215 research outputs found
Precise orientation control of a liquid crystal organic semiconductor via anisotropic surface treatment
No full textWe report a three-dimensional (3D) molecular orientation control of a liquid crystal organic semiconductor (LC-OSC) based on the long-range ordering characteristic of an LC material. To this end, a synthetic LC-OSC molecule, MeOPh-BTBT-C8, with a fluidic nematic (N) phase that is essential for alignment control over a large area and a smectic E (SmE) phase showing high ordering, was prepared. A simple flipping of a sandwich cell made of the LC-OSC material between the top and bottom substrates that have uniaxial-planar degenerated alignment as well as crossed rubbing directions responds to the given surface anchoring condition and temperature gradient. Optical observation of the alignment-controlled LC-OSC was carried out by polarized optical microscopy (POM), and the corresponding charge carrier mobility was also measured by fabricating organic field-effect transistors (OFETs). Our platform offers a facile approach for multidirectional and multifunctional organic electronic devices using the stimulus-response characteristics of LC materials
Structure-Property Relationships For Nanophase Segregating Groups In SmAP Mesogens
No full textThe SmAPF liquid crystal phase of the bent-core mesogen W586 represents the first reported orthogonal ferroelectric liquid crystal material, designed and prepared in the Walba group, characterized by the Clark group, and first reported in Science in 2011. The design of W586 involved the introduction of a strongly nanophase segregating group terminating the “tail” of an antiferroelectric SmAPA mesogen published by the Sadashiva group. The SmAPF phase demonstrates interesting and potentially useful electro-optic properties, including fast phase-only electrooptic modulation of light, with analog V-shape switching with optical latching. Since the synthesis of W586, the Walba group has continued the study of the SmAPF phase through the synthesis of a variety of isomers, homologs, and derivatives of W586, designed to elucidate structure-property relationships for formation of the phase, and allowing for the design of materials with properties tuned for specific applications. This work revealed a dramatic ferroelectric-antiferroelectric odd-even effect, where homologs of W586 with an odd number of methylene groups in the mesogen tail separating the core and the nanophase segregating tail terminus exhibit the SmAPF phase, while even numbered tails exhibit the SmAPA phase, though the nanophase segregating groups themselves remain identical.
Here we report the synthesis and study of new classes of SmAP mesogens which vary the nanophase segregating groups. The new mesogens involve two distinct classes of materials: first involving changes in the structure of the carbosilane nanophase segregating group found in W586, and second, materials possessing polyfluorioinated oligoethylene glycol (PFOEG) tails as the nanophase segregating group in SmAP mesogens. The latter was first reported by Korblova et al. in a system with a very different bent core. In the process, it was discovered that the antiferroelectric SmAPA phase can also exhibit V-shaped switching. This unexpected and remarkable phenomenon is shown to result from the formation of a kinetically trapped SmAPF state after initial application of an electric field.</p
Structure-Property Relationships For Nanophase Segregating Groups In SmAP Mesogens
No full textThe SmAPF liquid crystal phase of the bent-core mesogen W586 represents the first reported orthogonal ferroelectric liquid crystal material, designed and prepared in the Walba group, characterized by the Clark group, and first reported in Science in 2011. The design of W586 involved the introduction of a strongly nanophase segregating group terminating the “tail” of an antiferroelectric SmAPA mesogen published by the Sadashiva group. The SmAPF phase demonstrates interesting and potentially useful electro-optic properties, including fast phase-only electrooptic modulation of light, with analog V-shape switching with optical latching. Since the synthesis of W586, the Walba group has continued the study of the SmAPF phase through the synthesis of a variety of isomers, homologs, and derivatives of W586, designed to elucidate structure-property relationships for formation of the phase, and allowing for the design of materials with properties tuned for specific applications. This work revealed a dramatic ferroelectric-antiferroelectric odd-even effect, where homologs of W586 with an odd number of methylene groups in the mesogen tail separating the core and the nanophase segregating tail terminus exhibit the SmAPF phase, while even numbered tails exhibit the SmAPA phase, though the nanophase segregating groups themselves remain identical.
Here we report the synthesis and study of new classes of SmAP mesogens which vary the nanophase segregating groups. The new mesogens involve two distinct classes of materials: first involving changes in the structure of the carbosilane nanophase segregating group found in W586, and second, materials possessing polyfluorioinated oligoethylene glycol (PFOEG) tails as the nanophase segregating group in SmAP mesogens. The latter was first reported by Korblova et al. in a system with a very different bent core. In the process, it was discovered that the antiferroelectric SmAPA phase can also exhibit V-shaped switching. This unexpected and remarkable phenomenon is shown to result from the formation of a kinetically trapped SmAPF state after initial application of an electric field.</p
Orientation control over bent-core smectic liquid crystal phases
No full textBent-core smectic liquid crystal (LC) phases (B phases) have been widely studied since their unusual polar and chiral properties were discovered in the 1990s. Relatively few studies have examined the mechanisms by which the orientation of the B phase may be controlled to produce the type of macroscopic domain that is essential for organic semiconductor, optical device and patterning applications. This review is intended to cover recent progress towards controlling the B phases upon layering, including anisotropic treatment methods and topographical confinement methods. Finally, this review closes with a discussion of B smectic phases that have been fabricated for use in certain applications
Extreme nanoseparation by dual-confining effect : Binary mixtures of bent core and rod-like liquid crystals in confined geometry
No full textOrientation of a Helical Nanofilament (B4) Liquid-Crystal Phase: Topographic Control of Confinement, Shear Flow, and Temperature Gradients
No full textOriented domains of the chiral/polar crystalline helical nanofilaments of the bent-core liquid crystal B4 phase are reported. A combination of topographic confinement of the bent-core molecule in micrometer-scale rectangular channels etched into a silicon surface with cooling from the isotropic melt in the presence of an air flow over the surface yields nanofilament orientation parallel to the flow
Probing the Morphology of Bulk Heterojunctions with Phthalocyanine and Naphthalocyanine Small Molecules: A Microwave and Solar Cell Device Study
No full textOrganic photovoltaics (OPVs) have the potential to provide clean, renewable energy. In this thesis work, solar devices were constructed by using an inverted architecture. Silicon naphthalocyanine (SiNc) and one of three phthalocyanine molecules (Pc1, Pc2, or Pc3) were separately added to the active layer of OPV solar cells in order to determine their impact on the performance and spectral response. Also, time-resolved microwave conductivity (TRMC) measurements were performed on thin films of P3HT:PC60BM with SiNc or one of three phthalocyanine molecules, neat P3HT with one of the small molecules, and neat PC60BM with a small molecule. The results from the TRMC experiments demonstrate that ternary blends showed characteristics of a three-phase morphology and it was possible to provide insight into the location of the molecules in the bulk heterojunction by analysis of the data. Therefore, TRMC has the potential to probe the morphology of different systems used for solar devices.</p
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