NMR Study of Molecular Configuration and Order in a Fluorinated-Liquid–Crystalline Schiff Base

Abstract

Articles you may be interested inDirect observation of the substitution effects on the hydrogen bridge dynamics in selected Schiff bases-A comparative molecular dynamics study Orientational order in a liquid crystalline mixture studied by molecular dynamics simulation and NMRThe fluorine and proton spin resonances in the nematic-liquid-crystal state of terephthalbis(aminofluorobenzene) are studied using the method of moments. The second moment of the proton line has a large dependence on the molecular configuration as well as on the degree of molecular order. The fluorine second moment, on the other hand, has a negligible dependence on the configuration and is used to obtain a measure of the order. With the degree of order known, the second moment of the proton resonance is used to examine possible configurations the molecule may follow. The results rule out the possibility of a planar molecule as well as a molecule in which the aromatic rings and the -N=CH-linkage groups are allowed to rotate around their bonds in an unhindered fashion. Best agreement with the data is found for the case where the plane containing the linkage group makes a preferred angle near 20° relative to the plane of the terminal aromatic rings. The temperature dependence of the proton spectrum is also interpreted in terms of the molecular order.

Molecular conformational changes in the smectic C, smectic A and nematic phases of TBBA

“…At this point it is interesting to note that the result that the Schiff base molecules in nematic phases are non planar, seems to be general. It has indeed been shown by proton NMR that the dihedral angle between the azomethine group and the aniline ring (external ring in our notation) are about 20°, 47°a nd 430 in terephtal bis (4-aminoflurobenzène) [17], MBBA [18] and EBBA [19], respectively. For TBBA, it has also been shown that this angle is relatively large [9].…”

Physics of liquid crystals

“…The XMR spectrum under low resolution is a single broad line, and the method of moments has been used to analyze the spectrum (Lippmann and Weber, 1957;Bravo et al , 1969) . The second moment, (A~,2), of the NMR spectrum for nuclear species i resulting from dipole -dipole interactions The first sum is over all the .…”

Spectroscopy of Liquid Crystals

“…The proton and fluorine magnetic resonance spectra of terephthalbis(aminof1uorobenzene) have been studied in the nematic phase [237]. only on the order parameter S. On the other hand, the proton resonance depends on the molecular configuration as well as on S. The PMR peaks have been assigned by comparison with the spectra of bis(4-chlorophenyl) terephthalate and terephthal bis(2-amino-5-chloropyridine) in the nematic phase.…”