Guided Assembly of Linear Diacetylenic Acid Molecules by Solution Shearing: An Odd–Even Effect in Film Morphology and Charge Transport Properties AITranslate

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DOI：https://doi.org/10.1021/acsapm.3c00418

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Guided molecular assemblies of a series of linear diacetylenic acids (C12-C≡C-C≡C-Cn-COOH, with n = 7–11) were prepared on silicon substrates by a solution-shearing method. Upon UV irradiation, well-aligned poly(ene-yne) conjugate backbones along the shearing direction were successfully obtained for all acids used. However, different morphologies were observed, depending on the chain length of the spacer group Cn between the diacetylene unit and the carboxyl group. An odd–even effect in the morphology was observed in that smooth, continuous yet striped morphology was observed with Cn of odd carbon number (n = 7, 9, and 11), whereas with Cn of even carbon number (n = 8 and 10), a patchy and noncontinuous morphology was observed. This is in distinct contrast with the odd–even effect for thermally evaporated films previously observed: a ring-type morphology for acids with Cn of odd carbon number and a dendrite-like morphology for acids with Cn of even carbon number. The structures of the films before and after polymerization were characterized by tools including polarized optical microscopy, UV spectroscopy, and grazing incidence X-ray diffraction. The “odd–even effect” in morphology was also discovered in other characteristics and properties such as film orderliness, roughness, and etc. as a result of different crystal packing motifs of C12-C≡C-C≡C-Cn-COOH in the sheared films. Thin-film transistors based on these films were fabricated, with the average mobility ranging between 0.37 and 2.51 cm2/Vs, and the highest mobility of 3.32 cm2/Vs was achieved for the device based on the acid with n = 9.