LUMINESCENT AND NONLINEAR OPTICAL PROPERTIES OF ORGANOMETALLIC COMPLEXES

Organometallic chromophores with both luminescent and second-order nonlinear optical properties are of growing interest as new molecular multifunctional materials, since they offer additional flexibility compared to organic chromophores by introducing active electronic charge-transfer transitions between the metal and the ligand, which are tunable by virtue of the nature, oxidation state and coordination sphere of the metal centre. This is the main reason why our interest was brought in this specific research area. My PhD thesis is divided in two main parts: 1) Luminescent properties of cyclometallated metal complexes. 2) Second-order NLO properties of organometallic complexes and third-order NLO activity of organic π-conjugated and coordination compounds. The first section is dedicated to the preparation and study of the luminescence properties of some novel platinum(dipyridylbenzene) complexes. These organometallic compounds, known for being extremely bright emissive and having long lifetimes, are of particular interest for applications in electroluminescent devices. My aim was to achieve mono- and dinuclear complexes possessing emission properties that can be tuned with external factors. The two dinuclear platinum(II) complexes that I synthesized alternate monomer-like and eximeric emission, depending on the temperature, the solvent and the presence of metal cations in solution. The mononuclear platinum(II) complexes that I studied, instead, bear a photochromic unit linked with different tethers to the metal moiety: this allows the modulation of their switching ability and the study of the effect of the linker. These complexes were prepared in Rennes, France, during my stay in the group of Dr. V. Guerchais. The second section is dedicated to the second-order nonlinear optical properties of mononuclear platinum(dipyridylbenzene) complexes. In the first place, we will discuss how the second-order NLO properties of such compounds can be modified by virtue of the presence of different π-conjugated pendants linked to the central metal unit with different bridges: this will allow a fine tuning of the NLO properties. Secondly, we will study related photochromic platinum(II) complexes and see that their second-order NLO properties are switchable, too. The two-photon absorption (TPA) ability of different organic π-conjugated and organometallic complexes will be discussed. At first, the outstanding TPA properties of some 3,4,9,10-perylenetetracarboxylic diimide derivatives will be presented. These purely organic compounds will be used as springboard to achieve new multinuclear ruthenium(II) complexes with a highly π-conjugated ligand. Afterwards, the TPA activity of some ruthenium(II) σ-acetylide and iridium(III) tris-(phenylpyridine) complexes will be discussed. The two-photon absorption measurements were performed in the laboratory of Dr. K. Kamada, in Ikeda, Japan, during my stay there. Throughout this dissertation, the luminescent, second- and third-order nonlinear optical properties of a new multifunctional cationic iridium(III) complex will also be presented.