Synthesis and analysis of Nile Red functionalised Ru(II) and Ir(III) photosensitisers

Abstract

Nile Red (9-(diethylamino)-5H-benzo[a]phenoxazin-5-one) is a common organic dye that exhibits strong absorption of visible light, and is highly fluorescent. Despite these properties, examples of transition metal complexes that incorporate Nile Red into their molecular structures are rare, and their photophysical properties have not been extensively studied. Therefore, the aim of this thesis is to address the shortage of Nile Red-containing transition metal complexes currently in the literature. The attempted synthesis of an Ir(III) complex that utilises Nile Red as the cyclometalating ligand is reported. The structure of a side product formed during the failed cyclometalation reaction is fully elucidated and its photophysical properties analysed. A series of Nile Red derivatives are synthesised and the effects of structural modification on the optical properties of the derivatives are investigated. The Nile Red derivatives have been incorporated into Ru(II) polypyridyl and Ir(III) cyclometalated complexes, and their synthesis and structural characterisation are also detailed. Extensive photophysical analyses reveal that these complexes possess low-lying, non-emissive Nile Red-localised triplet excited states that are capable of generating singlet oxygen. Preliminary biological studies are reported that show these complexes can act as photosensitisers in photodynamic therapy. A series cyclometalated Ru(II) complexes have also been synthesised and characterised to add to the emerging field of developing photosensitisers capable of performing type-I photodynamic therapy.