Alexi K. Nedeltchev

Synthesis and characterisation of thermotropic liquid-crystalline properties of azomethine dimers

A series of azomethine dimers were prepared by condensation reactions of benzaldehyde, biphenylcarboxaldehyde and 9-anthraldehyde with various aromatic diamines of varying flexibility in ethanol in the presence of tosic acid. Their chemical structures were determined by Fourier transform infrared and 1H and 13C nuclear magnetic resonance (NMR) spectroscopies, as well as elemental analysis. Their thermal properties were also examined by using a number of experimental techniques, including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarising optical microscopy (POM) and variable temperature X-ray diffraction (VTXRD). Azomethine dimer, prepared from benzaldehyde and 1,9-bis(4-aminophenoxy)nonane, exhibited a monotropic, nematic liquid-crystalline (LC) phase. The majority of the azomethine dimers containing biphenyl moieties exhibited enantiotropic, nematic LC phase on melting at relatively low temperatures, since they developed typical Schlieren, threaded or marbled textures in their LC phase. They also had accessible isotropisation temperatures well below their decomposition temperatures. Azomethine dimers containing anthracene moieties did not exhibit LC properties, but exhibited polymorphism as determined by POM and VTXRD in two cases. All of these azomethine dimers in the series had excellent thermal stability that was in the broad range of temperatures of 307–400°C depending on their degrees of aromaticity index.

Solution, thermal and optical properties of new poly(pyridinium salt)s derived from bisquinoline diamines

Several novel poly(pyridinium salt)s with heterocyclic bisquinoline moieties having both tosylate and triflimide counterions were prepared by either ring-transmutation or metathesis reaction. Their chemical structures were established by using 1H and 13C NMR, FTIR and elemental analysis. Their number-average molecular weights (Mn) ranged from 53,000 to 79,000 and their polydispersities ranged from 1.30 to 3.24 as determined by gel permeation chromatography. They had excellent thermal stabilities in the temperature range of 336–447 °C and glass transition temperatures in the range of 119–174 °C. They had good solubilities in common organic solvents and in several cases their critical concentrations (*C) were exceeded to form lyotropic liquid-crystalline phases. Additionally, they emitted light in the blue and green region in both solution and solid state. Their quantum yields were also determined by using a spectrofluorometer.

Design and synthesis of photoactive ionic amorphous molecular materials

Compounds bearing electrostatic charges have unique properties including outstanding ionic-conductivity when compared with neutral ones. On the other hand, amorphous molecular materials harness the advantages of small molecules with high purity, defined structures and monodispersity, while still being easily processable into thin films and fibers. Here, we report a series of bis(pyridinium salt)s that combine these properties to form ionic amorphous molecular materials. Their design allowed them to vitrify efficiently upon slow cooling. They exhibited glass-transition temperatures in the range of 81–191 °C and had excellent thermal stabilities of up to 461 °C. Fibers were easily drawn from their melts that were visible to the naked eye. Although they were completely conjugated and had large molecular sizes, they were soluble in many common organic solvents. Additionally, they fluoresced blue and green light in both solution and solid states. They could be useful for high-performance applications in opto- and microelectronic fields, among others.

Synthesis, thermal and lyotropic liquid crystalline properties of protic ionic salts

A series of protic ionic salts were synthesised by a simple acid–base reaction from various pyridine derivatives and dodecylbenzenesulfonic acid in a common organic solvent and characterised in terms of their thermal and lyotropic liquid crystalline properties using various experimental techniques. All of them exhibited lyotropic liquid crystalline phases in toluene, methanol, acetonitrile, dimethyl sulfoxide and water. Their critical concentrations for the formation of biphasic solutions and concentrations for the formation of lyotropic solutions were quite broad depending on the dielectric constants of the solvents. Their lyotropic phases were identified as lamellar phases, since their textures exhibited bâtonnets, oily streaks and mosaic textures. They can potentially be used for many organic transformations, which may have implications in green chemistry.

Synthesis, Thermal, and Light-Emitting Properties of Anthracene Derivatives

Several anthracene derivatives were prepared by a single-step reaction and characterized their thermal properties by differential scanning calorimetry (DSC) and thermogravimetric analyses. Their photoluminescence properties were examined in a large number of organic solvents of increased polarity that included toluene, chloroform, tetrahydrofuran, acetone, methanol, acetonitrile, and dimethyl sulfoxide. Some compounds exhibited emission spectra with vibrational fine structures in organic solvents; and other compounds exhibited structureless emission spectra in organic solvents.