With many azobenzene derivatives commercially available, properties of the OCCphotoswitch system can be tuned using varying functionalizations. Several synthetic routes can access those derivatives that are not commercially available. A widely used synthetic route involves diazotizing an aromatic amine using sodium nitrite in the presence of strong acid to afford the resulting diazonium salt, which can then be coupled with phenol to give azobenzene product (Figure ). Alternatively, the Mills reaction can also be used where an aromatic amine is oxidized to a nitroso intermediate (Figure ). This species can then be reacted with a separate aromatic amine to yield the azobenzene. For symmetric azobenzenes (bi-OCCs), the desired product can be afforded through reductive coupling of aromatic nitro compounds using a reducing agent or oxidative coupling of aromatic amines using an oxidizing agent to achieve the same transformation (Figure ) 141,142 .