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Title: Multimetallic emitters for bioimaging and display applications
Author: Daniels, Ruth
ISNI:       0000 0004 7430 1156
Awarding Body: Northumbria University
Current Institution: Northumbria University
Date of Award: 2017
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The luminescent properties of transition metal complexes of heavy metals such as platinum(II) and irdium(III) are often highly luminescent and therefore are interesting for use as phosphorescent dopants in organic light-emitting diodes (OLEDs) and as luminescent probes in bioimaging. The majority of complexes investigated to date contain only one metal centre with multimetallic complexes becoming more widely studied in recent decades. This work explores the synthesis of novel dinuclear emitters based on cyclometallated Pt(II) and Ir(III) centres. In particular, complexes in which the metal centres are rigidly-linked via cyclometallating bridging ligands. The complexes described in this work are highly luminescent with high quantum yields in degassed solution and relatively short luminescence lifetimes. Dinuclear platinum(II) complexes linked via pyrimidine-based bis-bidentate ligands incorporating mono- and bis-thiophene cyclometallating units have been prepared and their photophysical properties investigated. These complexes were observed to emit in the orange (610 nm) and near-infrared (730 nm) regions of the spectrum for the mono- and bis-thiophene respectively, with relatively high quantum yields (φ = 0.15–0.85). A further dinuclear platinum(II) complex, rigidly-linked via a bis-tetradentate bridging ligand offering O^N^C^N coordination, was successfully prepared. To the best of our knowledge, this is the first example of di-platinum(II) complex in which the two metal centres are linked via this type of bridging ligand. Dinuclear iridium(III) complexes linked via bis-bidentate bridging ligands based on the central heterocycle pyrimidine have been prepared. These pyrimidine-linked complexes exhibited high quantum yields in degassed dichloromethane solution at room temperature, in the range 0.88-1.0. A representative structure is shown below. Variation of the monodentate chloride ligands to alternative ligands such as cyanide and acetonitrile was also investigated. Incorporation of a cyanide ligand was observed to blue-shift the emission relative to the analogous chloro complex. The effect of varying the central heterocycle of the bis-bidentate bridging ligand was investigated. The identity of the central heterocycle of the bridging ligand has been shown to have significant effects on the properties of the resulting dinuclear Ir(III) complexes, as is discussed below. Di-iridium(III) complexes linked via 2,5-pyrazine based bridging ligands have been successfully prepared. However, photodegradation of the complexes was observed in chlorinated solvents. To resolve this problem, a bis-bidentate bridging ligand incorporating a thiazolo[5,4]thiazole core was employed and the resulting di-iridium complex showed improved photostability. A 2,3-pyrazine-linked dinuclear iridium complex was synthesised and was observed to have a twisted geometry at room temperature and therefore, is chiral. Through a high-temperature NMR experiment, it was shown that this complex racemises at 80 °C. Finally, incorporating pyridazine as the central heterocycle leads to the sharing of a monodentate chloride ligand between the two iridium centres. This leads to the formation of a cationic dinuclear iridium(III) complex. This complex was investigated as a luminescent probe in bioimaging.
Supervisor: Kozhevnikov, Valery Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: F100 Chemistry