Cyclometallated platinum compounds: optical and biological applications

Abstract

[eng] This Doctoral Thesis is focused on the synthesis of cyclometallated platinum compounds with different structural modifications rationally designed specifically for biological or optical applications. Specifically, tridentate [C,N,N’] and [N,C,N] cyclometallated compounds have been synthesised, differing in their oxidation state, the nature of the cyclometallated ligand, with variations in the rigidity and aromaticity, and with a variety of ancillary ligands. Several synthetic methodologies have been employed and the correct formation of the compounds has been checked by a great variety of techniques such as NMR and infrared spectroscopy, mass spectrometry elemental analysis and single crystal X-ray diffraction. Concerning biological applications, several compounds with anticancer properties have been successfully synthesised, obtaining some species with a high efficacy and minimal toxicity studied through cell viability assays. Additionally, several of the designed compounds presented a complete absence of cross-resistance and thanks to additional testing such as cyclic voltammetry, DNA interaction studies and cell-cycle phase distribution experiments, it has been observed that they present mechanisms of action not analogous to those of the clinically approved drugs. Concerning optical applications, the tuning of the structure of the compounds, especially in the cyclometallating ligands, has been key to achieve efficient phosphorescent platinum(II) compounds with various emissive states. Both emission quantum yields and lifetimes have been determined and DFT calculations have allowed a further understanding of the molecules excited states. Additionally, modification of the ancillary ligands, the solvent, the concentration or the presence of an additional metallic cation have been used as a strategy to promote a red-shift in the emission through the formation of aggregates or heterometallic compounds. Finally, one compound has been selected and tested for the preparation of a Light-Emitting Electrochemical Cell (LEEC) obtaining novel results for a platinum-doped device which are competitive with those reported in the literature for other metals and, to the best of our knowledge, the most efficient platinum system used for LEEC applications.