Modification of the twist angle in chiral nematic polymer films by photoisomerization of the chiral dopant

A method for the production of polarization sensitive recordings in liquid crystalline polymers is presented. The system is based on local modification of the twist angle of chiral nematic polymer films. The twist angle of the polymer film is varied by modifying the chemical structure of the chiral dopant. Here a photoisomerizable menthone derivative is used that has a fivefold difference in helical twisting power between the E and the Z isomer. The twist angle of the film can be varied between -90 degrees and 0 degrees by introducing a nonphotosensitive chiral dopant with opposite twisting sense. Complex pictures with gray scales can be recorded in the films with black and white contrasts higher than 20. (C) 1999 American Institute of Physics. [S0021-8979(99)05011-2].