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)­(F₂ppy)­(μ-Br)]₂ <b>17b</b> and [Ir­(mpiq)­(F₂ppy)­(μ-Br)]₂ <b>27b</b> (tpyH: (2-(4′-tolyl)­pyri­dine) and F₂ppyH: (2-(4′,6′-di­fluoro­phenyl)­pyridine), and mpiqH: (1-(4′-methyl­phenyl)­iso­quinoline)) prepared by Zn²⁺-promoted degradation of Ir­(tpy)₂­(F₂ppy) <b>21</b> and Ir­(mpiq)₂­(F₂ppy) <b>26</b>, as reported by us. Subsequently, <b>17b</b> and <b>27b</b> were converted to the tris-heteroleptic tris-cyclometalated Ir complexes Ir­(tpy)­(F₂ppy)­(mpiq) <b>25</b> consisting of tpy, F₂ppy, 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 <b>25</b> were synthesized and isolated. The second finding is that the different stereoisomers of <b>25</b> have different stability. Finally, different stereoisomers exhibit different emission spectra. Namely, one of its stereoisomers <b>25a</b> exhibits a single broad emission from <i>ca</i>. 550 nm to <i>ca</i>. 650 nm (orange emission), while stereoisomer <b>25c</b> emits dual emission at <i>ca</i>. 509 nm and <i>ca</i>. 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