PHOTOISOMERISING EFFECTS IN NITROAZO FLEXOELECTRIC DIMERIC NEMATIC SYSTEMS

Abstract

The photoisomerisation of a flexoelectric chiral nematic bimesogen system dyed with an azo dye has been investigated. The host material has a pitch and field dependent tilt angle that are temperature independent. Upon illumination by ultra violet, the azo dye molecules undergo a shape change from their trans to cis isomer. The effect of the shape change of the dye on the mixture is to decrease the I-N* transition temperatures, to increase the response times and to decrease the transmitted optical intensity. For the same reduced temperatures, the tilt angles, pitch and threshold voltages for the transition from focal conic to homeotropic textures are unchanged. The macroscopic parameters observed suggest that the orientational order parameter of the system is reduced by UV illumination. The cis isomers do not appear to separate from the host material or significantly change the flexoelectric coefficient.     

EFFECT OF AZIMUTHAL SURFACE LAYER ANCHORING ON FIELD-INDUCED LAYER REORIENTATION IN A SHORT PITCH FERROELECTRIC LIQUID CRYSTAL

Abstract

The concept of the azimuthal surface layer anchoring (ASLA) is introduced to describe the field-induced layer reorientation in a short pitch ferroelectric liquid crystal (FLC). It was found that for the larger ASLA, the smaller layer reorientation occurs and saturates in the high field regime, especially near both surfaces. The ASLA tends to renormalize the surface interactions which produce the asymmetric director switching. It is suggested that the ASLA acts as a hindered restoring force for the layer reorientation.     

OPTICAL TRANSMISSION AND POLARIZATION SWITCHING PROPERTIES OF A FERROELECTRIC LIQUID CRYSTAL CELL WITH A STABLE TWISTED STATE

Abstract

Ferroelectric liquid crystal cells with a stable twisted state were prepared. Dynamic processes of molecular reorientation in a stable twisted state under an applied electric field have been investigated by observing the optical transmittance and polarization switching current with simultaneous observation of the texture change.     

ELECTROOPTIC EFFECTS OF THICK FREELY SUSPENDED FERROELECTRIC LIQUID CRYSTAL FILM AND CELL

Abstract

Electrooptic effects of thick freely suspended ferroelectric liquid crystal films and conventional cells that are thicker than helical pitch have been studied. A very slow molecular motion was observed in the case of the thick films that have no solid surface.     

An interesting inclusion phenomenon of 2,2′-bis(diphenylhydroxymethyl)binaphthyl with some organic solvents and crystal structure of the host:guest complex with ethyl acetate

Recrystallization of 2,2-bis(diphenylhydroxymethyl)binaphthyl in ethyl acetate, dichloromethane/cyclohexane, dichloromethane/hexane, and chloroform/hexane gave solvent inclusion compounds as colorless prisms which were confirmed by thermal analysis,¹H NMR (CDCl₃) spectral data, and elemental analyses. The crystal structure of 2,2-bis(diphenylhydroxymethyl)-binaphthyl: ethyl acetate was elucidated by X-ray crystallography.     

Synthesis and supramolecular interactions involved in the crystal structure of (2,4,10,12-tetrabromo-6,7,14,15-tetrahydro-6, 14-thiacycloocta[1,2-b:5,6-b’]diquinoline)2·(1,1,2,2-tetrachloroethane) inclusion compound

The tetrahalo aryl inclusion host 2,4,10,12-tetrabromo-6,7,14,15-tetrahydro-6,14-thiacycloocta[1,2-b:5,6-b’]diquinoline 3 was re-synthesized to explore its ability to trap toxic polychlorinated hydrocarbons such as 1,1,2,2-tetrachloroethane (TCE) in the form of host–guest compound. Host 3 crystallizes from a fresh sample of TCE to form an inclusion compound of the formula (3)₂·(TCE) in triclinic system, space group P-1, with a = 7.7732(16) Å, b = 10.739(2) Å, c = 14.816(3) Å, α = 97.329(4)°, β = 98.619(4)°, γ = 103.359(4)°, V = 1172.7(4) ų, and Z = 2. The X-ray crystal structure of the (3)₂·(1,1,2,2-TCE) is described and analyzed in terms of crystal engineering and supramolecular chemistry. The hosts assemble by means of different types of packing motifs. The included TCE molecules are enclosed within host molecular pens. Novel halogen···halogen intermolecular interactions as well as other non-covalent intermolecular interactions involved in the crystal structure are presented and proved to play an important role in linking these host–host, host–guest, and guest–guest building blocks.