PHOTOCHEMICAL MODIFICATION OF THE DYNAMIC BEHAVIOR OF LIQUID-CRYSTALS

The E/Z photoisomerization of azobenzene modifies order and molecular dynamics of liquid crystalline guest host systems. In nematic systems the degree of order is decreased and an increase of the real part of d ielectric function was found upon UV irradiation. In the case of the s mectic B mesophase of CCH-2 a phase separation is observed for the gue st-host system forming coexisting smectic s(B) and nematic domains. Re laxation processes which are characteristic for both phases are observ ed simultaneously. The irradiation procedure increases the extent of t he phase separation, whereas the s(B) domains become more ordered comp ared to the non-irradiated case and the nematic domains become enriche d with the azobenzene molecules. The relaxation strength of the relaxa tion process in the s(B) phase decreases whereas its rate is shifted t o higher frequencies.