Photochromic Reactions of Two Azobenzene Chromophores in a Chiral Cyclohexane Moiety

A chiral cyclohexane containing two photochromic azobenzene units, (1R,2R)-N,N′-bis[4-(phenylazo)benzylidene]-1,2-cyclohexanediamine, was synthesized in an attempt to construct a molecule which shows a large optical rotation change due to photoirradiation. The CD spectrum dramatically changed depending on the configuration of the two azobenzene units. The specific rotations of (E,E)-, (E,Z)- and (Z,Z)-isomers were −1400°, −940°, and −670°, respectivly, while that of the monosubstituted chiral cyclohexane, (1R, 2R)-N-[(4-phenylazo)benzylidene]-N′-benzylidene-1,2-cyclohexanediamine ((E)-isomer), was only −470°. There was no difference in the photoisomerization rates of the azobenzene chromophores attached to chiral and nonchiral cyclohexanes.