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Grazing Incidence X-ray Diffraction of a Photoaligned Nematic Semiconductor

Droge, Stefan, Al Khalifah, Manea S., O'Neill, Mary, Thomas, Huw Ellis, Simmonds, Henje Samuel, Macdonald, John Emyr, Aldred, Matthew P., Vlachos, Panos, Kitney, Stuart P., Lobbert, Andreas and Kelly, Stephen M. 2009. Grazing Incidence X-ray Diffraction of a Photoaligned Nematic Semiconductor. Journal of Physical Chemistry B 113 (1) , pp. 49-53. 10.1021/jp803379a

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Grazing incidence X-ray diffraction is used to find the thin film morphology of an extended molecule with an irregular alternating fluorene−thiophene structure, which is used to obtain linearly polarized electroluminescence and the photovoltaic effect. The material has a room temperature nematic glassy phase and is uniaxially aligned in the plane of the film using photoalignment techniques. Two distinct intermolecular separations of 0.45 and 1.5 nm are identified showing that the molecules are lamellar. The lamellae stack with only local order and the two short axes of the lamellae have no preferred orientation at the surface or bulk of the film. Neighboring molecules show a wide range of longitudinal displacements along the axis of the director, as expected for a nematic liquid crystal with no positional order. There is, however, a dominant feature corresponding to a longitudinal offset of 0.51 nm. Unlike some other fluorene-containing semiconductors where microphase separation of the side chains inhibits close packing of neighboring molecules, the lamellar structure and 0.45 intermolecular spacing found here allows π−π intermolecular interactions for efficient carrier transport. We obtain a room temperature hole mobility up to 3.4 × 10−3 cm2 V−1 s−1 using a time-of-flight technique.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Physics and Astronomy
Subjects: Q Science > QC Physics
Publisher: ASC Publications
ISSN: 1520-6106
Last Modified: 04 Jun 2017 03:21

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