Tuning brightness and oxygen sensitivity of Ru(II) and Ir(III) luminophores

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The design of luminophores with high brightness is of crucial importance for many applications like the realization of Organic Light Emitting Diodes (OLEDs), and for biomedical imaging. However, despite the great number of works dedicated to the definition of the possible strategies for the realization of bright compounds, we are still far from a perfect luminophore for biological applications. The design of highly bright luminophores for biological imaging still constitutes a major challenge: the necessity of conjugating a high brightness (the product of the quantum yield and the molar extinction coefficient) with a low degree of oxygen quenching (which is necessary in order to keep a high luminescence in the oxygen-rich bio-environment) is still an open problem. Semiconductor Quantum Dots (QDs) are so far, the best candidates for biological applications since they show quantum yields closed to the unity and low oxygen sensitivity. However, despite the brilliant performances shown by QDs, their in vivo toxicity is still a major concern, especially from the perspective of a human application. Transition metal complexes are ideal candidates for the realization of bright luminophores, considering their high stability in biological environment and the possibility of tuning their optical properties by conveniently changing the structure of the ligands. Ruthenium(II) and iridium(III) complexes, in particular, are among the most studied transition metal complexes and the large amount of literature available makes them ideal candidates for further improvement. Two possible strategies can be followed in order to improve the optical properties of a luminophore: the decrease of its oxygen quenching degree and the amplification of its brightness. The first strategy is quite promising especially in order to improve the optical properties of Ir(III)-complexes, which show a pronounced oxygen sensitivity. Conversely, the brightness amplification via multiple labelling is particularly attractive for Ru(II)-complexes, which are barely sensitive to oxygen quenching but show also a low emission quantum yield. In this thesis both strategies have been applied in order to realise highly bright luminescent compounds based on Ru(II) or Ir(III) complexes. Moreover, since there is only a limited amount of literature concerning the tunability of the oxygen quenching of Ir(III)-complexes, a systematic study has been conducted in order to clarify the structure-quenching relationship.