Deep-Red Circularly Polarized Phosphorescence from Binuclear Cyclometalated Platinum(II) Complexes with 2-(Benzo[ <i>b</i> ]thiophen-2-yl)pyridine Ligands via a Planar Chirality Strategy

Circularly polarized phosphorescent cyclometalated platinum(II) complexes have drawn increasing research interest for chiral-related applications owing to their rich photophysical properties. The formation of the binuclear cyclometalated platinum(II) complexes through intramolecular Pt-Pt interaction provides an approach for realizing planar chirality. In this contribution, we developed a series of Pt-Pt interaction-involved binuclear cyclometalated platinum(II) complexes by incorporating 2-(benzo[<i>b</i>]thiophen-2-yl)pyridine as the cyclometalating ligand and chiral thiazolidine-2-thione-type bridging ligands. Highly efficient diastereoselectivity could be induced by point chirality from the chiral bridging ligand to give rise to chiral pure enantiomers ((<i>R</i>,<i>S</i>,<i>R</i>)-<b>PtI</b>, (<i>S</i>,<i>R</i>,<i>S</i>)-<b>PtI</b>, (<i>R</i>,<i>S</i>,<i>R</i>)-<b>PtII</b>, and (<i>S</i>,<i>R</i>,<i>S</i>)-<b>PtII</b>). These chiral platinum(II) complexes exhibit bright, deep-red circularly polarized room-temperature phosphorescence at around 630 nm with photoluminescence quantum yields as high as 0.90, which is attributed to the presence of the metal-metal-to-ligand charge transfer through strong intramolecular Pt-Pt interactions. Moreover, the luminescence dissymmetry factors for these enantiomers in CH₂Cl₂ could be increased from 3.3/-3.7 × 10^-3 to 4.6/-4.9 × 10^-3 by replacing the isopropyl group with the phenyl one in chiral bridging ligands. The excellent photophysical properties of the chiral platinum(II) complexes imply that they will show great potential in optoelectronic applications.