Chiral recognition on molecular nanowires from square planar platinum(II) complexes

This thesis presents the preparation and structural assignment of a novel chiral Pt(II) complex A by introducing an atropisomeric moiety at the periphery of monodentate isocyanide ligands. The overall charge-neutral complexes were completed by the bis-anionic tridentate trifluoromethyltriazolylpyridine (trzpy) ligand. A set of reference complexes comprised of new combinations of monodentate alkynyl- or isocyanide ligands with the known tridentate hexbzimpy and trzpy ligands was prepared. Absorption and emission spectroscopy of the resulting 1 and 4, showed the aggregate formation depending on concentration and solvent polarity. Furthermore, the novel atropisomeric Pt(II) complex, complex A, displayed the anticipated solvent-dependent aggregation towards chiral nanostructures. These nanostructures were investigated by scanning electron microscope imaging, NMR spectroscopy, circular dichroism, and UV vis absorption. Enantiospecific sensing of selected VOCs was investigated from the nanostructured system of complex A.
Indeed, interactions of enantiomeric small molecules with the crystal lattice provoked amplified changes in the absorption of complex A, exhibiting enantiospecific sensing behavior. In four different VOCs, namely R/S-2-BuOH, R/S-1-PhEtOH, R/S-α-pinene, and R/S-limonene the R and S enantiomers could be differentiated. Complex A aggregated to form a colloidal dispersion, which formed a new metal—metal-to-ligand charge transfer absorption band at 385 nm. Addition of enantiomers significantly affected the absorbance, which allowed for direct differentiation by UV-vis absorption measurements. The effect could also be measured by circular dichroism, further highlighting the stereospecific interactions between each enantiomer with aggregated complex A. UV-vis titrations of each selected VOC enantiomer revealed enantiospecific changes at sub-stoichiometric amounts. For the first time, reversible enantiospecific sensing has been realized from a molecular nanostructured material, especially from less functionalized enantiomer pairs (R/S-α-pinene, and R/S -limonene).