Photocontrol of Smectic Spacing

We report on the results of optical, X-ray and NMR studies of light-induced phenomena in smectic phases triggered by molecular phototransformations. UV irrddiation causes trans-to-cis isomerization of the dopant molecules while irradiation in thc visible part of the spectrum facilitates cis-to-trans lelaxation. Cis-to-trans isomerization decrcaws the smectic layers' spacing; as the result. a smectic slab undergoes an undulation instability andlor formation of focal conic domains. These textures arc nonuniform and scatter light; this effect can be used for optical data storagc. The opposite trans-to-cis isomelization disorders the orientation of molecules and increases the thickness of smectic layers. Two beams of different wavclengths with distinct yields of isomerisation can be used to write and crasc optical information.