UV-Driven Switching of Chain Orientation and Liquid Crystal Alignment in Nanoscale Thin Films of a Novel Polyimide Bearing Stilbene Moieties in the Backbone

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• 作者：Suk Gyu Hahm ; Seung Woo Lee ; Taek Joon Lee ; Seon Ah Cho ; Boknam Chae ; Young Mee Jung ; Seung Bin Kim ; Moonhor Ree
• 刊名：Journal of Physical Chemistry B
• 出版年：2008
• 出版时间：April 24, 2008
• 年：2008
• 卷：112
• 期：16
• 页码：4900 - 4912
• 全文大小：808K
• 年卷期：v.112,no.16(April 24, 2008)
• ISSN：1520-5207

文摘

A novel photosensitive polyimide, poly(4,4'-stilbenylene 4,4'-oxidiphthalimide) (ODPA-Stilbene PSPI) wasnewly synthesized. The most surprising feature of this PSPI is that the PSPI films irradiated with linearpolarized ultraviolet light (LPUVL) can favorably induce a unidirectional alignment of liquid crystals (LCs)in contact with the film surface and further switch the director of the unidirectionally aligned LCs from aperpendicular direction to a parallel direction with respect to the polarization direction of LPUVL by simplycontrolling the exposure dose in the irradiation process. These LPUVL-irradiated films were found to providehigh anchoring energy to LCs, always giving very stable, homogeneous cells with unidirectionally alignedLCs regardless of the LC alignment directions. In the films, the PSPI polymer chains were found to undergofavorably unidirectional orientation via a specific orientation sequence of the polymer chain segments led bythe directionally selective trans-cis photoisomerization of the stilbene chromophore units in the backboneinduced by LPUVL exposure. Such unidirectionally oriented polymer chains of the films induce alignmentof the LCs along the orientation direction of the polymer chains via favorable anisotropic molecular interactionsbetween the oriented polymer chain segments and the LC molecules. In addition, the PSPI has an excellentfilm formation processibility; good quality PSPI thin films with a smooth surface are easily produced bysimple spin-coating of the soluble poly(amic acid) precursor and subsequent thermal imidization process. Insummary, this new PSPI is the promising LC alignment layer candidate with rubbing-free processing for theproduction of advanced LC display devices, including LC display televisions with large display areas.