The cis-trans Photoisomerization of Azobenzene

Abstract

The photoisomerization of cis- and trans-azobenzene in an n-hexane solution has been studied in the n-π* and π-π* absorption wave-length regions. The rate of isomerization has always been found to be proportional to the product of the incident light intensity and the concentration of cis- or trans-azobenzene. This simply means that the rate of isomerization is proportional to that of light absorption. Quantum yields of isomerization are independent of the temperature except for the trans→cis conversion caused by n-π* absorption, where the quantum yield is slightly dependent on temperature. The sum of quantum yields for cis→trans and trans→cis conversions caused by n-π* absorption is approximately unity, while the sum obtained with π-π* absorption is much smaller than unity. The mechanism of photoisomerization has been discussed with reference to these results.