Essay on Experiment on Photocromism and Piezochromism
1363 WordsSep 25, 20146 Pages
Experiment B10- Photocromism and Piezochromism
Reece Harms 4320288
This experiment investigates an oxidative coupling reaction in an to synthesise triphenylimidazole dimer from 2,4,5-triphenyl-1H-imidazole. The resulting compound was investigated for both photochromic and piezochromic properties by way of formation of a stable radical, utilizing visual observations and UV-Vis as a means of distinction. Both the oxidative coupling reaction and the dimers interaction with light are depicted in the reactions in figure 1.
Figure 1: Oxidative Coupling reaction of 2,4,5-triphenyl-1H-imidazol
Ethanol (100ml), potassium hydroxide (8.065g, 2.568mmol) and water (5ml) were added in order to…show more content…
This could be improved by utilizing an inert atmosphere of solely nitrogen. Melting the compound resulted in an intensely dark purple liquid. This is a result of the resonance stabilized radical being formed by the homolysis of the carbon-to-carbon bond validating the photochromic properties. The colour change further substantiates that the desired product was produced despite the inaccuracies in melting point values. Homolytic cleavage of the dimer prepared by solvation with toluene results in a deep purple solution confirming the formation of the resonance stabilized radical.
After placing in darkness the colorless solution resulted by reformation of the radical intermediates to a new thermodynamic product via C-N bond at room temperature. UV-Vis was conducted on the solution before and after the irradiation with sunlight: UVtoluene 554.92nm, A=0.12 before irradiation and A=1.05 after. The peak at 554.92nm corresponds to yellow/green light and its complementary colour is red/violet. This validates the solutions violet color. The increased absorbance was accounted for an increase in the radical component. The radical was formed when exposed to light, which was visually apparent with the purple coloration and proved the thermodynamic dimer was also photochromic. When dimer 4 is exposed to light photons collide with the molecule and impart energy upon them. This energy is significant enough to break the bond between the two rings and results