Syntheses and properties of emissive iridium(III) complexes with tridentate benzimidazole derivatives

Tomona Yutaka, Shinya Obara, Satoshi Ogawa, Koichi Nozaki, Noriaki Ikeda, Takeshi Ohno, Youichi Ishii, Ken Sakai, Masa Aki Haga

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118 Citations (Scopus)

Abstract

A series of novel emissive Ir(III) complexes having the coordination environments of [Ir(N∧N∧N)2]3+, [Ir(N∧N∧N)-(N∧N)Cl]2+, and [Ir(N∧N∧N) (N∧C∧N)]2+ with 2,6-bis(1-methyl-benzimidazol-2-yl)pyridine (L1, N∧N∧N), 1,3-bis-(1-methyl-benzimidazol-2-yl)benzene (L2H, N∧C∧N), 4′-(4-methylphenyl)-2,2′:6′,2″- terpyridine (ttpy, N∧N∧N), and 2,2′-bipyridine (bpy, N∧N) have been synthesized and their photophysical and electrochemical properties studied. The Ir(III) complexes exhibited phosphorescent emissions in the 500-600 nm region, with lifetimes ranging from approximately 1-10 μs at 295 K. Analysis of the 0-0 energies and the redox potentials indicated that the lowest excited state of [Ir(L1)(L2)]2+ possessed the highest contribution of 3MLCT (MLCT = metal-to-ligand charge transfer) among the Ir(III) complexes, reflecting the σ-donating ability of the tridentate ligand, ttpy < L1 < L2. The emission quantum yields (Φ) of the Ir(III) complexes ranged from 0.037 to 0.19, and the highest Φ value (0.19) was obtained for [Ir(L1)(bpy)Cl]2+. Radiative rate constants (k r) were 1.2 × 104 s-1 for [Ir(ttpy) 2]3+, 3.7 × 104 s-1 for [Ir(L1)(bpy)-Cl]2+, 3.8 × 104 s-1 for [Ir(ttpy)(bpy)Cl]2+, 3.9 × 104 s-1 for [Ir(L1)2]3+, and 6.6 × 104 s-1 for [Ir(L1)(L2)]2+. The highest radiative rate for [Ir(L1)(L2)] 2+ with the highest contribution of 3MLCT could be explained in terms of the singlet-triplet mixing induced by spin-orbit coupling of 5d electrons in the MLCT electronic configurations.

Original languageEnglish
Pages (from-to)4737-4746
Number of pages10
JournalInorganic Chemistry
Volume44
Issue number13
DOIs
Publication statusPublished - Jun 27 2005

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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