Daniel J. Dyer

Computational studies on response and binding selectivity of fluorescence sensors.

Using a computational strategy based on density functional theory calculations, we successfully designed a fluorescent sensor for detecting Zn(2+) [J. Phys. Chem. B 2006, 110, 22991-22994]. In this work, we report our further studies on the computational design protocol for developing Photoinduced Electron Transfer (PET) fluorescence sensors. This protocol was applied to design a PET fluorescence sensor for Zn(2+) ions, which consists of anthracene as the fluorophore connected to pyridine as the receptor through dimethylethanamine as the linker. B3LYP and time-dependent B3LYP calculations were performed with the basis set 6-31G(d,p), 6-31+G(d,p), 6-311G(d,p), and 6-311+G(d,p). The calculated HOMO and LUMO energies of the fluorophore and receptor using all four basis sets show that the relative energy levels remain unchanged. This indicates that any of these basis sets can be used in calculating the relative molecular orbital (MO) energy levels. Furthermore, the relative MO energies of the independent fluorophore and receptor are not altered when they are linked together, which suggests that one can calculate the MO energies of these components separately and use them as the MO energies of the free sensor. These are promising outcomes for the computational design of sensors, though more case studies are needed to further confirm these conclusions. The binding selectivity studies indicate that the predicted sensor can be used for Zn(2+) even in the presence of the divalent cation, Ca(2+).

Giant surface electroclinic effect in a chiral smectic A liquid crystal

We report the observation of a very large surface electroclinic effect in the smectic A* phase of a chiral liquid crystal. In planar-aligned cells of enantiomerically pure W415, the smectic A* phase grows in from the isotropic state with the layer normal rotated ψ = - 24° from the rubbing direction, a consequence of the surface electroclinic tilt θs of the director. The sign of θs depends on the molecular handedness, with θs ≡ 0 in the racemate, and increasing linearly with moderate enantiomeric excess before saturating as ee → 1. A uniform layer structure can be achieved using cross-rubbed alignment layers, in which case thin cells of W415 in the smectic C* phase display V-shaped (analogue) electro-optic switching.

The forgotten liquid crystals of Daniel Vorlander: A new look at mesogenic 4-pyridones

Three classes of 4-pyridone (1H-pyridin-4-one) terminated liquid crystals were synthesized and their mesogenic properties examined. These liquid crystal classes differ in the composition of the aromatic core group which vary among azobenzene, stilbene or tolane groups. The synthesis of the 4-pyridones was accomplished by aromatic nucleophilic substitution reaction of the appropriate activated aryl fluoride with 4-hydroxypyridine. These pyridone liquid crystals possess broad enantiotropic nematic and smectic A phases and may possess useful properties such as high birefringence and polarity including hydrogen bonding capability. The original report of a 4-pyridone containing liquid crystal due to Vorlander has been substantiated.

High performance electroclinic materials

Abstract Many interesting potential applications of the electroclinic effect continue to drive new materials development. Herein we present recent results of a project aimed at obtaining improved electroclinic materials.

Chirality Detection with FLCs—a Comment

An interesting result, with some bearing upon recently discovered unichiral LCs obtained from putatively achiral or racemic molecules, is described. Specifically, the high P ferroelectric liquid crystal W314, when prepared from racemic 2-butanol purchased from Aldrich, gave unichiral FLC samples with negative P. This was shown to be due to a slight enantiomeric excess in the Aldrich racemate; authentically racemic W314 was obtained from freshly-prepared racemic 2-butanol. These results suggest that ferroelectric electro-optic behavior is an extremely sensitive detector of net chirality in near-racemates.

Synthesis and characterisation of laterally substituted noncentrosymmetric main chain hydrogen-bonded polymers

A series of laterally substituted noncentrosymmetric hydrogen-bonded liquid crystalline polymers which incorporate stilbazole acceptor units, alkyl or ethylene glycol linkers units, and benzoic acid or phenol donor units were prepared and investigated for their hydrogen bonding behaviour and phase transitions. Fourier transform infrared (FTIR) indicated that these polymers possess strong intermolecular donor–acceptor hydrogen bonding. These polymers have lower melting points than their non-substituted analogue, and some of the polymers are mesomorphic.

A new class of liquid crystals: methylene-1,4-dihydropyridines

A group of liquid crystal materials which contain the novel methylene-1,4-dihydropyridine substructure were synthesized and their mesogenic properties examined. Three main classes of liquid crystal compounds which differ in the structure of the aromatic core group (phenyl, azobenzene and diphenylacetylene) attached to the nitrogen of the 1,4-dihydropyridine group were studied. The synthesis of the methylene-1,4-dihydropyridine group was accomplished in excellent yield by a Knoevenagel condensation of a 4-pyridone intermediate with an active methylene compound. The liquid crystal materials prepared thus far which contain this methylene-1,4-dihydropyridine structure all possess broad enantiotropic smectic A phases and one example also possesses a tilted smectic C phase. These mesogens may possess useful properties such as high birefringence.

Hydrogen bonded liquid crystalline heterodimers incorporating alkoxystilbazoles and alkoxy-4-pyridones

The preparation and characterisation of a series of hydrogen bonded liquid crystalline dimers containing benzoic acid, alkanoic acid and phenol donors and alkoxy-stilbazole or alkoxy-4-pyridone hydrogen bond acceptors are reported. These heterodimers possess strong intermolecular donor–acceptor hydrogen bonding. The heterodimers, as well some of the individual components used in their preparation, possess liquid crystalline phases.

Peptide/Protein Separation with Cationic Polymer Brush Nanosponges for MALDI-MS Analysis

A cationic polymer nanobrush was synthesized, attached to a MALDI target, and used for the fractionation of peptides and proteins based on their pI, prior to analysis by MALDI-MS. The cationic polymer nanobrush was synthesized on a gold substrate by AIBN photoinitiated polymerization, using a 70:30 ratio of 2-aminoethyl methacrylate hydrochloride (AEMA):N-isopropylacrylamide (NIPAAM). This brush showed selectivity for adsorption of acidic peptides and proteins and allowed fractionation of simple two-component mixtures to be completed in less than 10 min. The brush-adsorbed biomolecules were recovered by treating the nanobrush with ammonium hydroxide, which effectively collapsed the brush, thereby releasing the trapped compounds for MALDI MS analysis. These results demonstrate that nanobrush can serve as a convenient platform for rapid fractionation of biomolecules prior to analysis by MALDI-MS.

Design of Polar Organic Liquid Crystalline Thin Films

We describe a strategy for the design of noncentrosymmetric organic thin films with thermodynamically stable polar order. We report the thermal and optical properties of a group of hydrogen bonding liquid crystalline (LC) monomers. The self-assembly of these LC materials could lead to improved polar stability and processibility yielding novel devices that utilize pyroelectricity, piezoelectricity, or second-order NLO properties.