Σχεδιασμός Και Σύνθεση Ετεροκυκλικών Και Συμπλόκων Ενώσεων Και Η Λειτουργία Τους Ως Μοριακών Διακοπτών Και Αισθητήρων

Abstract

Ιn this work, new heterocyclic products with structure based on 4,4'-bipyridine were designed and synthesized, and their ability to act as molecular switches and sensors was investigated.The first category of the synthesized compounds included complexes of iron(II) with Nmonosubstituted 4,4'-bipyridines (monoquats) acting as ligands. These products were proved to be solvatochromic. Significant shifts of the MLCT bands of these complexes, were observed under the alteration of the polarity of their environment. The impact of solvent polarity on the absorption spectra of the complexes was quantified using suitable empirical solvent polarity parameters. Through the resulting relationships the dominant solvent-solute interactions were revealed. The latter investigation was of great significance because it helped understanding their function as solvent polarity sensors with molecular dimensions. Furthermore the solvatochromism of these compounds was used in order to rationalize the molecular recognition effects taking place in the cybotactic region during the solvation of the solvatochromic solutes, in several binary solvent mixtures.Additionally some solvatochromic non symmetric viologens were synthesized. These products include an active methylene per molecule which is easily deprotonated even by relatively weak Lewis bases. A carbanion is formed even by simply dissolving the viologen in neat solvents, and that leads to the formation of a stable solvatochromic betaine readily affected by solvent polarity and solvent basicity. In the case of these compounds, the solvatochromic effects were quantified using suitable empirical parameters as well, including parameters describing solvent polarity and solvent basicity.Another family of new non symmetric viologens (N-methyl N'-aryl-viologens) were synthesized and their function as molecular sensors of ferrocyanide anions was studied. The pale yellow colored solutions of these compounds was observed to become deep blue in the presence of even small non stoichiometric quantities of ferrocyanide anions. The impact of the concentration of the mentioned anions on the PMR and UV-Vis-NIR spectra was also investigated. Additionally with the use of a suitable computer program, the LUMO energies of the electron withdrawing molecules (viologens) were calculated, and it was observed that they are perfectly correlated to the experimentally obtained maxima absorbance wavenumbers of the formed ionic pairs between the viologen cations and the ferrrocyanide anions. Thus the impact of the viologens' substituents on the stability of the excited states of the ionic pairs formed, was quantified.