The Design and Synthesis of Luminescent Iridium and Platinum Complexes featuring Bi-, Tri- and Tetra-dentate Ligands

Abstract

Luminescent transition metal complexes have a broad range of applications from display technologies and lighting to bio-imaging. A total of 85 iridium(III) and platinum(II) complexes featuring bidentate, tridentate and tetradentate ligands have been synthesized in this work with the aims of: (i) developing efficient emitters for potential incorporation into light-emitting electrochemical cells (LECs) and (ii) contributing novel design structures to the field of coordination photochemistry.

Chapter 2 focuses on Ir(III) complexes of the type [Ir(C^N)2(N^N)]PF6 which feature an N^C-cyclometalating ligand based on 2-phenylpyridine (ppyH) and an N^N ligand based on a bipyridine (bpy), pyrazolo[3,4-b]pyridine (pp), or 7-azaindole (az). Colour tuning of emission from max = 450 nm to 677 nm in solution was achieved by variation of both ligands. Impressive quantum yields of 53-57% were obtained by addition of mesityl and difluorophenyl groups to the periphery of the C^N ligand.

Chapter 3 describes the synthesis of cationic Ir(III) complexes bearing tridentate N^C^N ligands in combination with bpy derivatives, phenanthroline, pp- or az-based N^N ligands. Metathesis of the chloride ligand to phenylacetylide or cyanide red- and blue shifted the emission, respectively, by approximately 40-100 nm (1630-3200 cm‒1) with a marginal increase in quantum yield (φPL ≤ 6%).

In Chapter 4, platinum(II) and iridium(III) complexes bearing para-anisidine-linked tetradentate ligands are reported. The emission maxima of cyclometalated complexes of the type [Pt(N^N^N^C)]PF6 and Ir(N^N^N^C)Cl2 were blue shifted by 23-93 nm (504-3020 cm‒1) compared to their non-cyclometalated N^N^N^N-based counterparts. Metathesis of the axial chloride(s) in Ir complexes with cyanide and phenylacetylene induced a > 100 nm (> 2300 cm‒1) blue shift in emission with a negligible effect on quantum yield (φPL ≤ 6%).

Finally, in Chapter 5, di-iridium and di-platinum complexes containing para-anisidine-linked bis- bidentate N^N–N^N or bis-tridentate N^C^N–N^C^N bridging ligands were synthesized, where N^N = bpy or pp and N^C^N = dipyridylbenzene (φPL ≤ 17%). Addition of a second metal centre in the bis-tridentate series lowered quantum yield and red shifted emission. The mixed Ir(III)-Pt(II) complex was only emissive at low temperature. Metathesis of the Pt(N^C^N)Cl-type complex with phenylacetylene raised the quantum yield and marginally blue shifted emission whereas a larger red shift was seen in the analogous cyanide-containing Pt complex.