Analytical Sciences

Electrochemical and Phosphorescent Properties of New Ir(III) Complexes Coordinated by Various Bipyridine Derivatives

Naokazu YOSHIKAWA,* Jun SAKAMOTO,** Takeko MATSUMURA-INOUE,** Hiroshi TAKASHIMA,* Keiichi TSUKAHARA,* Nobuko KANEHISA,*** and Yasushi KAI***

*Department of Chemistry, Faculty of Science, Nara Women’s University, Nara, 630-8506, Japan
**Department of Chemistry, Nara University of Education, Takabatake-cho, Nara 630-8528, Japan
***Department of Applied Chemistry, Graduate School of Engineering Osaka University, Yamada-Oka 2-1, Suita, Osaka, 565-0871, Japan

Four useful polypyridine iridium(III) complexes in the form of [IrCl₂L₂]⁺ were prepared and their spectroscopic and electrochemical properties as well as X-ray crystallography were investigated. The ligands used were L = 2,2′-bipyridine, 4,4′-dimethyl-2,2′-bipyridine, 4,4′-diphenyl-2,2′-bipyridine, 1,10-phenanthroline, 4,7-diphenyl-1,10-phenanthroline, and 2,2′-biquinoline. Synthetic methods were developed by a sequential ligand-replacement, which occurred in the reaction vessel using a microwave oven. All complexes showed that LUMOs are based on the π-system contribution of the polypyridine ligand for [IrCl₂(bpy)₂]⁺, [IrCl₂(dmbpy)₂]⁺, [IrCl₂(dpbpy)₂]⁺, [IrCl₂(phen)₂]⁺, [IrCl₂(dpphen)₂]⁺ and [IrCl₂(bqn)₂]⁺. The HOMOs are also localized on the polypyridine ligand in the iridium complexes. It was found that [IrCl₂L₂]⁺ emits intense phosphorescence at room temperature. In particular, the use of dpbpy as ancillary ligands extends the lifetime (660 ns) of the ³(π-π^*) excited states of Ir(III) polypyridine complexes. The complex [IrCl₂(bqn)₂]⁺ with electron acceptor substituents shows a large red-shift to 622 nm. It is noticed that iridium polypyridine complexes show intense emissions at various colors, such as yellow for [IrCl₂(dmbpy)₂]⁺ and red for [IrCl₂(bqn)₂]⁺, which can be applied to photosensitizers. The spectroscopic and electrochemical details are also reported herein.

J-STAGE: View this article in J-STAGE