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Ionic Iridium(III) Complexes with Bulky Side Groups for Use in Light Emitting Cells: Reduction of Concentration Quenching
Author(s) -
Rothe Carsten,
Chiang ChienJung,
Jankus Vygintas,
Abdullah Khalid,
Zeng Xianshun,
Jitchati Rukkiat,
Batsanov Andrei S.,
Bryce Martin R.,
Monkman Andrew P.
Publication year - 2009
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.200801767
Subject(s) - iridium , quenching (fluorescence) , ligand (biochemistry) , crystallography , intermolecular force , materials science , excited state , ionic bonding , oled , phosphorescence , photochemistry , chemistry , fluorescence , molecule , physics , ion , layer (electronics) , nanotechnology , catalysis , atomic physics , biochemistry , receptor , organic chemistry , quantum mechanics
Here, the photophysics and performance of single‐layer light emitting cells (LECs) based on a series of ionic cyclometalated Ir(III) complexes of formulae $\left[ {{\rm Ir}\left( {{\rm ppy}} \right)_{\rm 2} \left( {{\rm bpy}} \right)} \right]^ + {\rm PF}_{\rm 6}^ -$ and $\left[ {{\rm Ir}\left( {{\rm ppy}} \right)_{\rm 2} \left( {{\rm phen}} \right)} \right]^ + {\rm PF}_{\rm 6}^ -$ where ppy, bpy, and phen are 2‐phenylpyridine, substituted bipyridine and substituted phenanthroline ligands, respectively, are reported. Substitution at the NˆN ligand has little effect on the emitting metal‐ligand to ligand charge‐transfer (MLLCT) states and functionalization at this site of the complex leads to only modest changes in emission color. For the more bulky complexes the increase in intermolecular separation leads to reduced exciton migration, which in turn, by suppressing concentration quenching, significantly increases the lifetime of the excited state. On the other hand, the larger intermolecular separation induced by bulky ligands reduces the charge carrier mobility of the materials, which means that higher bias fields are needed to drive the diodes. A brightness of ca. 1000 cd m −2 at 3 V is obtained for complex 5, which demonstrates a beneficial effect of bulky substituents.