Phosphorescent Chiral Cationic Binuclear Iridium(III) Complexes: Boosting the Circularly Polarized Luminescence Brightness

We report the synthesis and characterization of two chiral binuclear iridium(III) complexes (Lambda Lambda and Delta Delta) prepared from enantiopure building blocks [mu-Cl2(Delta-Ir(C<^>N)2)2] and [mu-Cl2(Lambda-Ir(C<^>N)2)2]. These building blocks have been obtained by chiral preparative high-performance liquid chromatography of the neutral iridium(III) complex Irpiv (piv = 2,2,6,6-tetramethylheptane-3,5-dionate) followed by selective degradation of the ancillary ligand. For comparison purposes, we also synthesized a monomer (IrL1 ) and a dimer (Ir2L2 , mixture). All the complexes exhibit similar emission properties, emitting in the orange-red region of the spectra with a good photoluminescence quantum yield (lambda max = 610-625 nm, Phi similar to 25%, tau similar to 800-900 ns). However, the Lambda Lambda and Delta Delta complexes are optically active, indicating that no isomerization occurred during the different synthetic steps, as evidenced by both the circular dichroism spectra and their circularly polarized luminescence (CPL). The capital gain of the dimers (Ir2L2 , Lambda Lambda, and Delta Delta) is a 4-fold brightness (B 380 = epsilon 380 nm x Phi) compared to the monomer (IrL1 ) and the CPL brightness (B CPL = B 380 x g lum/2) of the binuclear complexes being among the highest reported to date for chiral iridium(III) complexes.