Enhancement of Photofunction of Phosphorescent Pt(II) Cyclometalated Complexes Driven by Substituents: Solid-state Luminescence and Circularly Polarized Luminescence.

Abstract

Ligand functionalization is an attractive strategy for enhancing the performance of metal-based phosphorescent emitters. Here we report the synthesis and characterization of cyclometalated Pt(II) complexes Pt3 and Pt4 containing organosilyl-substituted thpy (2-(2-thienyl)pyridine) ligands and compare their properties with those of Pt1 (no substituent) and Pt2 (organocarbon substituent). The photophysical characteristics of these molecules, including their absorption and phosphorescence spectra, phosphorescence quantum yield and lifetime, were investigated. The molecular structures were revealed by X-ray diffraction analysis. Under UV light irradiation, Pt2-Pt4 emitted intense orange phosphorescence in the solid state due to the bulkiness of their sidechain (up to ΦP: 0.49). Optically pure (‒)-(S)Si-Pt4 and (+)-(R)Si-Pt4 were prepared using the optically active ligands (+)-L4 and (‒)-L4, respectively. The chiroptical properties of (+)-(R)Si-Pt4, which has an asymmetric silicon atom, were investigated. Circular dichroism and circularly polarized luminescence measurements showed that these structural motifs are suitable for application in chiroptical phosphorescent materials.