Electroclinic behaviour of polymer doped low molar mass ferroelectric liquid crystals

Abstract

Recently there has been much interest in the electroclinic effect due to its potential application in high speed optical modulators and grey scale displays. In present materials, however, the electroclinic effect is very dependent on temperature and falls off rapidly with increasing temperature. This limits the useful device operating range. In this paper the electroclinic behaviour of new, side chain polymer doped, low molar mass ferroelectic liquid crystal mixtures is reported. By measuring the rate of change of the electroclinic coefficient with temperature it is shown that the temperature range over which the electroclinic effect exists increases with polymer concentration. Data are also presented on electroclinic response times.     

Electrically-induced optical storage effects in smectic polysiloxanes A variable transmission device

Abstract

Changes in the optical transmission induced by electric fields have been studied in a smectic side-chain polysiloxane liquid crystal. The transmission varied from effectively zero, for a highly scattering (opaque) texture, to total, for a homeotropic texture, on increasing the applied voltage across the material. The field-induced textures were durably stored in the smectic phase, enabling the order parameter of the side groups to be studied by dielectric relaxation measurements. For the highly transparent texture, a side group order parameter of 0-92 has been observed.     

Crown Ether Appended Amidopyrrole Clefts

Two new pyrrole amide–crown ether conjugates have been synthesised and their anion complexation properties studied in the absence and presence of stoichiometric quantities of sodium or caesium cations. Certain anions are sequestered by the metal cation in DMSO-d ⁶ (0.5% water), however, in one case a 4.7 fold increase in the fluoride affinity of the receptor was observed upon addition of caesium cations.     

Crystallographic and Solution Anion Binding Studies of Bis-amidofurans and Thiophenes

A variety of furan and thiophene amide and thioamide cleft type anion receptors have been synthesised and crystallographically characterised. Unlike 2,5-diamidopyrrole anions, analogous 2,5-diamidofurans and thiophenes do not interlock in the solid state. The anion binding properties of these receptors have been investigated in DMSO/0.5% water solution using ¹H NMR titration techniques. Solution studies and solid-state evidence suggests that the thiophene receptors may utilise a thiophene CH hydrogen atom for hydrogen bond formation to anions with a 2,4-diamidothiophene showing similar anion binding affinities to a 2,5-diamidopyrrole.     

A Structural and Theoretical Study of the Thiophosphinite and Dithiophosphinate Anions

Two novel lithium compounds containing either the phosphorus-chalcogenide anions [Ph ₂ PS]^? or [Cy ₂ PS ₂ ]^? were isolated as decomposition products in the attempted formation of phospha(V)guanidinate anions. Lithium diphenylthiophosphinite was structurally characterized as the dimeric TMEDA adduct [Li(Ph ₂ PS)(TMEDA)] ₂ (1), in which a rare example of the κ ¹ -S bonding mode was observed for the anion. The dicyclohexyldithiophosphinate anion was incorporated into an aggregated structure with molecular formula [Li ₅ (Cy ₂ PS ₂ ) ₄ (OH)] ₂ (2). DFT calculations were performed on the isolated [R ₂ PS]^? and [R ₂ PS ₂ ]^? anions (R = Ph, Cy), indicating delocalization of electron density into the P-S bonds for each model, in agreement with bond-lengths taken from crystallographic data.     

Reactivity of Fluoro‐Substituted Bis(thiocarbonyl) Donors with Diiodine: An XRD,FT–Raman,and DFT Investigation

The reactions of 1,3,8,10‐tetrakis(4′‐fluorophenyl)‐4,5,6,7‐tetrathiocino[1,2‐b:3,4‐b′]diimidazolyl‐2,9‐dithione ( 4 ) and molecular diiodine afforded spoke adducts with stoichiometries 4·I2 and 4? 3I₂, isolated in the compound 4? 3I₂ ? xCH₂Cl₂ ? (1?x)I₂ (x=0.70), and characterized by single‐crystal XRD and FT–Raman spectroscopy. The nature of the reaction products was investigated under the prism of theoretical calculations carried out at the DFT level. The structural data, FT–Raman spectroscopy, and quantum mechanical calculations agree in indicating that the introduction of fluorophenyl substituents results in a lowering of the Lewis basicity of this class of bis(thiocarbonyl) donors compared with alkyl‐substituted tetrathiocino donors and fluorine allows for extended interactions that are responsible for solid‐state crystal packing.     

Oxidopolyborate chemistry: The self-assembled,templated, synthesis,and an XRD study of a 1-D coordination polymer, [Cu(en){B6O7(OH)6}].3H2O (en = 1,2-diaminoethane)

Abstract

[Cu(en){B₆O₇(OH)₆}]^.3H₂O (1) (en = 1,2-diaminoethane), obtained as a crystalline solid in low yield (31%) after prolonged standing of an aqueous solution initially containing [Cu(en)₂](OH)₂ and B(OH)₃ (1:7 ratio), was characterized by thermal analysis (TGA/DSC), ¹¹B NMR and IR spectroscopy, powder XRD, and single-crystal XRD studies, and magnetic susceptibility measurements. The single-crystal X-ray diffraction revealed that the oxidoborate complex is a 1D coordination polymer with the hexaborate(2-) ligand bridging two hexacoordinate Cu^(II) centers, in an alternating a fac-tridentate (κ³-O) and monodentate (κ¹-O) arrangement. Cu-O coordination bonds and extensive H-bonding networks promote and stabilize the self-assembly of [Cu(en){B₆O₇(OH)₆}]^.3H₂O from the Dynamic Combinatorial Libraries of available reactants. [Cu(en){B₆O₇(OH)₆}]^.3H₂O is thermally decomposed to CuB₆O₁₀ in air at 700?°C.     

A Photophysical Study of Sensitization‐Initiated Electron Transfer: Insights into the Mechanism of Photoredox Activity

The development of photocatalytic reactions has provided many novel opportunities to expand the scope of synthetic organic chemistry. In parallel with progress towards uncovering new reactivity, there is consensus that efforts focused on providing detailed mechanistic insight in order to uncover underlying excited‐state reactions are essential to maximise formation of desired products. With this in mind, we have investigated the recently reported sensitization‐initiated electron transfer (SenI‐ET) reaction for the C?H arylation of activated aryl halides. Using a variety of techniques, and in particular nanosecond transient absorption spectroscopy, we are able to distinguish several characteristic signals from the excited‐state species involved in the reaction, and subsequent kinetic analysis under various conditions has facilitated a detailed insight into the likely reaction mechanism.     

Possible transition from rod-like to disc-like behaviour in ortho-metallated imine complexes of palladium(II): crystal and molecular structure of three palladium complexes

Two series of ortho-metallated palladium imine complexes are reported that contain a coordinated β-diketonate group. In one group the chain length of the imine is varied while the β-diketone is unchanged; in the other the imine chains are both fixed as methoxy and the structure of the β-diketonate is varied. The mesomorphism of these new complexes is reported and discussed in relation to the search for materials showing a biaxial nematic phase.     

2,4‐Di­hydroxy‐1,3‐bis­(methoxy­carbonyl­methoxy)­calix­[4]­arene and 1,3‐bis­(ethoxy­carbonyl­methoxy)‐2,4‐di­hydroxy­calix­[4]­arene chloro­form solvate

The two title calix­[4]­arene compounds, C₃₄H₃₂O₈, (I), and C₃₆H₃₆O₈·CH₃Cl, (II), respectively, which differ only in the size of the alkyl function on the pendant ester group, are compared. Compound (I) forms a novel supramolecular array, whilst (II) fails to do so due to accommodating a chloro­form guest molecule in the lower‐rim cavity.