Vibrational excitation induced change of liquid crystalline domains in nematic and smectic phases

Effects of wavelength-selective infrared irradiations to nematic and smecti c phases on the domain structures were investigated using a free electron l aser (FEL) system for a rod-like mesogen possessing a lateral C=O group whi ch exhibits nematic, smectic A and smectic C phases. Them mesogen molecules tend to spontaneously align in a homeotropic way on BaF2 substrate. It was observed that the infrared irradiation of a pulsed laser whose wavelength corresponds to that of a C=O stretching absorption band (5.83 pm) induces t ransient turbulence of the liquid crystalline domains. This transient turbu lence was recovered to the original homeotropic alignment soon after the te rmination of irradiation. Some results strongly indicated that these phenom ena are induced by the thermodynamically non-equilibrium state generated by infrared laser pulse irradiation. These observations. imply that the domai ns as well as the collective modes of mesophase could be modified by infrar ed pulse irradiations with an appropriate power, whose wavelength correspon ds to the vibrational band of a specific chemical bond. (C) 2001 Elsevier S cience B.V. All rights reserved.