Infrared spectroscopic study of molecular hydrogen bonding in chiral smectic liquid crystals
We report the use of Fourier-transform infrared (IR) spectroscopy to probe intermolecular and intramolecular hydrogen bonding in thermotropic liquid-crystal phases. Infrared spectra of aligned smectic liquid crystal materials vs temperature, and of isotropic liquid-crystal mixtures vs concentration were measured in homologs both with and without hydrogen bonding. Hydrogen bonding significantly changes the direction and magnitude of the vibrational dipole transition moments, causing marked changes in the IR dichroic absorbance profiles of hydrogen-bonded molecular subfragments. A GAUSSIAN94 computation of the directions, magnitudes, and frequencies of the vibrational dipole moments of molecular subfragments shows good agreement with the experimental data. The results show that IR dichroism can be an effective probe of hydrogen bonding in liquid-crystal phases.
Jang
WG
Ferroelectric Liquid Crystal Materials Research Center, Department of Physics, University of Colorado, Boulder, Colorado 80309-0390, USA.
Park
CS
Kim
KH
Glaser
MA
Clark
NA