|Ph.D Student||Fridman Natalya|
|Subject||Chromotropism and Fluorescence Behavior of Imidazole|
|Department||Department of Chemistry||Supervisors||Professor Emeritus Menahem Kaftory|
|Professor Emeritus Shammai Speiser|
Recently, heterocyclic imidazole derivatives have attracted considerable attention because of their unique optical properties. The imidazole nucleus forms the main structure of some well-known components of human organisms, i.e. the amino acid histidine, viamin B12, a component of DNA base structure, purines, histamine and biotin. It is also present in structure of many natural or synthetic drug molecules.
We describe a comprehensive study of the spectroscopy, photophysics and photochemistry of wide range of class of lophine (2,4,5-triphenylimidazole) and its derivatives, some of them novel compounds, in order to establish their structure determining aspects of their optical properties.
We synthesized three different classes of lophine derivatives and their physicochemical properties were determined. Novel lophine derivatives: ortho-, meta- and para-substituted in the 2-phenyl ring and p-phenyl, p-tolyl, and p-anisyl rings in the 4- and 5-aryl rings are fluorescence compounds almost colorless or slightly yellow. Nitro-lophine derivatives are non-fluorescent compounds, which crystallize with guest molecules exhibiting various colors. The crystal structure of these compounds showed that solvent of crystallization and intermolecular hydrogen bonds play an essential role in the chromotropic behavior and in the packing of molecules in the crystals. Bisimidazole derivatives are fluorescence compounds. Some of them form crystal solvates, that show different colors and some of these compounds display piezochromism, photochromism and thermochromism in the solid state and exhibit solvatochromism, halochromism and photochromism in solution.
The X-ray crystal structures of lophine and bisimidazole derivatives with different solvents of crystallization, the spectroscopic properties, photochemistry of bisimidazole derivatives in solutions are reported. The thermal behavior of the crystalline compounds was studied by calorimetric method and it was shown that upon heating the crystal solvates lose the solvent molecules and the color is changed to the original color of the non-solvate parent compound. In all solvates the solvent molecules link host molecules through hydrogen bonds.
The photochemical properties of bisimidazole derivatives were studied by irradiating acetonitrile solutions with medium-pressure xenon lamp and their photochemical quantum yields, ranging from 0.0011 to 0.0024, together with the corresponding fluorescence quantum yields, ranging from 0.52 to 0.90 and life-times, ranging from 1.03 to 1.42 ns were determined. The photophysics of these lophine and bisimidazole derivatives was studied in details. The photochemistry of the two prototype derivatives was studied in solutions, showing an interesting general photochemical reaction between these derivatives and molecular oxygen.