No abstract

Alkaline earth lead zinc phosphate glasses doped with Mn(II) are characterized by spectroscopic techniques like X-ray diffraction (XRD), UV-visible, differential scanning calorimetry (DSC), electron paramagnetic resonance (EPR), Fourier transform infrared (FTIR) and Raman. Optical absorption spectrum exhibits four bands which are characteristic of Mn(II) in distorted octahedral site symmetry. The crystal field parameter Dq and Racah interelectronic-repulsion parameters B and C have been evaluated. All investigated samples exhibit EPR signals which are characteristic to the Mn 2+ ions. The shapes of spectra are also changed with varying alkaline earth ions content. FTIR spectra show specific vibrations of phosphate units. The characteristic Raman bands of these glasses due to stretching and bending vibrations were identified and analysed by varying alkaline earth content. The intensity and frequency variations for the characteristic phosphate group vibrations have been correlated with the changes of the structural units present in these glasses. Depolymerization of the phosphate chains in all the glasses is observed with replacement of alkaline earth content by spectroscopic studies. This leads to a strong decrease of the average chain length and a small decrease of the average P-O-P bridging angle with replacement of alkaline earth content.

No abstract

No abstract

No abstract

No abstract

No abstract

IntroductionSupramolecular liquid crystals, obtained through hydrogen-bonding of complementary molecules, have extensively been investigated in recent years. Following the well-established examples of liquid crystal formation through dimerization of aromatic carboxylic acids [1,2], several classes of compounds have been reported, including conventional liquid crystals [3][4][5][6][7][8][9], supramolecular polymer networks [10][11][12][13], and ferroelectric liquid crystals [14][15][16][17] formed by the interaction of complementary molecules, the liquid crystalline behaviour of which is crucially dependent on the structure of the resulting supramolecular system. It is now well-established that for the formation of liquid crystalline materials through hydrogen bonding, the complementarity of the interacting components coupled with the directionality of the hydrogen bonds are the main (but not the only) factors contributing to liquid crystallinity [18]. In fact, it has been widely accepted that the proton donor and acceptor capabilities of the atoms of the functional groups involved in the hydrogen bonding contribute remarkably to the occurrence of new phases and their thermal stability. Despite their low bond activation energies, these non-covalent interactions show a profound impact on thermal and physical properties such as melting points, heats of vaporization, mesomorphic behaviour, etc.In continuation of our systematic investigation of Hbonded liquid crystals comprising different proton and acceptor groups [19][20][21][22][23], the present communication deals with the synthesis and phase behaviour of a new series of liquid crystalline systems involving intermolecular hydrogen bonding between p-n-alkoxybenzoic acids (nABA) and p-aminobenzonitrile (ABN). The molecular structure of the ABN:nABA series is represented in Figure 1. New liquid crystalline compounds involving intermolecular hydrogen bonding between mesogenic p-n-alkoxybenzoic acids (nABA) (where n denotes the alkoxy carbon number varying from propylto decyl-and dodecyl-) and p-aminobenzonitrile (ABN) are synthesized. The thermal and phase behaviour of these materials is studied by Thermal Microscopy and Differential Scanning Calorimetry. A detailed IR spectral investigation in solid and solution states confirms the formation of H-bonding between cyano and -COOH groups of ABN and nABA, respectively. Comparative thermal analyses of both free p-n alkoxybenzoic acids and H-bonded complexes suggest the induction of smectic-G phase in all the complexes.