Stereospecific Synthesis of Tris-heteroleptic Tris-cyclometalated Iridium(III) Complexes via Different Heteroleptic Halogen-Bridged Iridium(III) Dimers and Their Photophysical Properties Yuichi Tamura, † Yosuke Hisamatsu, † Ayami Kazama, † Kenji Yoza, ‡ Kyouhei Sato, § Reiko Kuroda, § and Shin Aoki* ,†,∥,⊥ † Faculty of Pharmaceutical Sciences, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan ‡ Bruker AXS K.K., 3-9 Moriya-cho, Yokohama, Kanagawa 221-0022, Japan § Research Institute for Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan ∥ Division of Medical-Science-Engineering Cooperation, Research Institute for Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan ⊥ Imaging Frontier Center, Research Institute for Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan * S Supporting Information ABSTRACT: Herein, we report on the stereospecific syn- thesis of two single isomers of tris-heteroleptic tris-cyclo- metalated iridium(III) (Ir(III)) complexes composed of three different nonsymmetric cyclometalating ligands via hetero- leptic halogen-bridged Ir dimers [Ir(tpy)(F 2 ppy)(μ-Br)] 2 17b and [Ir(mpiq)(F 2 ppy)(μ-Br)] 2 27b (tpyH: (2-(4′-tolyl)pyri- dine) and F 2 ppyH: (2-(4′,6′-difluorophenyl)pyridine), and mpiqH: (1-(4′-methylphenyl)isoquinoline)) prepared by Zn 2+ -promoted degradation of Ir(tpy) 2 (F 2 ppy) 21 and Ir- (mpiq) 2 (F 2 ppy) 26, as reported by us. Subsequently, 17b and 27b were converted to the tris-heteroleptic tris-cyclometalated Ir complexes Ir(tpy)(F 2 ppy)(mpiq) 25 consisting of tpy, F 2 ppy, and mpiq, as confirmed by spectroscopic data and X-ray crystal structure analysis. The first important point in this work is the selective synthesis of specific isomers among eight possible stereoisomers of Ir complexes having the same combination of three cyclometalating ligands. Namely, two meridional forms of 25 were synthesized and isolated. The second finding is that the different stereoisomers of 25 have different stability. Finally, different stereoisomers exhibit different emission spectra. Namely, one of its stereoisomers 25a exhibits a single broad emission from ca. 550 nm to ca. 650 nm (orange emission), while stereoisomer 25c emits dual emission at ca. 509 nm and ca. 600 nm (pale pink emission), as supported by time-dependent density functional theory calculation. To the best of our knowledge, this is the first report of the selective and efficient synthesis of different stereoisomers of tris-heteroleptic tris-cyclometalated Ir(III) complexes that have different stabilities and different photophysical properties. ■ INTRODUCTION Cyclometalated Ir(III) complexes as phosphorescence emitters have gained widespread interest as attractive candidates for use in organic light emitting diodes (OLEDs), 1 bioimaging probes, 2 oxygen sensors, 3 anticancer agents, 4 photoredox catalysts, 5 pH sensors, 6 and so on, 7 because of their remarkable optoelectronic properties. 8 To date, numerous examples of Ir complexes have been prepared and most of them can be categorized as IrL 3 , IrL 2 L′, IrL 2 A, and IL 2 A′, as shown in Chart 1, where L and L′ are different cyclometalating ligands that chelate to an Ir ion via carbon and hetero atoms, A depicts a symmetric ancillary ligand that binds to Ir via two hetero atoms, and A′ represents a nonsymmetric ancillary ligand. Tris-heteroleptic Ir complexes containing an Ir ion with three different cyclometalating ligands (IrLL′L″) or a combination of two different cyclometalating ligands and one ancillary ligand (IrLL′A or IrLL′A′) represent new classes of highly function- alized Ir complexes, which may open new avenues for the fine- tuning of their photochemical and electrochemical properties and could fill a function gap between a series of the homoleptic and bis-heteroleptic Ir complexes. Representative synthetic methods of IrLL′A and IrLL′A′ are shown in Chart 2, in which A is a symmetrical ancillary ligand such as acetylacetone (acacH), bipyridine (bpy), and 1,10- Received: February 5, 2018 Article pubs.acs.org/IC Cite This: Inorg. Chem. XXXX, XXX, XXX-XXX © XXXX American Chemical Society A DOI: 10.1021/acs.inorgchem.8b00323 Inorg. Chem. XXXX, XXX, XXX−XXX