Azobenzene-based photochromic change with irradiation

In reality, the liquid crystalline-to-isotropic phase transition temperature Tc) of the copolymer or LCP mixture with the cw-form Tec) is lower than that with the trans-isomer (Tct). The presence of the cw-azobenzene moieties depresses the transition temperature of the host liquid crystalline phase based on the concentration. If the temperature of the mixture T) is set between Tct and Tec and the sample is irradiated to cause trans-to-cis photoisomerization of azobenzene molecules, Tc decreases with an accumulation of the number of cw-isomer. When Tc becomes lower than the irradiation temperature, the liquid crystalline-to-isotropic phase transition is induced. The photoinduced phase transitions are interpreted in terms of a change in the phase transition temperature of PLCP systems on accumulation of one isomer of the photochromic molecule. As expected from Figure 7.5, AT (= Tct - Tec) is one of the most important parameters in the phase transition [1], When the temperature of systems is set below Tec, no phase transition is induced. When the temperature is set close to Tct, the amount of cw-azobenzene needed to lower Tc is relatively small, enabling one to effectively induce phase transition upon UV irradiation [10]. 

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