A series of highly soluble maleimide-based polymers with photoreactive pendant group were synthesized and used as a gate dielectric insulator for organic thin film transistors. Photoalignment properties were characterized by UV-visible spectroscopy and the alignment of liquid crystals. Photopolymerization of polymer-coated organic thin film transistors with linearly polarized UV light induces anisotropy in field-effect mobility. The gate dielectric insulator based on the photoalignable maleimide shows higher field-effect mobility and on/off current ratio than those from a SiO 2 gate dielectric insulator with the values of 0.3 cm 2 V 21 s 21 and 10 4 , respectively. Our results demonstrate that the photo-induced anisotropy of alignment films to control the molecular order of semiconducting pentacene is a promising technology for improving the performance of organic thin film transistors.

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Pretilt angle measurable by using the conventional crystal rotation method is limited to about 0°–20° and 70°–90°. We propose a method by which we can measure the pretilt angle by using the crystal rotation method even if the pretilt angle is between 20° and 70°. In this method, the determination of a pretilt angle is achieved by finding the rotation angles where transmittances are maximum and minimum in the periodic transmittance characteristics obtained with the variation of rotation angle.

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