In this paper, we studied nonlinear absorption of infrared (IR) (1250 nm) femtosecond pulses and visible photoluminescence (PL) excited by them in liquid-crystal (LC) polymer films with embedded CdSe/ZnS core-shell type quantum dots (QDs). The dependence of nonlinear transmission on incident intensity indicated three-photon absorption in the films, with the three-photon absorption coefficient for the QD-LC polymer composite comparable with the one for bulk CdSe. The spectrum of PL excited by IR pulses coincides with one-photon excited PL spectrum. Dependence of the PL signal on the IR laser radiation power is cubic with further saturation for the spectral region from 2.10 to 2.25 eV, with saturation intensity decreasing with lower PL photon energy. The presence of the second-harmonic signal in the up-conversion spectrum results in its variation with an excitation power increase.

We present an analysis of the 'order-disorder' phase transition into the liquid crystal matrix containing photochromic molecules with a small amount of semiconductor quantum dots (QDs). The factors studied are the influence of the chemical structure of azochromophores introduced in a liquid crystal (LC) on the phase behaviour and dielectric properties of the resulting composites as well as the life-time of the isotropic phase after photoinduced phase transition. We have chosen two azochromophores with different melting points Tm and degrees of branching. The branched structure of one chromophore promotes an increase in the life-time of Z-conformation and the corresponding stabilisation of the isotropic phase. The main factor influencing the increase in the life-time is a weaker intermolecular interaction between the LC matrix and the chromophore molecules. QDs in small amounts (0.5 and 1 wt.%) have a significantly smaller impact on the phase transition.

The structure and properties of the new material derived from binol (BCA), multifunctional chiral additive to liquid crystals (LC) with a high optical activity and the presence of free carboxylic groups in the molecule, are studied. The analysis of the thermal behavior of BCA is done by means of DSC, rheology methods, dielectric, and IR spectroscopy. The agreement between the rheological and dielectric data indicates the similar relaxation mechanisms, described within the WLF model. The analysis of the IR spectra proves the change in dielectric and rheological parameters induced by the variation in the structure of associates of hydrogen-bonded complexes. The modification of the sizes and quantity of the connected structures with the temperature may result in the possible appearance of nonlinear effects in LC composites associated with the simultaneous complex change in the dielectric and rheological properties.

We have synthesized and studied three new chiral substances as additives to a nematic liquid crystal. The difference in the optical activity and chemical structure of additive molecules results in the appearance of the chiral nematic phase and the change in both the compatibility of the mixture components and temperature range of the liquid crystal phase. The role of additives with fundamentally different structures and optical activities is shown. The increase in the TNI that is observed in mixtures with 4-[(2S)-(+)-2-Methylbutoxy]benzoic acid indicate the possibility of the increase in order caused by the formation of molecularly rigid and elongated dimers of the additive, which was confirmed using infrared spectra. The doping of the nematic liquid crystal with (2R)-(+)-2-[4-[2-Chloro-4-(4-hexylphenyl)phenyl]phenoxy]propanoic acid causes the lowering of TNI. The binol derivative S-(+)-6-[1-[2-(5-Carboxypentoxy)naphthalen-1-yl]naphthalen-2-yl] oxyhexanoic acid has the highest chirality among the additives used. One can explain the effects observed in terms of the role of size, shape, and compatibility with the nematic matrix as shown by the molecules that are used as additives.

Embedding quantum dots (QDs) into an organic matrix of controllable order requires the identification of their structural characteristics. This analysis is necessary for the creation of anisotropic composites that are sensitive to external stimuli. We have studied the QD structures formed during the single-step synthesis of CdSe/ZnS QDs and their transformations after the initial ligand's substitution for another ligand. This single-step process leads to the formation of the core/shell structure. We detect the presence of two oleic acid residues ionically connected to Zn and Cd. At the same time, the amount of Cd oleate at the surface is very small. We observe the ligand exchange process at the surface of the core/shell QDs. The oleic acid residues are substituted by terphenyl-containing (TERPh-COOH) aromatic acid residues. The reaction between CdSe/ZnS carrying TOP and oleic acid residues ionically bound with QDs and terphenyl-containing acid leads to the coexistence of multiple ligands on the QD surface at a ratio of 11:6:33 for TOP/OA/TERPh-COOH.

Nanocomposites based on CdSe or CdSe/ZnS quantum dots (QDs) and poly(methyl methacrylate) (PMMA) of different molecular weights and functionality were synthesized by ligand exchange of oleic acid with RAFT-based PMMA. The successful ligand exchange was confirmed by dynamic light scattering in combination with the approach "macromolecules-ghosts" and transmission electron microscopy. Comparative study of mono- and telechelics of PMMA revealed the similarities and differences in their behavior in formation of complexes with QDs and the optical properties of the corresponding nanocomposites. Telechelics exhibited higher efficiency in the complex formation and seemed to be promising candidates for the construction of devices based on QDs and polymer matrix for optical applications.

We report on effects of the matrix on photoluminescence spectra and lifetime and efficiency of up-conversion of core-type CdSe and core/shell CdSe/ZnS quantum dots embedded into smectic and amorphous polymers.