A chiral photochromic polyisocyanate was incorporated into a solid polymer matrix of poly(-methyl methacrylate) (PMMA), yielding an isotropic polymer film. Isomerization of the chiral photochromic azo side groups (cis-trans) triggers a reversible conformational change of the helical polyisocyanate backbone. Thus the chirooptical properties of the film can be switched photochemically. The isomerization of the helix is much slower than the isomerization of the azo side groups. Below T-g, the photochemically modified helix conformation is thus stable, despite thermal relaxation of the azo chromophores.