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

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
(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 because of the bulkiness of their side chains (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 applications
in chiroptical phosphorescent materials.