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2 Opto-Electronics Review

2 2008

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Intermolecular interactions in Langmuir-Blodget films of liquid crystalline perylene derivatives

100%

Hertmanowski R. , Martyński T. , Stolarski R. , Bauman D.

tom Vol. 16, No. 3

237-243

Langmuir-Blodgett (LB) films formed of some discotic liquid crystals, namely 3,4,9,10-tetra-(n-alkoxy-carbonyl)-perylenes, mixed with arachid acid have been studied. The absorption and fluorescence spectra were recorded. The results obtained have led to conclusions about formation of self-aggregates of dye molecules both in ground and excited states at the air-solid substrate interface. It was found that some fraction of J-aggregates can be created in the ground state. In the excited state, mostly excimers appear and the number of this kind of aggregates depends on the length of the alkyl chains substituted to the perylene core, as well as on the dye concentration and the number of layers in LB films.

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

100%

Bauman D. , Zięba A. , Mykowska E.

tom Vol. 16, No. 3

244-250

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.