A new type of multifunctional material based on dual photochromism of ternary chiral photochromic liquid crystalline copolymers for optical data recording and storage

An approach for the development of a new class of multifunctional photochromic liquid crystalline materials has been devised. Copolymerization of acrylic monomers allowed the preparation of ternary cholesteric copolymers containing nematogenic (phenyl benzoate), photochromic (azobenzene), and chiral photochromic side groups (benzylidene-p-menthanone). The phase behaviour and optical properties of such copolymers were studied. The synthesised copolymers are characterised by selective light reflection in the visible or IR spectral regions depending on the composition of the copolymers. The photochemical and photooptical properties of the synthesised copolymers were studied. The character of the photochemical processes in the above copolymers was shown to be controlled by wavelength lambda of incident light: as a result of light irradiation with lambda=366 nm, films or dilute solutions of copolymers experience E-Z photoisomerization of the azobenzene groups, whereas at lambda=313 nm, isomerization of both azobenzene and benzylidene-p-menthanone groups takes place. The action of UV light on the plane oriented films of copolymers leads to the E-Z isomerization of the chiral photochromic groups, and this isomerization is accompanied by untwisting of the cholesteric helix and by a shift of the selective light reflection wavelength to a long wavelength spectral region. On the other hand, irradiation of such films by polarised light with lambda=514 nm leads to the appearance of induced birefringence due to the existence of azobenzene groups which are capable of isomerization. The synthesised copolymers were shown to constitute a new class of multifunctional materials for data recording and storage.