Photoconductivity in Discotic Liquid Crystals: A New Class of High-Mobility Materials

Haarer, D.; Adam, Dieter; Simmerer, J.; Closs, F.; Funhoff, D.; Häußling, Lukas; Siemensmeyer, K.; Ringsdorf, Helmut; Schuhmacher, Peter

doi:10.1080/10587259408038221

Cited by 12 publications

(5 citation statements)

References 23 publications

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“…Moreover, the orientation of columnar discotic phases can often be frozen into an ordered glassy state, 4 which is a most desirable feature from an application point of view. As a result, discotic LC systems are considered for use in devices such as organic light-emitting diodes (LEDs), 5,6 photoconducting layers for xerography, 7,8 and chemical sensors. 9,10 Columnar discotic LCs in which the disklike molecules spontaneously form one-dimensional molecular stacks that further assemble in a twodimensional lattice have been shown to exhibit high charge-carrier mobilities (of the order of 10 -3 -10 -2 cm 2 / V‚s) along the column direction.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, the orientation of columnar discotic phases can often be frozen into an ordered glassy state, which is a most desirable feature from an application point of view. As a result, discotic LC systems are considered for use in devices such as organic light-emitting diodes (LEDs), , photoconducting layers for xerography, , and chemical sensors. , Columnar discotic LCs in which the disklike molecules spontaneously form one-dimensional molecular stacks that further assemble in a two-dimensional lattice have been shown to exhibit high charge-carrier mobilities (of the order of 10 -3 −10 -2 cm 2 /V·s) along the column direction. , As a result, these materials may be particularly useful for applications in which an efficient unidirectional charge transport is desired; examples include the semiconducting layer in organic field-effect transistors , and the charge-transport or emitting layer in organic LEDs . Because of their particular photophysical characteristics, some columnar discotic LCs are also attractive for use in polymer-dispersed liquid crystals …”

Section: Introductionmentioning

confidence: 99%

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Uniaxial Orientation of Columnar Discotic Liquid Crystals

2002

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The present paper explores the possibility of orienting columnar discotic liquid-crystalline (LC) materials and causing a uniaxial "in-plane" orientation of the columns along the orientation direction. The discotic LCs employed were based on 2-hydroxy-3,6,7,10,11-penta-(1-butoxy)triphenylene, which was derivatized with 1-adamantenecarboxylic acid (Ada-PBT) and 10-undecenoic acid (ω-undecenoyl-PBT), respectively. As unequivocally shown by optical microscopy, uniaxial alignment of columnar Ada-PBT structures was readily achieved by spin-coating this material onto a poly(tetrafluoroethylene) orientation layer. Annealing of the films at temperatures at which the Ada-PBT was in its hexagonal plastic or hexagonal ordered mesophase slightly increased the degree of orientation. The optical absorption and photoluminescence spectra of oriented Ada-PBT films were significantly polarized, with absorption and emission dichroic ratios of 6.5 and 3, respectively. The optical anisotropy is unambiguously related to the uniaxial "in-plane" orientation of the cylindrical stacks of the LC molecules rather than an alignment of individual Ada-PBT molecules. Interestingly, this orientational behavior could not be mirrored when attempting to orient blend films of ultrahigh molecular weight polyethylene (UHMW-PE) and Ada-PBT or ω-undecenoyl-PBT by tensile deformation.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Uniaxial Orientation of Columnar Discotic Liquid Crystals

2002

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“…A variety of mesogens such as 2,3,6,7,10,11-hexaalkoxytriphenylenes, ,− phthalocyanines, ,− cyclotetraveratrylenes, sugars, , transition metal complexes, − hydrogen-bonded oligoheterocycles, − and diaza-crowns have been used to obtain discotic liquid crystalline materials. Some of these materials show high charge carrier mobilities; e.g., triphenylenes in the highly ordered hexagonal columnar mesophases (D h ) display charge carrier mobilities of 0.1 cm 2 V -1 s -1 , which are higher than any organic material except single crystal phases. ,− ,− This enhanced photoconductivity has been attributed to long-range ordering along the columns of the discotic hexagonal and helical phases.…”

Section: Introductionmentioning

confidence: 99%

“…Some of these materials show high charge carrier mobilities; e.g., triphenylenes in the highly ordered hexagonal columnar mesophases (D h ) display charge carrier mobilities of 0.1 cm 2 V -1 s -1 , which are higher than any organic material except single crystal phases. 2,[21][22][23][54][55][56] This enhanced photoconductivity has been attributed to long-range ordering along the columns of the discotic hexagonal and helical phases.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of Discotic Columnar Side-Chain Liquid Crystalline Polymers by Ring-Opening Metathesis Polymerization (ROMP)

et al. 1997

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Preparation of 1,2-didecyloxybenzene 4: 1-Bromodecane (100 g, 0.45 mol) was added dropwise under argon to a mixture of catechol (20 g, 0.182 mol) and potassium carbonate (82 g) in 200 mL dimethylformamide and the mixture was stirred under reflux for 24 hours. The mixture was filtered and the product precipitated as a white solid at OC. The crystalline solid was dried in vacuo to yield 49.5 g (70%). 1 H-NMR

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“…As a result, discotic mesogens are considered for use in electronic devices such as photoconducting layers [1,3], organic light-emitting diodes [4,5] and organic field effect transistors [6,7]. For device applications the orientation control of discotic liquid crystals is a crucial factor.…”

Section: Introductionmentioning

confidence: 99%

Surface controlled orientation of a novel star‐shaped discotic oligomesogen

Grafe

Jung²,

Sainova

et al. 2005

Liquid Crystals Today

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The alignment behaviour of a nematic-columnar phase forming discotic liquid crystal was explored on various substrates. The mesogen employed was a new star-shaped monodisperse oligomesogen characterized by three flat radial pentaalkynylbenzene moieties grafted to a central benzene linking unit via flexible alkyl spacers. It is shown that suitable polyimide orientation layers along with the mesomorphic properties give rise to a tilted alignment of the disc-shaped pentayne cores. The photoluminescence spectra of oriented films were lineary polarized upon isotropic excitation and unambigiously reveal that, beside the tilted alignment of the rigid cores, the molecular directors of the discotic building blocks preferentially are oriented along the rubbing direction of the orientation layer. The three-dimensional ordering is stable even at room temperature due to the glass forming properties of the applied discotic mesogen.

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Photoconductivity in Discotic Liquid Crystals: A New Class of High-Mobility Materials

Cited by 12 publications

References 23 publications

Uniaxial Orientation of Columnar Discotic Liquid Crystals

Uniaxial Orientation of Columnar Discotic Liquid Crystals

Synthesis of Discotic Columnar Side-Chain Liquid Crystalline Polymers by Ring-Opening Metathesis Polymerization (ROMP)

Surface controlled orientation of a novel star‐shaped discotic oligomesogen

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