Isomerization of <i>cis</i>-Azobenzene in the Solid Phase

Abstract

Abstract The thermal and photo-isomerizations of crystalline cis-azobenzene have been studied by infrared spectrophotometry in the temperature range of 36∼58°C, It has been found that the thermal isomerization follows Prout Tompkins’ law, and the values of k3 at 36, 50 and 58°C have been estimated. The Arrhenius plot of K3 is linear, and the activation energy of k3 is 31.3±0.3 kcal./mol. Pre-irradiation with a mercury lamp shortens the induction period, but it does not change the value of k3. On the other hand, the value of k3 is affected by the degree of grinding of azobenzene crystals. In this case, the activation energy is not altered by crystal grinding. The photo-isomerization at 12°C, in contrast to the case of thermal isomerization, has no induction period. However, the trans→cis photo-isomerization does not occur even if the crystal is treated by X-ray or by γ-ray preirradiation.