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 T_NI 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 T_NI. 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.

An important aspect of modern materials science, namely the possibility of combining inorganic nanoparticles and liquid crystals in composite materials is discussed. These systems make it possible to combine liquid crystal properties of matrix and luminescent properties of quantum dots. A five-component mixture consisting mainly of 4-cyanobiphenyl derivatives used as a matrix. The substitution of ligands formed during the synthesis of quantum dots with derivatives of organic acids is shown. Using two new optically active ligands, the chiralization of the nematic matrix was demonstrated by introducing quantum dots into it.

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. В данной работе исследовано нелинейное поглощение инфракрасных (ИК) (1250 нм) фемтосекундных импульсов и возбуждаемая ими видимая фотолюминесценция (ФЛ) в жидко-кристаллических (ЖК) полимерных пленках с внедренными квантовыми точками (КТ) CdSe/ZnS типа «ядро–оболочка». Зависимость нелинейного пропускания от падающей интенсивности указывает на трехфотонное поглощение в пленках, при этом коэффициент поглощения трех фотонов для полимерного композита КТ–ЖК полимер сопоставим с этой величиной для объемного CdSe. Спектр ФЛ, возбуждаемой ИК-импульсами, совпадает со спектром однофотонной ФЛ. Зависимость сигнала ФЛ от мощности излучения ИК-лазера кубическая с последующим насыщением для спектрального диапазона 2,10–2,25 эВ, при этом интенсивность насыщения уменьшается для меньшей энергии фотонов ФЛ. Присутствие сигнала второй гармоники в спектре сигнала ап-конверсии приводит к его изменению с увеличением мощности возбуждения.

The stimulated assembly/disassembly of particles is a technique allowing for precise spatial and temporal control over the resulting structures to be realized. The application of a photosensitive liquid crystal (LC) allows the use of a photo-initiated order–disorder transition for the ordering and redistribution of dispersed nanoparticles. The semiconductor quantum dots (QDs) among them are useful for the imaging of such redistribution through simple luminescent microscopy with excitation by laser radiation at a wavelength of 532 nm. Doping the LC matrix with azo-chromophore molecules allowed us to localize the light-driven phase transition of the LC from the organized to the isotropic phase inside the spot, illuminated by ultraviolet (UV) light through a slit. The phase transition leads to a redistribution of the QDs within the matrix, followed by QD-rich region formation. After the termination of UV illumination, the QDs were found to form droplets in the region where UV illumination resulted in a homogeneous distribution of the QDs. The translation of the sample through the UV-illuminated spot resulted in QD accumulation inside the isotropic phase at the borders of the isotropic phase. The results obtained provide a good agreement with the model calculations of nanoparticle diffusion at the LC phase–isotropic liquid interface.