A Versatile new family of highly luminescent platinum complexes: application from OLEDs to chemical sensors

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The research will explore applications of a new family of compounds containing platinum bound to NACANcoordinating ligands. By NAC^N, we mean an organic molecule that coordinates to the metal through two nitrogens and a central metal-carbon bond. The compounds are luminescent - they emit light when electrical or light energy is applied - and the short length of the Pt-C bond in our compounds makes the emission exceptionally bright. The objective of the research will be to put this bright emission to good use in two technologically important applications:(A). Organic light-emitting devices (OLEDs).Widely expected to be the next generation of display screen technology, OLEDs make use of small organic molecules or conjugated polymers, and offer advantages over existing LED technology; e.g. they can be formed as thin flexible plastics, so that TV screens could even be made by ink-jet printing. However, only a minority of the excited states that are formed when electrical charge is applied can emit light, namely the spin-paired singlet states. Luminescent heavy metal complexes are required to induce emission from the normally non-emissive triplet states (with electron spins parallel). We shall explore new NAC^N -coordinated platinum complexes for this purpose. They are likely to be very suitable for this application, because of their high efficiency of emission, charge-neutrality, ease of preparation, and amenability to derivatisation allowing a family of closely-related complexes with different colours of emission to be obtained. We will examine the effect of the fourth ligand on the stability and properties of the complexes, as well as working on other ligands offering NACAN coordination. A new strategy for tackling the problem of decreasing efficiency at high electrical currents will also be investigated, to allow brighter displays to be obtained.(B). A new ratiometric sensor for zinc ions.We will prepare a Pt(NAC^N) complex which incorporates a binding site for zinc ions on its back. The binding site to be considered will be a dipicolylanilino group, which is known to bind to Zn(II) with good selectivity over other metal ions under physiologically relevant conditions. We have discovered that the parent complexes can diffuse across cell membranes very rapidly and show no short-term cytotoxicity, making the Pt(NAC^N) unit attractive as the light-emitting component of a cellullar sensor. The new compounds will offer distinct advantages over currently available sensors for zinc, since they will allow time-resolved measurements to be made, offering greater sensitivity through discrimination from background fluorescence.