Helical chirality of azobenzenes induced by an intramolecular chiral axis and potential as chiroptical switches

The cis and trans forms of the azobenzene skeleton differ significantly in length and therefore are frequently used as photochromic parts for changing absorption and fluorescence properties, in addition to association constants when they are hosts.Although optically active compounds with azobenzene adducts have been reported,few studies have examined the asymmetry of the azobenzene moiety itself. Haberhauer and Kallweit have investigated the twisting direction of the cis-azobenzene moiety by studying the helical chirality linked to a chiral cyclic imidazole tetrapeptide, possessing four asymmetric centers.The axially chiral binaphthyl is rigid in the rod direction, but around the axis has a wide and flexible asymmetric field. Thus, binaphthyl skeletons have been employed in asymmetric organocatalysis,molecular recognition,and chiral doping of liquid crystals.