Molecular orientational properties of a high-tilt chiral smectic liquid crystal determined from its infrared dichroism

Abstract

The orientational characterisitics and the temperature dependencies of the molecular apparent tilt angle of a partly fluorinated chiral smectic liquid crystal ͑/S/͒-4-͑1-methylheptyloxycarbonyl͒phenyl 4Ј-͓6-͑3,4,4,4-tetrafluoro-3-trifluoromethylbutylcarbonyloxy͒hexyloxy͔ biphenyl-4-carboxylate ͑acronym MH-PHFHHOBC͒ are studied using the polarized Fourier transform infrared ͑FTIR͒ spectroscopy. The molecular orientational distributions and the orientational order parameters for a homogeneously aligned liquid crystalline sample at various temperatures and external electric fields are examined. The analysis uses the dichroic parameters of the phenyl and the carbonyl bands. For a temperature range of 65-80°C corresponding to the antiferroelectric SmC A * phase, the molecular apparent tilt angle lies within the range 43°-44°; antiferroelectric smectic structure being rather close to the orthoconic SmC A * phase. An application of sufficiently high dc field across the cell in its SmA * phase surprisingly shows that the dichroism first increases slowly and then rapidly in two stages and finally a saturated apparent tilt angle of ϳ30°is reached. The IR dichroic data is used to estimate the polar angles and the degree of rotational biasing of the carbonyl groups with respect to the molecular long axis. In the SmA * phase, the sample appears to demonstrate some of the typical properties of a de Vries material.

Transition Moment Orientation Analysis on a Smectic C Liquid Crystalline Elastomer film

“…The latter is, however, more important, because it can be related to the molecular structure in a straightforward way. Measurements in transmission geometry can more easily provide information concerning the molecular orientation (e.g., liquid crystals);; thus, it enables one to quantify the orientation distribution of different molecular groups. , Polarized IR spectroscopy (for a review see Griffiths and Haseth) is commonly applied using several assumptions, most importantly the rotational symmetry of the orientation distribution with respect to its main axis lying on the sample plane, that allows to limit the variation of the electric field in the sample plane only.…”

Propagation of an electromagnetic wave in an absorbing anisotropic medium and infrared transmission of liquid crystals: Comparison with experiments

“…The compound with the chemical name ͑/S/͒-4-͑1-methylheptyloxycarbonylphenyl-4Ј-͓6-͑3,4,4,4-tetrafluoromethylbutylcarbonyloxy͒hexyloxy͔͒ biphenyl-4carboxylate and an acronym of MHPHFHHOBC ͑laboratory name AH43͒, ͑chemical formula given in Ref. ͓11͔,Fig. 1͒ was synthesized with a partly fluorinated achiral tail in the laboratory of Goodby.…”