Diastereoselective Synthesis and Photophysical Properties of Bis-Cyclometalated Ir(III) Stereoisomers with Dual Stereocenters

Diastereoselective synthesis of bis-cyclometalated Ir(III) stereoisomers Delta/Lambda-[Ir((CN)-N-boolean AND)(2)(D-pro)] and Delta/Lambda-[Ir((CN)-N-<^>)2(L-pro)] (where (CN)-N-<^> is 2-phenylpyridine (Hppy), (4,6-difluorophenyl)pyridine (Hdfppy), and 2-phenylquinoline (Hpq) and pro is proline) with dual stereogenic centers at the metal and auxiliary ligand has been developed. The diastereomers Lambda-L and Lambda-D, and Lambda-L and Lambda-D exhibit distinguishable photophysical properties in both solution and the solid state. The thermodynamically stable diastereomers Lambda-[Ir(ppy),(L-pro)], Lambda-[Ir(dfppy)(2)(Lpro)], and Lambda-[Ir(pq)2(L-pro)] emit a green emission at 524 nm phi=3.5% and tau = 35 ns), a blue-green emission at 480 nm = tau 4.5% and tau = 59 ns), and a red emission at 588 nm (phi= 6.5% and = 200 ns) in DCM solution, respectively, which are blue -shifted accompanied by a large quantum yield and long lifetime relative to the corresponding unstable diastereomers Delta-[Ir(ppy)2(L-pro)] at 537 nm (phi= 2.3% and tau = 29 ns), Delta-[Ir(dfppy)2(L-pro)] at 489 nm ( phi= 2.8% and tau = 43 ns), and Lambda-[Ir(pq)2(L-pro)] at 591 nm (phi = 5.4% and tau = 192 ns). Similar cases were also observed in crystals, but the signals were significantly red -shifted with respect to those in solution. Single-crystal structural analyses show that the Delta-L and Lambda-D diastereomers exhibit larger interligand repulsion, and loose molecular packing with respect to the Delta-D and Lambda-L diastereomers, resulting in energy and photophysical property differences. In addition, the isomers with Delta and A configurations at the metal center exhibit positive and negative circularly polarized luminescence (CPL) signals, respectively, indicating that the effects of the chiral carbon atoms in pro ligands on CPL signals are negligible.