Manipulation of Phosphorescence Efficiency of Cyclometalated Iridium Complexes by Substituted o-Carboranes

Title
Manipulation of Phosphorescence Efficiency of Cyclometalated Iridium Complexes by Substituted o-Carboranes
Authors
이상욱
Keywords
Carboranes; Iridium; Organic light-emitting diodes; Photophysics; Quantum efficiency
Issue Date
2015-01
Publisher
WILEY-V C H VERLAG GMBH
Citation
CHEMISTRY - A EUROPEAN JOURNAL, v. 21, NO 5, Page. 2052-2061
Abstract
A series of [(C^N)2Ir(acac)] complexes [{5-(2-R-CB)ppy}2Ir(acac)] (3 a–3 g; acac=acetylacetonate, CB=o-carboran-1-yl, ppy=2-phenylpyridine; R=H (3 a), Me (3 b), iPr (3 c), iBu (3 d), Ph (3 e), CF3C6H4 (3 f), C6F5 (3 g)) with various 2-R-substituted o-carboranes at the 5-position in the phenyl ring of the ppy ligand were prepared. X-ray diffraction studies revealed that the carboranyl C[BOND]C bond length increases with increasing steric and electron-withdrawing effects from the 2-R substituents. Although the absorption and emission wavelengths of the complexes are almost invariant to the change of 2-R group, the phosphorescence quantum efficiency varies from highly emissive (ΦPL≈0.80 for R=H, alkyl) to poorly emissive (R=aryl) depending on the 2-R group and the polarity of the medium. Theoretical studies suggest that 1) the almost nonemissive nature of the 2-aryl-substituted complexes is mainly attributable to the large contribution to the LUMO in the S1 excited state from an o-carborane unit and 2) the variation in the C[BOND]C bond length between the S0 and T1 state structures increases with increasing steric (2-alkyl) and electronic effects (2-aryl) of the 2-R substituent and the polarity of the solvent. The solution-processed electroluminescence (EL) devices that incorporated 3 b and 3 d as emitters displayed higher performance than the device based on the parent [(ppy)2Ir(acac)] complex. Along with the high phosphorescence efficiency, the bulkiness of the 2-R-o-carborane unit is shown to play an important role in improving device performance.
URI
http://hdl.handle.net/20.500.11754/21106http://onlinelibrary.wiley.com/doi/10.1002/chem.201405433/abstract;jsessionid=761CCC6E2A8812A49A73DD77490DBF3F.f02t04?systemMessage=Pay+Per+View+on+Wiley+Online+Library+will+be+unavailable+on+Saturday+15th+April+from+12%3A00-09%3A00+EDT+for+essential+maintenance.++Apologies+for+the+inconvenience.
ISSN
1521-3765
DOI
http://dx.doi.org/10.1002/chem.201405433
Appears in Collections:
GRADUATE SCHOOL[S](대학원) > BIONANOTECHNOLOGY(바이오나노학과) > Articles
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