Photoinduced nematic-isotropic phase transition: a case for the random-field Ising model

Experiments have been carried out on a photoactive guest-nonphotoactive host system exhibiting a photoinduced nematic-isotropic phase transition. It is shown that the phenomenon of photoinduced shift in the transition temperature is similar to the induction of cooperative chiral order in "sergeant-soldier" copolymer systems. An expression resembling the one given by the random-field model proposed for the latter system is seen to quantitatively describe the shift in the transition temperature as a function of the magnitude of the radiation.