3. Introducing the azobenzene chromophore

Azobenzene is a molecule formed by a double bond between two nitrogen atoms $-\text{N}=\text{N}-$ connecting two phenyl rings. The term azobenzene or azo is used for the class of molecules whose basic structure is an azobenzene. The IUPAC (International Union of Pure and Applied Chemistry) name is diphenyldiazene. There are several properties common to almost all azobenzene molecules. The most obvious is the strong electronic absorption of the conjugated π system. The absorption spectrum can be shifted by molecular substitution groups from UV to visible wavelengths. The geometrically rigid structure and its aspect ratio along the molecule make it an ideal mesogenic system, i.e. one that can confer the properties of liquid crystals. The most interesting...