Orientational behaviour of some homologues of 4-n-pentyl-phenylthio-4'-n-alkoxybenzoate doped with dichroic dye

The long-range orientational order of three members of 4-n-pentylphenylthio-4'-n-alkoxybenzoate (nS5) series doped with a dichroic dye was studied by means of electronic absorption and fluorescence measurements. The order parameters and as well as the orientational distribution function were determined on the basis of absorption and emission spectra of linearly polarized light recorded as a function of temperature in the nematic, smectic A, and smectic C phases. An influence of the dye molecular structure on the orientational order of the dye/liquid crystal mixture was observed. Moreover, the dependence of the order parameter values on the length of the alkoxy chain in liquid crystal molecules was found. It was shown that the order parameter , obtained from fluorescence measurements, can be helpful in recognizing the second-order or weakly first-order transitions between various liquid crystalline phases.