The quantum yields for the interconversion of the cis and trans isomers of azobenzene and eight p-substituted derivatives have been measured at three wavelengths. The magnitude of the energy barrier separating the two isomers in excited states is considered, and it is
![ethyl 2-[4-oxo-5-(pyridin-3-ylmethylidene)-2-sulfanylidene-1,3-thiazolidin-3-yl]acetate Structure](https://image.chemsrc.com/caspic/229/6141-96-4.png)