ROLE OF GUEST-HOST INTERMOLECULAR FORCES IN PHOTOINDUCED REORIENTATION DYED LIQUID-CRYSTALS

An experimental study of the photoinduced molecular reorientation of d yed liquid crystals for a set of guest-host combinations is reported. We find large variations in the magnitude of the effect for different dyes but also for different hosts, with polar hosts resulting often si gnificantly more effective than nonpolar ones. The data are interprete d in terms of a kinetic mean-field model for the dye molecule rotation al dynamics and interaction with the liquid crystal host. The results point to a significant variation of guest-host intermolecular forces u pon photoinduced electronic excitation of dye molecules. This force va riation is reflected in a variation of dye molecule physical parameter s such as the rotational friction coefficient and the orientational me an-field energy. (C) 1997 American Institute of Physics. [S0021-9606(9 7)51647-3] .