LOW-TEMPERATURE LASER FLASH-PHOTOLYSIS AND SPECTRAL STUDIES OF METHYLRED

The low temperature flash photolysis and spectral studies of Methyl Re d {2-[4-(dimethylamino)phenylazo]benzoic acid) show the presence of fo ur conformers in equilibrium. Besides the common cis and trans conform ers, there are two types of quinoid zwitterions. The absorption intens ity at room temperature is mostly contributed by quinoid zwitterions. In methyl cyclohexane the absorption maximum of the trans conformer is at 420 nm and those of two zwitterions are at 475 and 455 nm, respect ively. From flash excitation spectra, the cis conformer appears to sho w an absorption maximum at 350 nm. The distribution of the species cha nges on flash excitation and the normal distribution is restored via o ne or more equilibrium steps as indicated by the negative activation o f the process.