Michael D. Wand

Electro-optic characteristics of de Vries tilted smectic liquid crystals: Analog behavior in the smectic A* and smectic C* phases

Chiral smectic A liquid crystal materials of the de Vries type (with molecules tilted relative to the layer normal) exhibit analog field-induced (electroclinic) optic axis rotation accompanied by an increase in birefringence. We identify two such de Vries smectic A* materials and use them to develop and test models for these characteristic electro-optic effects. These materials also exhibit colossal analog field-induced optic axis rotation in the lower temperature smectic C* phase, a consequence of polarization charge stabilization, and of polarization screening of the applied field in the liquid crystal.

The case of thresholdless antiferroelectricity: polarization-stabilized twisted SmC* liquid crystals give V-shaped electro-optic response

We have studied the three-component liquid crystal mixture reported to exhibit ‘thresholdless antiferroelectricity’ [Inui et al., J. Mater. Chem., 1996, 6, 671]. We find that the thresholdless or V-shaped switching is obtained in the absence of antiferroelectricity. This analog electro-optic response is due to the field-induced switching of a twisted smectic C* structure stabilized by polar surface interactions and by electrostatic bulk polarization charge interactions. The latter confine the director twist to thin surface regions leaving the bulk of the cell uniform, which gives good extinction at zero field. In sufficiently thin cells, such thresholdless switching can in fact be followed down to much lower temperatures, where the bulk would be antiferroelectric, but is maintained in the cells in the ferroelectric state by hysteresis from surface action.

Design and synthesis of ferroelectric liquid crystals. 15.1 FLC materials for nonlinear optics applications

Abstract We have recently reported the first FLCs designed specifically for large second order nonlinear optical (NLO) susceptibility χ(2); a series of o-nitro-1-methylheptyloxy biphenylbenzoates and phenyl biphenylcarboxylates. Properties of a stable room-temperature C* mixture of two such components (1:1 W316/W317 = MX5679) are presented. The nonlinear susceptibility, as evidenced by the Type 1 eeo deff for second harmonic generation (SHG) from 1,064 nm light for MX5679 is indeed large relative to other FLCs which have been evaluated for χ(2) (deff (ZLI3654) = 0.0016 pm/V, deff (SCE9) = 0.0037 pm/V, deff (MX5679) = 0.16 pm/V). The synthesis and some properties of second-generation FLCs designed for NLO applications is also described.

Large electroclinic effect in new liquid crystal materiala

Abstract We report a new liquid crystal material (W317) which has an unusually large electroclinic effect in a phase tentatively identified as smectic A. We show electroclinic tilt angles as large as 21°, and measurable tilt angles over a 40°C temperature range.

The effect of carborane, bicyclo[2.2.2]octane and benzene on mesogenic and dielectric properties of laterally fluorinated three-ring mesogens

Six series of structurally similar compounds containing 12- and 10-vertex p-carborane (A and B), bicyclo[2.2.2]octane (C), and benzene (D) were prepared and their mesogenic and dielectric properties investigated. Comparative analysis showed that all carborane derivatives form significantly less stable mesophases than their carbocyclic analogs, however they exhibit a relatively high shielding ability for lateral fluorination. Depression of the clearing temperature upon fluorination of series 1, 3, and 5 is approximately constant for each series A–D and correlates with the diameter of the ring (the slope = 14.8 °C A−1 and R2 = 0.997). Compounds in series 2 (X = F) were used as low concentration additives to a nematic host, 6-CHBT. Dielectric parameters were extrapolated to pure additives and analyzed using the Maier–Meier equation. The Kirkwood factors g and apparent order parameters Sapp that are required to reproduce the extrapolated dielectric values follow the trend in the size of ring . The smallest g (0.47) and the largest Sapp (6.3) are obtained for carborane 2A, and the largest g (0.69) and the smallest Sapp (0.7) are obtained for the terphenyl derivative 2D. The increase of Sapp in the series D→A corresponds to the increasing disorder of the nematic solution with increasing size of ring .

Stereocontrolled synthesis of substituted 2-alkoxytetrahydropyrans from meso-2,4-dimethylglutaric anhydride

Abstract Methods for efficient synthesis of A-ring fragments present in monensin and several of the nigericin group of ionophores and of α-multistriatin are described.

Evolution of the boulder model for the molecular origins of the polarization in ferroelectric liquid crystals

Abstract Development of a model relating the structure of FLC molecules to the sign and magnitude of the macroscopic ferroelectric polarization P exhibited by the supramolecular assembly in the C* phase is clearly an important and interesting goal. We have reported on our own simple stereochemical model for the molecular origins of P, which is based upon the concept that the sign and magnitude of P in FLCs can be understood in terms of a kind of molecular recognition occurring in the phase. Herein we present an overview of research aimed at testing this model by design, synthesis and characterization of FLC components with predictable properties.

Reversible photocyclization of achiral dithienylperfluorocyclopentene dopants in a ferroelectric liquid crystal: bistable SSFLC photoswitching

The spontaneous polarization (PS) of a ferroelectric liquid crystal is modulated reversibly by photocyclization (λ = 313 nm) of dithienyl- and dibenzothienylperfluorocyclopentene dopants with relatively high aspect ratios. Photocyclization of these dopants causes a decrease of PS due to a photomechanical effect which may originate from a loss of conformational flexibility of the dopant upon photocyclization. The degree of PS photomodulation increases with dopant concentration up to the solubility limit of 3 mol%. The maximum polarization photomodulation, ΔPS = 16.2 nC cm−2, is achieved at 6 K below the Curie point with the dopant 1,2-bis(5-(4-heptyloxyphenyl)-2-methylthien-3-yl)perfluorocyclopentene (3c, 3 mol%). The resulting PS photoswitch is fatigue resistant and photochemically bistable. Polarized spectroscopy experiments suggest that the dopants form homogeneous solutions with the FLC host and are integrated within the layer structure of the SmC* phase, with their molecular long axes approximately coincident with the director. To the best of our knowledge, this is the first example of a bistable ferroelectric liquid crystal photoswitch to be reported in the literature.

Ferroelectric properties of a series of core-fluorinated dopants containing the 2,3-difluoroalkoxy tail

Abstract Previous reports from these laboratories [1] have discussed the synthesis and properties of core-fluorinated phenylpyridines with an attached difluoroalkoxy tail. This paper discusses core-fluorinated phenylpyridine difluoroalkoxides and compares their properties to those of the corresponding phenylpyrimidines. The pyridine and pyrimidine series are found to be remarkably similar in properties. They have similar high polarizations and fast rise times, attractive in surfacestabilized ferroelectric liquid crystal (SSFLC) applications, and in high concentration have pitch properties compatible with deformable helix FLC applications.

Fast switching organosiloxane ferroelectric liquid crystals

We report the synthesis and characterization of organosiloxane 2-phenylpyrimidine mesogens with chiral (R,R)-2,3-difluorooctyloxy side-chains. These compounds form chiral SmA* and SmC* phases, and show remarkable electro-optical and alignment properties as surface-stabilized ferroelectric liquid crystals, including one of the fastest optical rise times (11 µs at T − TAC = −10 K and 6 V µm−1) for an organosiloxane mesogen.