CIS-TRANS PHOTOISOMERIZATION OF 4-NITROSTILBENES

Results on cis-trans photoisomerization of 4-nitrostilbenes obtained in recent years are summarized and discussed. Mechanisms for the direct trans →cis and cis -> trans photoisomerization are presented. The trans cis → isomerization occurs via a triplet state as intermediate whereas in the cis → trans isomerization the main route bypasses the triplet state. The triplet state shows a confi- gurational equilibrium between the planar trans (tr) and more twisted forms (p 3or c). The equilibrium is mainly on the trans side. The influence of substitution, temperature, viscosity, solvent, and addition of quenchers on quantum yields of isomerization, fluorescence studies, and spectroscopic as well as kinetic laser flash photolysis results support the above conclusions. © IUPAC