Pinar Kilickiran

Palladium-Catalyzed C—F Activation of Polyfluoronitrobenzene Derivatives in Suzuki—Miyaura Coupling Reactions

Highly fluorinated nitrobenzene derivatives are suitable substrates for palladium-catalyzed C-F bond arylation using readily available palladium catalysts under both conventional heating and microwave conditions. Arylation occurs ortho to the nitro group offering a synthetic route to polyfluorinated 2-arylnitrobenzene systems. The regiochemistry of the arylation reactions suggests that there is a significant directing interaction between the nitro group and the incoming nucleophilic palladium catalyst which is facilitated by the presence of several fluorine atoms attached the ring. Investigations into the regioselectivity and reactivity of several tetrafluoro- and trifluoronitrobenzene derivatives provides further evidence for the highly nucleophilic character of the oxidative addition step in contrast to the concerted mechanism of more conventional Suzuki-Miyaura coupling reactions involving aryl iodides and bromides.

Ultra fast polymer network blue phase liquid crystals

Polymer-stabilization of blue phase liquid crystal systems within a host polymer network are reported, which enables ultrafast switching flexible displays. Our newly developed method to stabilize the blue phase in an existing polymer network (e.g., that of a polymer network liquid crystal; PNLC) has shown wide temperature stability and fast response speeds. Systems where the blue phase is stabilized in an already existing polymer network are attractive candidates for ultrafast LCDs. The technology also promises to be applied to flexible PNLC and/or polymer dispersed liquid crystal (PDLC) displays using plastic substrate such as polyethylene terephthalate (PET).

Liquid crystal based sensors monitoring lipase activity: A new rapid and sensitive method for cytotoxicity assays

In this work we present liquid crystal (LC) based sensor devices to monitor cell viability. The sensing layer is composed by the LC and a planar monolayer of phospholipids. In the presence of minute traces of phospholipases, which hydrolyze enzymatically phospholipids, the LC-lipid interface is disintegrated. This event causes a change in orientation of the LC, which was followed in a polarized microscope. The lipase activity can be used to measure the cell viability, since members of this enzyme family are released by cells, as they undergo necrosis. The described sensor was used to monitor the presence of the lipases released from three different cell lines, which were either exposed to highly cytotoxic model compounds (sodium azide and paracetamol) or subjected to freeze-thaw cycles to induce cell death by a non-chemical based inducer for apoptosis, such as temperature. Finally, the comparison of lipase activity detected by a state-of-the-art fluorescence assay to the LC based system resulted in the superiority of the LC system concerning incubation time and sensitivity.

Highly fluorinated biphenyl ether systems as dopants for fast-response liquid crystal display applications

The overall display performance of representative commercially available +LC and –LC liquid crystal (LC) mixtures may be improved by the addition of small quantities of penta-, tetra- and tri-fluorinated biphenyl ether dopant systems. Synthetic routes for the preparation of the fluorinated dopants by nucleophilic aromatic substitution processes are described, and a range of electro-optical measurements of the doped LC mixtures, including LC rise and decay times, rotational viscosity, dielectric anisotropy, phase transition temperature and voltage holding ratios, were obtained. In general, the performance of the LC systems were improved by fluorobiphenyl ether doping, as determined by response time and rotational viscosity measurements, and figure of merit (FoM) calculations.

Investigation of reactive acrylic monomers for their effect on the temperature range and operating voltage of polymer-stabilised optically isotropic liquid crystal blue phases

Synthesis of various reactive acrylic monomers (RMs) to be used as components in liquid crystalline blue phase (LCBP) mixtures has been carried out in order to investigate their effect on temperature range and operating voltage. All the newly synthesised RMs were fully purified and characterised. These were added in various molar ratios to LCBP mixtures, which were stabilised by ultraviolet polymerisation, and improvements in the operating voltage and temperature range were studied. The compatibility of LCBP and monomer side-chains was investigated in terms of polarity and alkyl chain length.

Towards faster liquid crystals at lower driving voltages

Abstract— Response times and switching voltages of positive- and negative-type nematic liquid-crystal mixtures are improved by the addition of small amounts of diaryl-ether derivatives. The effect of such doping is directly seen as a reduction in the rotational viscosities of the mixtures. Despite their non-planar nature, the dopant molecules do not cause any detrimental changes to the black levels and the contrast ratios of the displays filled with the doped LC mixtures.

Nanoparticle‐embedded polymer‐dispersed liquid crystal for paper‐like displays

Abstract— A polymer-dispersed liquid-crystal (PDLC) matrix template embedded with nano/microparticles can be backfilled/infiltrated with a dye-doped liquid crystal for a paper-like reflective display. In this way, a desirable degree of diffusion can be realized to reduce the viewing-angle dependency of a gain reflector and metallic glare without changing other electro-optical properties.

17.4: Halogenated Non-Planar Dopants for Fast Response Liquid Crystals

We introduce a major step forward in achieving liquid crystal mixtures with desired performances such as fast response speeds, high VHR, low driving voltages and no detrimental perturbations in the liquid crystal alignments, thus undisturbed black level and contrast ratios, by the use of halogenated non-planar dopants.

Effect of long flexible chain reactive monomers on the operating voltage of optically isotropic blue phase liquid crystals

A reduction in operating voltage and switch-off time of polymer-stabilised blue phase (BP) liquid crystals has been achieved using reactive monomers (RMs) with long flexible alkyl side-chains. In place of a standard RM, two groups of novel RMs with and without alkyl side-chains have been synthesised. Polymer-stabilised BP systems were obtained by polymerising these RMs using UV irradiation, and their electro-optical properties were compared. Analysis of the results has provided molecular guidelines for future synthesis. The new RMs were purified and characterised chemically.

Liquid crystals as optical amplifiers for bacterial detection.

Interactions of bacteria with target molecules (e.g. antibiotics) or other microorganisms are of growing interest. The first barrier for targeting gram-negative bacteria is layer of a Lipopolysaccharides (LPS). Liquid crystal (LC) based sensors covered with LPS monolayers, as presented in this study, offer a simple model to study and make use of this type of interface for detection and screening. This work describes in detail the production and application of such sensors based on three different LPS that have been investigated regarding their potential to serve as sensing layer to detect bacteria. The LPS O127:B8 in combination with a LC based sensor was identified to be most useful as biomimetic sensing surface. This LPS/LC combination interacts with three different bacteria species, one gram-positive and two gram-negative species, allowing the detection of bacterial presence regardless from their viability. It could be shown that even very low bacterial cell numbers (minimum 500 cell ml(-1)) could be detected within minutes (maximum 15 min). The readout mechanism is the adsorption of bacterial entities on surface bond LPS molecules with the LC serving as an optical amplifier.