Orientational Behaviour of the Guest-Host Systems in the Smectic A and Nematic Phases

Abstract

The measurements of the polarized absorption and fluorescence components spectra for the guest-host mixtures have been used to study the long orientational order in the uniaxial phases of the liquid crystal. The temperature dependence of the order parameters, (Ρ2) and (Ρ 4 ), has been investigated and the molecular distribution function has been determined. On the basis of the (Ρ2) and (Ρ4), values some conclusions about the molecular orientation in the smectic A and nematic phases of the liquid crystalline samples have been drawn. It has been also found that the fluorescence spectroscopy is a sensitive method for determination of the phase transition temperatures of the liquid crystal doped with the fluorescent dye.

Spectral and orientational properties of new group of naphthalene derivatives of bicarboxylic acid in liquid crystal 7CB

“…Table 6 it is seen that the order parameter <P 2 > obtained from the absorption measurements for a given dye/7CB mixture and at a given temperature is very similar to that determined from fluorescence measurements. Moreover, <P 4 > F parameter is always positive, in contrary to the previously obtained negative values of it for some dye/liquid crystal mixtures in the nematic phase [13,[17][18][19][20]22,23]. This means that, when introducing in calculations the appropriate values of the angles between the long molecular axis and the absorption and the emission oscillators, it is possible to obtain the results which are consistent to each other and which are in agreement with the theories of the nematic phase [24,25].…”

“…The results obtained are gathered in Table 6. However, 7CB is in the nematic phase at a room temperature and our experience [13,[17][18][19][20] indicates that in this phase the condition t R >> t F is only approximately valid, thus enabling only a rough estimation of the transition moments directions. We compared additionally the values of <P 2 > obtained from the polarized absorption measurements at a room temperature for 7CB doped with dyes 1-12 to the ones for 7CB doped with dimethylamino-nitrostilben (DANS) [21].…”

Molecular Orientation in Uniaxial Liquid Crystal Phases as Studied by Electron Paramagnetic Resonance

“…6. The temperature dependence of the order parameter (Pi) for 8CB determined from the EPR spectra of 1 (squares), the optical birefringence (crosses) [19] and the polarized absorption spectra of the dichroic dye (circles) [22], T* Fig. 7.…”

Molecular Orientation and Odd-Even Effect in Nematogenic Homologous Series of 4-Cyanophenyl-4′-N-Alkylbenzoate

“…The naphthalene derivative of bicarboxylic acid (NDBA) was used as a fluorescent probe. NDBA is known as a dye of high orientation ability in the liquid crystalline matrices [11,14]. The molecular structure of dyes is shown in Table 1.…”

“…The details of this setup were described in [16]. The fluorescence spectra were recorded in B geometry, i.e., the exciting light beam was perpendicular to the cell surface and the fluorescence light was monitored perpendicularly from the same side of the cell [14,17]. On the basis of fluorescence intensity values, the emission anisotropies, R 1 and R 2 were calculated in the following way:…”