The synthesis and luminescence properties of platinum, palladium and iridium complexes featuring multidentate ligands

Abstract

Luminescent metal complexes have seen great success in many applications from bio-sensing to display technology and lighting. A range of different Pt, Pd and Ir complexes
featuring multidentate ligands have been synthesised in this work with the aim of incorporation into organic light emitting diodes (OLEDs).
Chapter 2 focuses on Pt complexes containing bidentate 1,2,4-triazole ligands. Homoleptic complexes exhibit red emission that is concentration-dependent, showing excimeric
emission at higher concentrations. Impressive quantum yield (φ) values ranging from 21 to 48 % have been obtained in degassed solution. Consequently, both solution-processed and
vacuum thermally evaporated devices of these complexes were fabricated and a maximum EQE of 14.9 % was obtained for a thermally evaporated device.
Chapter 3 describes the synthesis and photophysical properties of IrIII complexes featuring tridentate N^C^N ligands in combination with 1,2,4-triazole ligands of bidentate and tridentate denticity. Some isoelectronic PtIV analogues were also synthesised for comparison. The PtIV complexes display superior photophysical properties in comparison to the Ir complexes. Indeed, the Pt complex containing dipyridylbenzene (dpyb) as the N^C^N ligand in combination with a bidentate 1,2,4-triazole ligand has a φ of 5.9 % and a lifetime of 3.1 µs. On increasing the denticity of the triazole ligand from bidentate to tridentate in a bis-tridentate Pt complex, an improved φ of 28 % and a lifetime of 11 µs were obtained.
In Chapter 4, Pt and Pd analogues containing C^N^N^C ligands were synthesised and probed for their excimeric emission. Increased complex rigidity was observed for these compounds due to the incorporation of tetradentate ligands about the metal centre. The Pt compounds generally displayed more impressive photophysical properties compared to their Pd analogues, but a Pd complex containing a thiophene tetradentate ligand was incorporated into a solution-processed OLED to give a respectable EQE of 3.17 %.
Finally, in Chapter 5 the foundations for future work to achieve highly efficient NIR OLEDs were laid via the synthesis of dinuclear complexes containing Pt(N^C^N) units rigidly linked by a xanthene core in a face-to-face conformation. These complexes displayed visible and
NIR emission with high efficiencies in both solution (φ = 5-35 %) and in films (φ up to 57 %). The NIR emission emanates from excimer-like excited states in each case, probably involving a varying mixture of face-to-face intra- and intermolecular interactions.