Substituent effect on the electroluminescence efficiency of amidinate-ligated bis(pyridylphenyl) iridium( iii ) complexes
This paper reports the synthesis, structure, and photophysical and electrophosphorescence properties of heteroleptic amidinate/bis(pyridylphenyl) iridium( iii ) complexes having different substituents on the nitrogen atoms of the amidinate ancillary ligands. The reaction of bis(pyridylphenyl) iridiu...
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Published in | Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 2; no. 27; pp. 5317 - 5326 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
21.07.2014
|
Subjects | |
Online Access | Get full text |
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Summary: | This paper reports the synthesis, structure, and photophysical and electrophosphorescence properties of heteroleptic amidinate/bis(pyridylphenyl) iridium(
iii
) complexes having different substituents on the nitrogen atoms of the amidinate ancillary ligands. The reaction of bis(pyridylphenyl) iridium(
iii
) chloride [(ppy)
2
Ir(μ-Cl)]
2
with the lithium salt of various amidinate ligands Li{(NR)(NR′)CPh} at 80 °C gave in 60–80% yields the corresponding heteroleptic bis(pyridylphenyl)/amidinate iridium(
iii
) complexes having a general formula [(ppy)
2
Ir{(NR)(NR′)CPh}], where R = R′ =
i
Pr (
1
), R = R′ =
t
-Bu (
2
), R = Et, R′ =
t
-Bu (
3
), and R = Et, R′ = (CH
2
)
3
N(CH
3
)
2
(
4
). These heteroleptic iridium(
iii
) complexes exhibited bright yellowish-green phosphorescence emission with moderate photoluminescence (PL) quantum yields (
Φ
PL
= 0.16–0.34) and short phosphorescence lifetimes of 0.98–1.18 μs in toluene solution at room temperature. Organic light-emitting diodes (OLEDs) were fabricated by the use of these complexes as phosphorescent dopants in various concentrations (
x
= 5–100 wt%) in the 4,4′-
N
,
N
′-dicarbazolylbiphenyl (CBP) host. Because of the steric hindrance of the amidinate ligands, no significant intermolecular interaction was observed in these complexes, thus leading to the reduction of self-quenching and triple–triplet annihilation at high currents/luminance. A significant influence of the substituents in the amidinate ligands on the electroluminescence efficiency was observed. Among these complexes, complex (
2
), which contains the bulky
t
-butyl group on the amidinate nitrogen atoms, showed the highest current efficiency (
η
c
: up to 116 cd A
−1
), power efficiency (
η
p
: up to 72.2 lm W
−1
) and external quantum efficiency (
η
ext
; up to 16.3%). |
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Bibliography: | ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 |
ISSN: | 2050-7526 2050-7534 |
DOI: | 10.1039/C3TC32553A |