NOVEL PT(II) AND IR(III) COMPLEXES WITH NON-LINEAR OPTICAL AND LUMINESCENT PROPERTIES.

My PhD project has been focused on the synthesis of novel Pt(II) and Ir(III) complexes with nonlinear optical (NLO) and luminescent properties. Metal complexes with nonlinear optical properties: It is known that molecules formed by donor (D) and acceptor (A) groups linked with an unsaturated bridge having polarizable π-electrons are particularly NLO-efficient. Compared to organic compounds, metal complexes can offer further flexibility due to the presence of NLO-active charge transfer transitions between the metal and the ligands, usually at relatively low energy and of high intensity, tunable by virtue of the nature, oxidation state and coordination sphere of the metal center.[1] Based on the fact that metal alkynyl fragments are good donors in NLO-active systems, the idea of a hybrid with a C60-fullerene is highly intriguing because C60 is an electron deficient compound that can act as a good electron acceptor. For this reason, novel Pt-fullerene-alkynyl complexes were prepared and studied during the first part of my thesis. We applied the EFISH (Electric-field induced second harmonic generation) method to study their NLO response in solution. The huge values of µβEFISH observed for the fullerene platinum alkynyl derivatives are remarkable for neutral metal complexes. Indeed, to our knowledge, one of the complexes is characterized by the highest absolute value of µβEFISH reported for a platinum alkynyl complex. In order to evaluate also the solid state NLO properties (Second Harmonic Generation, SHG), composite films of some complexes dispersed both in polymethylmethacrylate (PMMA) and polystyrene were prepared. The preliminary data confirm the important role of the matrix whose specific functionalities can lead to host-guest interactions and affect the stability of the organized NLO molecules. During the thesis, various cyclometallated anionic Ir(III) complexes were also prepared in order to study their second-order NLO properties, by using the EFISH technique. To our knowledge EFISH studies on anionic metal complexes have never been performed. Preliminary results show that the prepared novel anionic iridium complexes are characterized by a good NLO response in CHCl3 solution. In parallel, some multifunctional cyclometallated neutral Ir(III) complexes were prepared, some of which resulted to provide good µβEFISH values. Metal complexes with luminescent properties: In the second part of my thesis, the luminescent properties of the prepared neutral Ir(III) complexes were investigated. Some of them turned out to be of interest for electroluminescent devices and biomedical application, showing a deep blue emission in degassed CH2Cl2. With such complexes OLED devices were fabricated. To our knowledge, they led to the bluest and best-performing iridium-based OLED reported so far (EQEmax = 13.4%).[2] Further, for some complexes the effect given by the addition of EWG elements on the ligand mojety was investigated. The most promising of complexes were used to fabricate an OLED devices. It turned out that one of above mentioned Ir(III) neutral complexes resulted to have also a remarkable cytotoxic activity. Besides, the internalization, cytotoxicity and photocytotoxicity were studied in collaboration with Dr. Simona Polo in the IFOM Institute in Milan. This complex appears to be a very promising photosensitizer for combined photodynamic therapy and cellular imaging. It has several desirable properties for the purpose: (i) it is highly phosphorescent and soluble; (ii) it easily enters into cells where it is concentrated in mitochondria, even at limited concentration; (iii) it is highly phototoxic upon irradiation with suitable light, but not cytotoxic in the dark.[3] In conclusion, during this thesis various novel Pt(II) and Ir(III) complexes were prepared and well characterized. Some of them show interesting second-order NLO properties whereas others are good candidates for the preparation of OLEDs. One of the complexes may offer interesting future potential for phototherapeutic applications in combination with emission imaging microscopy. References: [1] See for instance: Di Bella, S. et al. In Topics in Organometallic Chemistry 28. Molecular Organometallic Materials for Optics; Eds: Le Bozec, H. et al. Springer, 2010, 28, 1. [2] Pal A. K., Krotkus S., Fontani M., Mackenzie C. F. R., Cordes D. B., Slawin A. M., Samuel I. D. W., Zysman-Colman E. Accepted by Advanced Materials. [3] Colombo, A., Fontani, M. , Dragonetti, C., Roberto, D. , Williams, J.A.G., Scotto di Perrotolo, R., Casagrande, F., Barozzi, S., and Polo, S. submitted to Chem. Eur. J..