|M.Sc Student||Diana Yanover|
|Subject||Chromotropism in Lophine Derivatives|
|Department||Department of Chemistry||Supervisor||Professor Emeritus Kaftory Menahem|
|Full Thesis text|
Many substances exhibit reversible variation of color under different physical or chemical conditions such as change of temperature, pressure, light irradiation, pH differences or solvent polarity. Such reversible color changes are collectively termed ‘chromotropism’.
The applications of chromotropic materials are very wide. Thermochromic materials have applications including temperature optical fiber sensors, writable/rewritable optical data storage and novel thermochromic and photochromic coloring agents. Applications of photochromic compounds are as optical power-limiting substances as in sunglasses or as photo-responsive materials.
Lophine, 2,4,5-Triphenyl-1H-imidazole, and its derivatives have a long history which begins with the discovery and investigation of the spectroscopic properties of these substances from the end of the nineteenth century until the 1960’s. Later it was discovered that lophine and its derivatives turned to chromotropic substances upon oxidation in solution. From the eighties there were reports that lophine derivatives show thermochromic behavior in the solid state and show chromotropic behavior upon crystallization with different solvents.
This research was focused on finding new thermo- and photochromic materials based on lophine and exploring the factors that are responsible for the crystal color change. We have synthesized lophine and a number of its derivatives: nitro-substituted as well as other derivatives. Some of these derivatives are entirely new compounds. Several of them were crystallized from different solvents. Their crystal structure and thermal behavior were thoroughly investigated and compared with other previously investigated lophines. Some of the crystalline compounds have shown that upon heating, crystal solvates lose solvent molecules and the crystal color is changed. Rationalization was given to the color aberrations based on molecular and crystal structure differences, calorimetric measurements and hot stage microscopy inspections.