Determination of absolute configuration of chiral tripodal metal complexes by the exciton coupling method

This thesis describes the development of a non-empirical method for the determination of the absolute configuration of chiral amino acids and alcohols. This approach utilizes exciton coupled circular dichroism (ECCD) to determine optical activity.{09}ECCD determines the handedness of the effective transition moments of two or more chromophores that are in close proximity and fixed in space. This dissertation describes the synthesis, characterization, and circular dichroism spectra of quinoline and porphyrin derivatized chiral tripodal metal complexes. By using tetraphenylporphyrins, the spectroscopic sensitivity is increased and the absorption is shifted from the UV to the visible region. The oxidation state of the metal appears to affect the ligand geometry and thus has an effect on the chiroptical response.; Chapter 1 gives a broad introduction to the world of chirality and how this theme connects to everyday life, in particular to beauty and art.; Chapter 2 describes structural studies of a chiroptical absolute configuration assignment method for amino acids that are easily derivatized with quinoline chromophores.{09}Complexation of these ligands with Cu(II) enforces a defined geometry between chromophores. The sign of the measured ECCD spectra was in agreement with the configuration at the chiral center. Furthermore, this chapter demonstrates that the differential extinction coefficient (Δϵ) is linearly related to the enantiomeric excess.; Chapter 3 reports the evolution of the above method by successful syntheses of bis-tetraphenylporphyrin derivatized L-methioninol and L-methionine. The bisignate CD signature shifts from the UV region of the quinolines to the visible region of the porphyrins. This improves the chiroptical properties of the system since many solvents absorb in the UV. Therefore, this new system allows for a wider selection of solvents and the use of visible light as opposed to higher energy UV light.; Chapter 4 discusses studies of a molecular redox switch, which is based on quinoline and porphyrin-derivatized L-methioninol. The quinoline system allows for complete inversion of the chiroptical response upon reduction of Cu(II) to Cu(I), classifying this as a (+)/(−) switch. The porphyrin system demonstrates on/off properties depending on the redox state of the metal.; Chapter 5 explores the possibility of chiroptical materials containing phthalocyanine chromophores.