Controlling Phosphorescence Color and Quantum Yields in Cationic Iridium Complexes: A Combined Experimental and Theoretical Study

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• 作者：Filippo De Angelis ; Simona Fantacci ; Nicholas Evans ; Cedric Klein ; Shaik M. Zakeeruddin ; Jacques-E. Moser ; Kuppuswamy Kalyanasundaram ; Henk J. Bolink ; M. Grä ; tzel ; Mohammed K. Nazeeruddin
• 刊名：Inorganic Chemistry
• 出版年：2007
• 出版时间：July 23, 2007
• 年：2007
• 卷：46
• 期：15
• 页码：5989 - 6001
• 全文大小：317K
• 年卷期：v.46,no.15(July 23, 2007)
• ISSN：1520-510X

文摘

We report a combined experimental and theoretical study on cationic Ir(III) complexes for OLED applications anddescribe a strategy to tune the phosphorescence wavelength and to enhance the emission quantum yields for thisclass of compounds. This is achieved by modulating the electronic structure and the excited states of the complexesby selective ligand functionalization. In particular, we report the synthesis, electrochemical characterization, andphotophysical properties of a new cationic Ir(III) complex, [Ir(2,4-difluorophenylpyridine)₂(4,4'-dimethylamino-2,2'-bipyridine)](PF₆) (N969), and compare the results with those reported for the analogous [Ir(2-phenylpyridine)₂(4,4'-dimethylamino-2,2'-bipyridine)](PF₆) (N926) and for the prototype [Ir(2-phenylpyridine)₂(4,4'-tert-butyl-2,2'-bipyridine)](PF₆) complex, hereafter labeled N925. The three complexes allow us to explore the (C^d.gif">N) and (N^d.gif">N) ligandfunctionalization: considering N925 as a reference, we investigate in N926 the effect of electron-releasing substituentson the bipyridine ligand, while in N969, we investigate the combined effect of electron-releasing substituents on thebipyridine ligand and the effect of electron-withdrawing substituents on the phenylpyridine ligands. For N969 weobtain blue-green emission at 463 nm with unprecedented high quantum yield of 85% in acetonitrile solution atroom temperature. To gain insight into the factors responsible for the emission color change and the differentquantum yields, we perform DFT and TDDFT calculations on the ground and excited states of the three complexes,characterizing the excited-state geometries and including solvation effects on the calculation of the excited states.This computational procedure allows us to provide a detailed assignment of the excited states involved in theabsorption and emission processes and to rationalize the factors determining the efficiency of radiative andnonradiative deactivation pathways in the investigated complexes. This work represents an example of electronicstructure-driven tuning of the excited-state properties, thus opening the way to a combined theoretical and experimentalstrategy for the design of new iridium(III) phosphors with specific target characteristics.