Diazenes and the isomerization of azo compounds

In substituted diazenes, or azo compounds, the existence of two relatively stable cis and trani -isomers is of great experimental and theoretical interest. The photochemical conversion between these species has found many applications, including molecular switches, memory storage, and for conformational control in the regulation of biological processes.  

The presence of the two phenyl groups in azobenzene creates a relatively large preference for the trans-isomer (14.7kcal/mol calculated, 11.7-13.4kcal/mol experimentally ), primarily due to steric destabihzation of the c -azobenzene, which allows for thermal cw-tran -isomerization (with calculated and experimental barriers of 33 and 27kcal/mol, respectively). 

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