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Rational synthesis of organic thin films with exceptional long-range structural integrity

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Science  05 Jun 2015:
Vol. 348, Issue 6239, pp. 1122-1126
DOI: 10.1126/science.aab1391

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Standing at order

Thin films of organic molecules on solid substrates tend to nucleate at many sites and grow multiple domains. However, one large uniform film would be much more desirable in device applications. Seiki et al. designed organic molecules that filled space in a hexagonal tiling; a propeller-like triptycene base adhered to crystalline surfaces and alkyl tails extended away from it. The authors could make well-ordered multilayer films up to centimeter length scales.

Science, this issue p. 1122

Abstract

Highly oriented, domain-boundary–free organic thin films could find use in various high-performance organic materials and devices. However, even with state-of-the-art supramolecular chemistry, it is difficult to construct organic thin films with structural integrity in a size regime beyond the micrometer length scale. We show that a space-filling design, relying on the two-dimensional (2D) nested hexagonal packing of a particular type of triptycene, enables the formation of large-area molecular films with long-range 2D structural integrity up to the centimeter length scale by vacuum evaporation, spin-coating, and cooling from the isotropic liquid of the triptycene. X-ray diffraction analysis and microscopic observations reveal that triptycene molecules form a completely oriented 2D (hexagonal triptycene array) + 1D (layer stacking) structure, which is key for the long-range propagation of structural order.

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