Synthesis of Novel Glass-Forming Liquid Crystals Containing Acrylic Acid Trimer Core Unit and Mesogenic Moiety, and Their Use in Cholesteric Reflection Films

Abstract

ABSTRACT:A novel medium molecular mass liquid-crystalline (LC) material to form glassy nematic phase has been developed to provide uniformly aligned LC films. The LC material consists of an acrylic acid trimer as a core structure and a mesogenic moiety. The resulting LC trimer showed a nematic LC phase and vitrified to form monodomain films at room temperature. This glassy LC trimer is miscible with a chiral photochromic dopant, providing monodomain, aligned, defect-free cholesteric reflection films, the color of which is tunable by UV irradiation. 2 The degree of freedom of molecular motion is limited on losing fluidity by providing a high molecular weight or a crosslinked structure, and the helical molecular order is fixed.Glass-forming liquid crystals with a high glass transition temperature, such as LC polymers, can be aligned at elevated temperatures and then stabilized by cooling below their glass transition temperatures. However, LC polymers often do not undergo fast, defect-free alignment because of their entangled molecular chains.A good method for preparing birefringent films with complex optical functions is based on the photo-polymerization of reactive liquid crystals.3-5 These liquid crystals are aligned in the desired configuration in the monomeric state due to their low viscosities, and are subsequently converted into solid films through UV polymerization. Such birefringent films made with low molecular weight LCs, however, are not stable before UV irradiation because of crystallization at room temperature.For many optical and photonic applications, glassforming LCs represent a unique class of advanced materials that are capable of freezing the liquid-crystalline order into a solid state without crystallization. In a recent series of papers, a new molecular design concept, wherein nematic and chiral groups are chemically bonded to a volume-excluding core to prevent crystallization upon cooling, has been detailed. [6][7][8][9][10][11][12] These materials, however, were prepared using a multiple synthetic step and/or troublesome workup procedures. For the applications described above, materials with the highest possible glass transition temperature are needed to ensure sufficient room temperature stability of the devices. Another requirement is that the materials possess a broad nematic liquid crystal mesophase above their glass transition temperatures. Higher ordered mesophases, such as a smectic phase, are not preferred because of the difficulty in obtaining mono-domain films of these phases. 13In this paper, we present the design, synthesis and characterization of a novel medium molecular mass nematic liquid crystal (LC trimer), consisting of an acrylic acid trimer as the core structure and cyanobiphenyl benzoate as a mesogenic moiety. The LC trimer has an elevated glass transition temperature and exhibits both nematic and cholesteric phases with the addition of a chiral dopant.

Synthesis and Characterization of Cholesteric Thermotropic Liquid Crystalline Polyesters Based on Isosorbide

“…Cholesteric liquid crystalline polymers (ChLCPs) have ability to produce supermolecular structures characterized by a helical organization with certain identity period. This special organization is responsible for unique optical properties of cholesteric polymer liquid crystals such as selective reflection of light at different wavelengths, very high optical activity, high sensitivity of selective reflection of light to temperature variations and to the action of external electrical and magnetic fields [1][2][3][4][5]. The requirement of principal condition to develop a cholesteric phase is associated with the presence of an chiral (asymmetric) center in monomer which produces a heli-cal supermolecular structure [6].…”