Design and synthesis of photosensitive 1D photonic system based on cholesteric liquid crystalline polymer will be presented. The photosensitivity and chirality is provided by a novel chiral hydrazone photochromic moiety covalently boud to the polymer backbone of a comb-shaped copolymer. Combination of the chirality and photosensitivity enabled reversible photomanipulation of the helical pitch of the supramolecular cholesteric structure resulting in material with a tunable selective reflection of circularly polarized light of the same helical sense as the chiral structure. In contrast to many other photochromic systems based on E-Z isomerization, the E and Z isomers of hydrazone photochromic group are kinetically stable that enable to achieve a pure photoinduced switch without any dark relaxation at any temperatures
We have studied several compounds of non-chiral mesogens composed of symmetrically and non-symmetrically bent-shaped
molecular core with thermally stable ester linkages and laterally substituted by methoxy group. Recently,
mesomorphic properties have been described and the SmCP (B2) phase has been identified in a wide temperature range
below the isotropic phase. Additionally, symmetrical bent-shaped mesogens exhibit the B7 phase on cooling from the B2
phase. Herein we concentrated on nonlinear optical properties in the observed mesophases. Second harmonic generation
(SHG) supports the idea that the ground state of the B2 phase in studied bent-shaped mesogens has antiferroelectric
character and demonstrates the switching from antiferroelectric to ferroelectric state under applied electric field.
Two binary mixtures have been studied of homologues from a series derived from 4-alkoxybiphenyl-4'-carboxylic acid with three chiral centers exhibiting ferroelectric (FE), antiferroelectric (AF) and tilted hexatic phases. One homologue exhibits a re-entrant SmC* (SmC*re) phase, which is miscible with the SmC* phase. The phase diagrams of the studied mixtures exhibit a close pocket of the SmC*A phase. The SmC*re phase is induced even in the mixtures composed from homologues without this phase. Dielectric spectroscopy reveals the Goldstone mode in both ferroelectric SmC* and the SmC*re phases, this mode being stronger when increasing concentration of the antiferroelectric homologue: In the SmC*A phase a relaxation mode is detected with the relaxation frequency three orders higher, which exhibits critical slowing down when approaching the SmC*re phase. This mode, which can be attributed to the anti-phase mode is responsible for the appearance of the SmC*re phase. In mixtures exhibiting the SmC*A phase a helix twist inversion occurs in the vicinity of the low temperature border of the AF phase.
Dielectric dispersion has been studied in the frequency range of 10Hz divided by 1MHz in liquid crystals with 2- alkoxypropriate chiral group. Two of them exhibit the spontaneous helix twist inversion in the SmC* phase. The dispersion reveals two modes, dielectric strengths as well as relaxation frequencies of which exhibit a strong dependence on the sample thickness. Mode 1 with the relaxation in the kHz range is the Goldstone mode, which is combined with a thickness mode, but it becomes the pure thickness mode in the temperature range near the helix twist inversion temperature, where the helicoidal structure is unwound. This situation is reflected in the temperature dependence of characteristics parameters of mode 1. The lower frequency mode 2 is attributed to a mode connected with a non-homogeneous distribution of ionic space charge, which is localized near the sample surface.
New series of ferroelectric liquid crystals derived form alkoxycinnamic acid containing chiral alkyllactate group was synthesized. All compounds have a wide temperature range SmC* phase at temperatures above 100 degrees C and high spontaneous polarization. Some of homologues exhibit spontaneous helix twist unwinding in the SmC* phase accompanied with the helix twist inversion.
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