Alignment Control of a Columnar Liquid Crystal for a Uniformly Homeotropic Domain Using Circularly Polarized Infrared Irradiation

Monobe, Hirosato; Awazu, Kunio; Shimizu, Yo

doi:10.1002/adma.200501762

Cited by 46 publications

(33 citation statements)

References 20 publications

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“…Polarized infrared irradiation [51] or specific molecular interface interactions [52] can assist the alignment process. The perfection of the orientation of the molecules in the monodomains is essential for TOF measurements and the sign of the charge carriers.…”

Section: à4mentioning

confidence: 99%

Liquid Crystalline Ordering and Charge Transport in Semiconducting Materials

Pisula¹,

Zorn²,

Chang³

et al. 2009

Macromol. Rapid Commun.

374

276

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Organic semiconducting materials offer the advantage of solution processability into flexible films. In most cases, their drawback is based on their low charge carrier mobility, which is directly related to the packing of the molecules both on local (amorphous versus crystalline) and on macroscopic (grain boundaries) length scales. Liquid crystalline ordering offers the possibility of circumventing this problem. An advanced concept comprises: i) the application of materials with different liquid crystalline phases, ii) the orientation of a low viscosity high temperature phase, and, iii) the transfer of the macroscopic orientation during cooling to a highly ordered (at best, crystalline-like) phase at room temperature. At the same time, the desired orientation for the application (OLED or field-effect transistor) can be obtained. This review presents the use of molecules with discotic, calamitic and sanidic phases and discusses the sensitivity of the phases with regard to defects depending on the dimensionality of the ordered structure (columns: 1D, smectic layers and sanidic phases: 2D). It presents ways to systematically improve charge carrier mobility by proper variation of the electronic and steric (packing) structure of the constituting molecules and to reach charge carrier mobilities that are close to and comparable to amorphous silicon, with values of 0.1 to 0.7 cm(2) · V(-1) · s(-1) . In this context, the significance of cross-linking to stabilize the orientation and liquid crystalline behavior of inorganic/organic hybrids is also discussed.

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Section: à4mentioning

confidence: 99%

Liquid Crystalline Ordering and Charge Transport in Semiconducting Materials

Pisula¹,

Zorn²,

Chang³

et al. 2009

Macromol. Rapid Commun.

374

276

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“…These techniques include zone casting, [6c] frictiontransferred PTFE templates, [1c,7] Langmuir-Blodgett films, [8] stationary nozzles onto a moving substrate, [9] and more recently magnetic field-induced, [10] field-force alignment, [11] and circularly polarized infrared irradiation. [12] However, the lateral resolution of the uniaxial alignments in these studies is limited to a few nanometers and the growth of the columns is induced either by a field (magnetic or electrical), a mechanical constraint, or a dewetting process. Finally, most of the above cited techniques always end up with monolayers and do not permit to control the formation of multilayered columnar stacks.…”

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confidence: 99%

Hierarchical Self‐Assembly of Edge‐On Nanocolumnar Superstructures of Large Disc‐Like Molecules

et al. 2008

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Large disk-like aromatic molecules bearing long peripheral aliphatic side-chains can form columnar liquid crystals, that is large oriented domains with good one-dimensional charge transport properties. [1] In most cases, these planar molecules adopt a natural face-on arrangement on the substrate and grow as vertical columnar stacks; they can find applications in sandwich devices such as solar cells and optical displays.[2]Besides, a number of techniques have recently been developed to grow columnar stacks lying parallel to the substrate surface, that is, with molecules standing edge-on, an orientation that could be useful for devices having coplanar electrodes such as field-effect transistors. For example, porphyrins, [3] phthalocyanines, [4] triphenylenes, [5] and hexa-peri-hexabenzocoronenes (HBCs) [6] can form uniaxial alignments lying horizontal on different types of substrates by using appropriate techniques. These techniques include zone casting, [6c] frictiontransferred PTFE templates, [1c,7] Langmuir-Blodgett films, [8] stationary nozzles onto a moving substrate, [9] and more recently magnetic field-induced, [10] field-force alignment, [11] and circularly polarized infrared irradiation. [12] However, the lateral resolution of the uniaxial alignments in these studies is limited to a few nanometers and the growth of the columns is induced either by a field (magnetic or electrical), a mechanical constraint, or a dewetting process. Finally, most of the above cited techniques always end up with monolayers and do not permit to control the formation of multilayered columnar stacks. We here show by means of scanning tunneling microscopy (STM), a versatile technique for imaging adlayers at the (sub)molecular scale, [13] at the n-tetradecane/graphite interface that hexakis-(n-dodecyl)-peri-hexabenzocoronene (HBC-C 12 ) [14] spontaneously forms uniaxial columnar stacks on graphite. These nanocolumns are aligned horizontally on the substrate, with individual molecules in edge-on orientation, and are adsorbed on an intermediate face-on HBC-C 12 monolayer into {HOPG/face-on/edge-on} self-organized systems. Visualization of the nanocolumnar stacks depends on the voltage applied to the STM tip due to tunneling transparency. We explain the formation of these columnar superstructures by the strong tendency of HBC-C 12 to aggregate in p-stacks or mesophases due to its liquid crystalline properties.[15] Finally, three face-on and edge-on layers can be superimposed on top of each other to form complex supramolecular 3D architectures {HOPG/face-on/edge-on/edge-on} and {HOPG/face-on/ edge-on/face-on}.In the tip voltage range V t ¼ 0.2-0.6 V, only a HBC-C 12 face-on monolayer is visible by STM at the n-tetradecane/ graphite interface (Figure 1). Two rhombic phases coexist COMMUNICATION Figure 1. STM images of the two face-on rhombic phases of HBC-C 12 directly adsorbed on the basal plane of HOPG at the n-tetradecane/ graphite interface: (a) Phase 1 (7 nm Â7 nm; I t ¼ 20 pA; V t ¼ 0.450 V) and (c) Phase 2 (7.5 Â 7.5 nm; I t...

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“…Recently, it was observed that homeotropic alignment in films confined between two surfaces could be facilitated by irradiating the sample with circularly polarized infrared light at the wavelength corresponding to vibration of a chosen chemical bond of the LC molecule. [14] Another possible way to create homeotropic alignment consists in the use of a template (e.g., nanoporous alumina) attached to the first electrode, which could guide the alignment of the LC. [15] The deposition of the second electrode will be preceded in this case by removal of the template.…”

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Homeotropic Alignment of Columnar Liquid Crystals in Open Films by Means of Surface Nanopatterning

et al. 2007

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Columnar liquid crystals (LCs) are reported to align spontaneously homeotropically—that is, orthogonally to the surface (see figure and inside cover)—on a glass surface covered with a layer of poly(tetrafluoroethylene) transferred by friction (rubbing). This strategy for producing macroscopic monodomains of homeotropically aligned LCs may find important applications in the fabrication of LC‐based organic solar cells.

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Alignment Control of a Columnar Liquid Crystal for a Uniformly Homeotropic Domain Using Circularly Polarized Infrared Irradiation

Cited by 46 publications

References 20 publications

Liquid Crystalline Ordering and Charge Transport in Semiconducting Materials

Liquid Crystalline Ordering and Charge Transport in Semiconducting Materials

Hierarchical Self‐Assembly of Edge‐On Nanocolumnar Superstructures of Large Disc‐Like Molecules

Homeotropic Alignment of Columnar Liquid Crystals in Open Films by Means of Surface Nanopatterning

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