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The long-range orientational order of liquid crystals from homologous series of 4-n-alkyl-4 -cyanobiphenyl, 4-n-alkoxy-4 -cyanobiphenyl, trans-4-n-alkyl(4 -cyano-phenyl)-hexane, and 4-(trans-4 -n-alkylcyclohexyl)--isothiocyanato-benzene was studied by means of classical methods of optical spectroscopy: absorption of the polarized light, fluorescence depolarization, and Raman scattering depolarization. The absorption, emission, and Raman scattering spectra of linearly polarized light were recorded as a function of temperature in the whole range of the mesophase. On the basis of these spectra the order parameters P2 and P4 as well as the orientational distribution function were determined. The results obtained for members of various series with the same number of carbon atom in the alkyl chain were compared. It was found that the orientational order of liquid crystal molecules depends on the structure of the rigid core, on the kind of the terminal group as well as on the alkyl chain length. The odd-even effect for the order parameters, explained as the alteration of interaction between alkyl chains, was observed.

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One of the most important drawback of organic dyes is their low photo-stability which reduces possibility of their commercial utilization. In this article we employ the strategy of dye re-crystallization from oversaturated matrix in order to enhance material’s durability. One of the main advantages of perylene derivative is ability to form emissive j-aggregates, good miscibility and incorporation into liquid crystalline matrix. Investigation of perylene-based dye and LC matrix brought as the result very efficient light amplification modulation by applied external electric field. In our article we show that Stimulated Emission (STE) is possible to achieve from perylene-derivative based system, at typical fluence thresholds for laser dyes: 3.9 mJ/cm2. Moreover, presented system proves ultra-high photostability, showing lack of STE reduction even after 12 000 excitation laser pulses. Furthermore, we proved the possibility of light emission intensity control using external electric field.

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