Bulk-mediated in-situ homogeneous photoalignment induced by reactive mesogen containing diphenylacetylene moiety

ABSTRACT

We designed and synthesised a reactive mesogen containing diphenylacetylene moiety in the mesogenic core and two polymerisable acrylate groups at both ends. By irradiating linearly polarised UV light on the conventional host LC mixture containing a small amount of the synthesised reactive mesogen in a sandwiched cell without an alignment layer, we demonstrated an in-situ photo-induced homogeneous alignment of liquid crystals without a pre-treated alignment layer, which was achieved by an irreversible polarisation-selective [2 + 2] photodimerization of diphenylacetylene moiety with linearly polarised UV irradiation at above the isotropic temperature of LC mixture. The resulting homogeneous alignment showed a superior initial dark state, negligible pretilt angle and excellent stabilities. Furthermore, the in-plane switching (IPS) LC cell prepared by this method exhibited a better dark state and electro-optic performance compared to that with conventional-rubbed polyimide alignment layer. The single photoirradiation process automatically resulted in a perfect alignment matching of optical axes between the top and bottom substrates in the LC cell, giving rise to an excellent dark state overcoming an intrinsic misalignment issue and complex fabrication process. The proposed in-situ alignment method is a promising candidate for cost-effective, green-manufacturing, and high-quality alignment technique in the manufacturing of high-resolution liquid crystal displays.

GRAPHICAL ABSTRACT

KEYWORDS:

• Reactive mesogen
• photoalignment
• homogeneous alignment
• photodimerization
• in-plane switching

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

The authors thank to the financial support from the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education [2018R1D1A1B07044250] and the Institute for Information & Communications Technology Promotion (IITP) under Grant funded by the Korea Government (MSIP) [R7520-16-0010]. The authors also would like to thank to the Polymer Materials Fusion Research Center of Jeonbuk National University. Pushan Wen also thanks to the financial support from the National Natural Science Foundation of China [Grant No. 21766040].