The synthesis, structural characterisation, and photophysical properties of platinum(IV) complexes with tri- or tetra-dentate ligands

Abstract

The work in this thesis aims to develop Pt(IV) complexes incorporating tridentate and tetradentate ligands and to explore their photophysical properties.

The synthesis of Pt(IV) complexes featuring NCN- and NNC-coordinating tridentate ligands is detailed in Chapters 2 and 3. Complexes of the type 3 + 2 + 1 were prepared, which incorporate one cyclometallating tridentate ligand, one bidentate ligand (NC – cyclometallating or NN – coordinating), and a monodentate chloride, as well as the first examples of bis-tridentate Pt(IV) complexes. The bis-cyclometallated complexes featuring an NNC ligand are luminescent in degassed acetonitrile at room temperature with quantum yields ranging from 0.4% to 4%.

Chapter 4 explores further examples of [Pt(NNC)(NC)Cl]+ complexes that incorporate a phenyl substituent at the 6-position of the NNC lateral pyridine ring. While their photophysical properties in solution were similar to those of their unsubstituted counterparts, significant enhancements in quantum yield were observed when embedded in PMMA films, likely due to a π – π interaction between the phenyl substituent on the NNC ligand and the pyridine ring of the NC ligand.

In Chapter 5 the development of dinuclear complexes featuring rigid, ditopic bis-tridentate pyrimidine-bridged CNN-NNC ligands is described. The reactions of these ligands with KPtCl yielded mononuclear Pt(II) complexes. However, further oxidation to Pt(IV), followed by reaction with additional KPtCl, facilitated the formation of dinuclear Pt(II)/Pt(IV) complexes. These were further oxidised to yield dinuclear Pt(IV) complexes. A trace amount of a dinuclear complex of the type [CNN-NNCPt(ppy)Cl] was successfully isolated, and found to be luminescent with a quantum yield of 1.6% and a lifetime of 13 μs.

Chapter 6 focuses on the synthesis of tetradentate NCCN ligands, incorporating pyridine or quinoline heterocycles and substituted phenyl cyclometallating rings, and their complexation with platinum. Mixtures of Pt(II) and Pt(IV) complexes were formed, and in one instance a dimeric Pt(III) complex. The Pt(IV) complexes were only emissive at 77 K, but the Pt(II) complexes were luminescent also at room temperature, with quantum yields reaching up to 67% in CHCl solution.