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  4. Acid-Induced Degradation of Phosphorescent Dopants for OLEDs and Its Application to the Synthesis of Tris-heteroleptic Iridium(III) Bis-cyclometalated Complexes
 
research article

Acid-Induced Degradation of Phosphorescent Dopants for OLEDs and Its Application to the Synthesis of Tris-heteroleptic Iridium(III) Bis-cyclometalated Complexes

Baranoff, Etienne  
•
Curchod, Basile F. E.  
•
Frey, Julien  
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2012
Inorganic Chemistry

Investigations of blue phosphorescent organic light emitting diodes (OLEDs) based on [Ir(2-(2,4-difluorophenyl)pyridine)(2)(picolinate)] (FIrPic) have pointed to the cleavage of the picolinate as a possible reason for device instability. We reproduced the loss of picolinate and acetylacetonate ancillary ligands in solution by the addition of Brønsted or Lewis acids. When hydrochloric acid is added to a solution of a [Ir(C(∧)N)(2)(X(∧)O)] complex (C(∧)N = 2-phenylpyridine (ppy) or 2-(2,4-difluorophenyl)pyridine (diFppy) and X(∧)O = picolinate (pic) or acetylacetonate (acac)), the cleavage of the ancillary ligand results in the direct formation of the chloro-bridged iridium(III) dimer [{Ir(C(∧)N)(2)(μ-Cl)}(2)]. When triflic acid or boron trifluoride are used, a source of chloride (here tetrabutylammonium chloride) is added to obtain the same chloro-bridged iridium(III) dimer. Then, we advantageously used this degradation reaction for the efficient synthesis of tris-heteroleptic cyclometalated iridium(III) complexes [Ir(C(∧)N(1))(C(∧)N(2))(L)], a family of cyclometalated complexes otherwise challenging to prepare. We used an iridium(I) complex, [{Ir(COD)(μ-Cl)}(2)], and a stoichiometric amount of two different C(∧)N ligands (C(∧)N(1) = ppy; C(∧)N(2) = diFppy) as starting materials for the swift preparation of the chloro-bridged iridium(III) dimers. After reacting the mixture with acetylacetonate and subsequent purification, the tris-heteroleptic complex [Ir(ppy)(diFppy)(acac)] could be isolated with good yield from the crude containing as well the bis-heteroleptic complexes [Ir(ppy)(2)(acac)] and [Ir(diFppy)(2)(acac)]. Reaction of the tris-heteroleptic acac complex with hydrochloric acid gives pure heteroleptic chloro-bridged iridium dimer [{Ir(ppy)(diFppy)(μ-Cl)}(2)], which can be used as starting material for the preparation of a new tris-heteroleptic iridium(III) complex based on these two C(∧)N ligands. Finally, we use DFT/LR-TDDFT to rationalize the impact of the two different C(∧)N ligands on the observed photophysical and electrochemical properties.

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Type
research article
DOI
10.1021/ic202162q
Web of Science ID

WOS:000298712000032

Author(s)
Baranoff, Etienne  
Curchod, Basile F. E.  
Frey, Julien  
Scopelliti, Rosario  
Kessler, Florian  
Tavernelli, Ivano  
Rothlisberger, Ursula  
Grätzel, Michael  
Nazeeruddin, Md Khaja  
Date Issued

2012

Published in
Inorganic Chemistry
Volume

51

Start page

215

End page

224

Subjects

Light-Emitting-Diodes

•

Ortho-Metalated Complexes

•

Noncovalent Interactions

•

Thermochemical Kinetics

•

Molecular Calculations

•

Density Functionals

•

Blue

•

Ligands

•

Devices

•

Ir(Iii)

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
LCBC  
LPI  
Available on Infoscience
January 6, 2012
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/76397
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