Mixtures of a photosensitive chiral dopant based on (—)-menthone with left-handed and righthanded cholesteric copolymers were prepared. The phase behaviour and optical properties of the mixtures prepared were studied. The action of UV radiation on planar oriented films of such systems was shown to induce dramatic changes in the maximum reflection wavelength as a result of E-Z isomerization of the dopant molecules. The kinetics of photoisomerization of such mixtures in solution and in the bulk were investigated at different temperatures. The above mixtures can be considered as promising and uprecedented materials for coloured data recording and storage.