Cholesteric mixture containing chiral-photochromic and diarylethene dopants as novel material with dual photochromism

New cholesteric polymeric mixture containing nematic side-chain homopolymer, 2 wt% of photochromic diarylethene dopant and 5 wt% of chiral-photochromic dopant based on cinnamic acid and isosorbide was prepared. Upon UV irradiation of planarly-oriented mixture films at room temperature, a transformation of open colorless form of diarylethene dopant into a closed colored form takes place, which is followed by the appearance of an intense absorption maximum in the visible spectral region and decreasing selective light reflection intensity, This process is photo- and thermo-reversible and many cycles 'recording-erasing' can be realized. UV irradiation and subsequent annealing of the films lead to untwisting of the cholesteric helix and cause an irreversible shift of selective light reflection to the long-wavelength region. This process is explained by the E-Z isomerization of chiral photochromic groups of the dopant relative to a C=C bond accompanied by a decrease in their hoisting ability, It has been shown, that the use of the material prepared in this work provides an opportunity to record two images at the same time: one image is due to a change in the helical pitch and another (second) image is due to the photochromism of diarylethene dopant. It is pertinent to note that using the approach developed in this work allows one to widely vary the range of materials exhibiting dual photochromism. It was demonstrated that the mixture under study shows advantage as new photosensitive material for optics, optoelectronics and data recording. Copyright (C) 2002 John Wiley Sons, Ltd.