Optical switching in guest–host liquid crystal devices driven by photo- and thermal isomerisation of azobenzene

ABSTRACTWe investigated the phase transitions in guest–host liquid crystal devices induced by irradiation with unpolarised UV light. The photoinduced phase transition only occurred when the 4-pentyl-4-cyanobiphenyl host contained more than 4 wt% azobenzene guest molecules. The transmittance, optical switching time and relaxation time of the devices were estimated. The transmittance of the devices was controlled by changing the cell thickness. The optical switching and relaxation times of the devices were less than 120 and 300 s, respectively. The devices showed the unique switching property of forming the dark state when irradiated with unpolarised UV light. The dark state could be spontaneously changed to the transparent state by relaxation process when the UV light source was turned off.