Vitrified Chiral−Nematic Liquid Crystalline Films for Selective Reflection and Circular Polarization

Abstract

Nematic and left-handed chiral−nematic liquid crystals comprising methoxybiphenylbenzoate and (S)−(−)-1-phenylethylamine pendants to a cyclohexane core were synthesized and characterized. Although pristine samples were found to be polycrystalline, thermal quenching following heating to and annealing at elevated temperatures permitted the molecular orders characteristic of liquid crystalline mesomorphism to be frozen in the glassy state. Left at room temperature for 6 months, the vitrified liquid crystalline films showed no evidence of recrystallization. An orientational order parameter of 0.65 was determined with linear dichroism of a vitrified nematic film doped with Exalite 428 at a mole fraction of 0.0025. Birefringence dispersion of a blank vitrified nematic film was determined using a phase-difference method complemented by Abbé refractometry. A series of vitrified chiral−nematic films were prepared to demonstrate selective reflection and circular polarization with a spectral region tunable from blue to the infrared region by varying the chemical composition. The experimentally measured circular polarization spectra were found to agree with the Good−Karali theory in which all four system parameters were determined a priori: optical birefringence, average refractive index, selective reflection wavelength, and film thickness.

Novel Glassy Nematic Liquid Crystals for Non‐destructive Rewritable Optical Memory and Photonic Switching

“…Compounds I, II, and III were synthesized largely following literature procedures [14,17,18,25]. Chemical structures were elucidated with elemental analysis (performed by Quantitative Technologies, Inc.) and 1 H NMR (400 MHz, Avance-400, Bruker) spectroscopy.…”

“…Despite these promising results, there are still technical challenges remaining to be solved, such as sticking between stamp and polymer layer [13] and the influence of the viscoelastic behavior of the polymer on the imprinting results. [14] Therefore, it is very important to conduct research on many fundamental aspects of nanoimprint lithography. Further, the fabrication of stamps for nanoimprint lithography requires e-beam lithography, which limits the accessibility of the nanoimprint technique.…”

Glassy Liquid Crystal Films as Broadband Polarizers and Reflectors via Spatially Modulated Photoracemization

“…Current approaches to fabrication of NPR structures use inverted honeycomb frameworks, [8] hierarchical laminates, [9,10] open cell polymeric or metallic foams, [11] and mechanical devices made of hinges, springs, and sliding collars. [12] All of these structures consist of arrays of reentrant cells with cell dimensions larger than 1 mm; all contract under axial compression.…”

“…Using previously prepared precursor alcohols (S)-1-phenylethyl-4-[4-(2-hydroxyethoxy)benzoyloxy]benzamide and 2-(3-hydroxypropyl)-6-(4-cyanophenyl)naphthalene, [7,8] we synthesized I and II at a yield of 25 and 24 %, respectively, following the procedures reported elsewhere. [9] A bridged binaphthyl derivative, III, was synthesized following a literature procedure [10] with a 48 % yield. The molecular structures were elucidated with 1 H NMR spectroscopy and elemental analysis.…”

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

“…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.…”