Linearly polarized light induces alternatively an optical axis perpendicula
r or parallel to the electric field vector of the incident light in films o
f photochromic polymers caused by the orientation of the 4-alkoxy-4'-cyanoa
zobenzene side groups. The orientational direction is exclusively governed
by the wavelength of the linearly polarized irradiation. Light, which estab
lishs a steady state between both azobenzene isomers, induces an orientatio
n perpendicular to (e) over right arrow caused by the conventional mechanis
m of photoorientation. Irradiating the same polymer film with red light an
orientational direction parallel to (e) over right arrow is generated by th
e photoselective formation of rod-like E isomers. The last orientation proc
ess occurs exclusively after a photochemical pretreatment with a shorter wa
velength generating Z isomers and destroying any initial order of the film.