Impact of the number of o-carboranyl ligands on the photophysical and electroluminescent properties of iridium(III) cyclometalates

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A series of iridium(III) cyclometalates with mono-, bis-, and tris-o-carboranyl ligands, fac-[m-(2-MeCB)ppy](n)Ir(ppy)(3-n) (n = 13, m = 5 (3a5a); m = 4 (3b5b); 2-MeCB = 2-methyl-o-carboran-1-yl; ppy = 2-phenylpyridinato-C-2,N), was prepared to investigate the impact of the number of o-carboranyl ligands on the photophysical and electroluminescent properties. X-ray diffraction analysis of 3b5b revealed that the carboranyl CC bond distances remained nearly unchanged with different numbers of carboranyl ligands. While the phosphorescence wavelengths of 3a5a and 3b5b were blue-shifted or red-shifted with respect to that of fac-Ir(ppy)3 (6), respectively, both series underwent gradual hypsochromic shifts as the number of carboranyl ligands was increased. All of the complexes exhibited moderate to high phosphorescence quantum efficiencies in toluene with a slightly higher efficiency for the 5-substituted 3a5a (Phi(PL) = 0.430.98) than for the 4-substituted 3b5b (Phi(PL) = 0.420.92). In particular, the quantum efficiency increased as the number of carboranyl ligands increased. Solution-processed green phosphorescent organic light-emitting diodes (PhOLEDs) incorporating the 5-substituted complexes (3a5a) as emitters exhibited a similar level of high performance, of which the best performance was observed for devices based on 4a. Furthermore, vacuum-deposited devices were successfully fabricated with heteroleptic mono- and bis-carboranyl complexes, 3a and 4a. The resulting devices showed excellent performance, which was improved by ca. 40% compared to those of the solution-processed devices. The devices based on 4a also displayed a performance that was superior to those of the devices based on 3a (max. CE = 45.8 cd A(-1); PE = 35.4 lm W-1; EQE = 15.1% for 4a at 7 wt% Ir).
Publisher
ROYAL SOC CHEMISTRY
Issue Date
2017-02
Language
English
Article Type
Article
Keywords

LIGHT-EMITTING DEVICES; MOLECULAR-ORBITAL METHODS; C-C DISTANCE; ELECTROPHOSPHORESCENT DEVICES; PHOSPHORESCENCE EFFICIENCY; RED PHOSPHORESCENCE; POLYHEDRAL BORANES; IR(III) COMPLEXES; RECENT PROGRESS; CHARGE-TRANSFER

Citation

JOURNAL OF MATERIALS CHEMISTRY C, v.5, no.12, pp.3024 - 3034

ISSN
2050-7526
DOI
10.1039/c7tc00247e
URI
http://hdl.handle.net/10203/223445
Appears in Collection
EE-Journal Papers(저널논문)
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