Inhibition of Aggregation-Caused Quenching in "Half-Sandwich" Red-Phosphorescent Cyclometalated Platinum(II)...

Aggregation-caused quenching (ACQ) is a significant challenge encountered in luminescent square-planar Pt(II) complexes, especially in condensed phases such as neat or doped films. Herein, five red-emitting heteroleptic bis-bidentate cyclometalated Pt(II) complexes are described, supported by sterically encumbering "half-sandwich" β-ketoiminate or 2-picolinamide ancillary ligands. The electron-rich nature of the ancillary ligands promotes fast radiative decay, and the "half-sandwich" design places steric bulk directly over the metal center and inhibits ACQ. As a result, the photoluminescence color profiles and quantum yields of the complexes are largely preserved at different concentrations in doped films. All five presented complexes exhibit red phosphorescence with moderate Φ_PL up to 0.45, obtained in poly(methyl methacrylate) films at 2 wt%. These values gradually drop by only 0.06-0.12 when increasing the concentration to 5 and 10 wt%, with no significant changes in the photoluminescence emission profile observed. The structures of all five complexes were characterized by multinuclear NMR, with two of them by single-crystal X-ray diffraction (XRD). This work enriches the library of red-phosphorescent cyclometalated Pt(II) complexes, highlighting the effectiveness of "half-sandwich" ligand architectures in ACQ inhibition.