, and blue phosphorescent emissions, improving the performance of OLEDs and PLEDs by stabilizing the Os(II) center and enhancing energy transfer and carrier trapping.
Implementation Method 1
Phosphorescent Osmium (II) complexes and uses thereof
Implementation Method 2
The strong spin-orbit coupling induced by these heavy metal ions promotes an efficient intersystem crossing from the singlet to the triplet state
Implementation Method 3
The strong spin-orbit coupling induced by these heavy metal ions promotes an efficient intersystem crossing from the singlet to the triplet state
Implementation Method 4
enhancing energy transfer and carrier trapping
Data Source
AI summary
There is disclosed herein phosphorescent compounds, uses thereof, and devices including organic light emitting diode (OLEDs) including such compounds.Compounds of interest include:wherein A is Os or RuThe anionic chelating chromophores N^N, which are formed by connecting one pentagonal ring structure containing at least two nitrogen atoms to a hexagonal pyridine type of fragment via a direct carbon-carbon linkage.L is a neutral donor ligand; the typical example includes carbonyl, pyridine, phosphine, arsine and isocyanide; two neutral L's can also combine to produce the so-called chelating ligand such as 2,2′-bipyridine, 1,10-phenanthroline and N-heterocyclic carbene (NHC) ligand, or bidentate phosphorous ligands such as 1,2-bis(diphenylphosphino)ethane, 1,2-bis(diphenylphosphino)benzene.L can occupy either cis or trans orientation.When L occupies the trans position, the preferred structure contains both the hexagonal fragment of N^N as well as its pentagonal fragment located at the trans position respect to their counterparts of the second N^N chromophore.When L occupies the cis position, the preferred structure consists of the pentagonal unit of N^N chromophores residing opposite to the L.X,1 X2 and X3 independently are C or N;when X2 is N, R1 is omitted,when X3 is N, R2 is omitted,R1 is H, C1-C8 alkyl, C1-C8 substituted phenyl or C1-C4 perfluoroalkyl,R2 is H, F or cyano substituent,X4 is either C or N;X4 may locate at any position of the hexagonal ring, when X4 is N and R3 and R4 are not linked to X4,R3 is H, methyl or C1-C3 small alkyl, R4 is H, methyl or C1-C3 small alkyl, or R3 and R4 together form an additional conjugated unit with structure