Stereospecific Synthesis of Tris-heteroleptic Tris-cyclometalated Iridium(III) Complexes via Different Heteroleptic Halogen-Bridged Iridium(III) Dimers and Their Photophysical Properties.

Herein, we report on the stereospecific synthesis of two single isomers of tris-heteroleptic tris-cyclometalated iridium(III) (Ir(III)) complexes composed of three different nonsymmetric cyclometalating ligands via heteroleptic halogen-bridged Ir dimers [Ir(tpy)(Fppy)(μ-Br)] 17b and [Ir(mpiq)(Fppy)(μ-Br)] 27b (tpyH: (2-(4'-tolyl)pyridine) and FppyH: (2-(4',6'-difluorophenyl)pyridine), and mpiqH: (1-(4'-methylphenyl)isoquinoline)) prepared by Zn-promoted degradation of Ir(tpy)(Fppy) 21 and Ir(mpiq)(Fppy) 26, as reported by us. Subsequently, 17b and 27b were converted to the tris-heteroleptic tris-cyclometalated Ir complexes Ir(tpy)(Fppy)(mpiq) 25 consisting of tpy, Fppy, 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.