White lasers are becoming increasingly relevant in various fields since they exhibit unprecedented properties in terms of beam brightness and intensity modulation. Here we show that in hybrid materials based on modified and/or dye-doped liquid crystals, white laser light can be effectively generated upon optical pumping. We demonstrate a multicolor stimulated emission phenomenon obtained in dye-doped, liquid crystalline systems or in a multifunctional phase-separation system based on polymer matrix encompassing liquid crystals and multiple organic chromophores, where the precise color adjustment can be provided by applying the external electric DC fields or pumping energy density. The use of liquid crystalline materials for laser light generation can bring several advantages, like better photostability comparing to polymeric lasers, easy tunability of emitted light, e.g., by applied of the electric field, low cost of fabrication, and multitude of randomly or precisely generated photonic structures, which can be controlled by the external fields.
Langmuir-Blodgett (LB) films formed of some discotic liquid crystals, namely 3,4,9,10-tetra-(n-alkoxy-carbonyl)- perylenes, have been studied. The absorption and fluorescence spectra were recorded. The results obtained have led to conclusions about formation of dimers both in ground and excited states at the air-solid substrate interface. Moreover, information about the molecular arrangement in LB films has been obtained.
Langmuir and Langmuir-Blodgett films of various dyes, namely derivatives of: 3,4,9,10-perylenetetracarboxylic acid, 3,4,9-perylenetricarboxylic acid, naphthalenebicarboxylic acid and naphthoylenebenzimidazole as well as of their mixtures with a liquid crystal were investigated. The dependence of the surface pressure -- on the mean molecular area for Langmuir films was measured, from which the molecular organization and the miscibility of components in the monomolecular layer at the air-water interface were determined. For Langmuir-Blodgett films the absorption and emission spectra were recorded and information about the spectral properties and molecular alignment of dyes and liquid crystals in ultrathin layers at solid substrates was obtained.
Langmuir (L) and Langmuir-Blodgett (LB) films of perylene-like dye and its binary mixtures with 4-octyl-4'-cyanobiphenyl (8CB) and 4-pentyl-4"-cyano-p-terphenyl (5CT) have been investigated. On the basis of the surface pressure-mean molecular area isotherms, the molecular organization on the air-water interface has been determined. The spectroscopic study of the LB films has allowed conclusions to be drawn about the alignment of the molecules on the quartz slides. The absorption and fluorescence spectra of the LB films of the perylene-like dye have revealed the formation of self-aggregates.
Surface pressure-mean molecular area isotherms of Langmuir films of some liquid crystals with CN or --NCS terminal group as well as of their binary mixtures have been recorded. It was found that only the liquid crystals which molecules have CN group are able to form a stable monolayer at the air-water interface. Information about the molecular organization and intermolecular interaction in two dimensional layer has been obtained. Moreover, the miscibility or phase separation of two components in the mixtures of various compositions has been determined by using excess area criterion and surface phase rule.
Results of the thermodynamic study of the molecular interaction in Langmuir films of mixtures of 4-n-octyl-4'- cyanobiphenyl (8CB) and 4-pentyl-4'-cyanoterphenyl (5CT) are presented. Both mixed materials are thermotropic liquid crystals and as a single component material is able to form a monolayer at the air-water interface. We demonstrate the effect of interaction of two similar liquid crystal molecules and how the surface pressure is affected by mixing the components in different mole fractions. The surface pressure-area isotherms indicate that 8CB and 5CT are immiscible in whole mole fraction range.
The order parameters of some dichroic fluorescent dyes (naphthalene derivatives of bicarboxylic acid) in nematic liquid crystal matrices have been determined. The influence of the dye addition on the clearing temperature of the nematic host has been investigated. It has been found that the dyes studied can be utilized in the guest-host liquid crystal displays working both in passive and active modes.
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