Poly(esterimide) bearing azobenzene units as photoaligning layer for liquid crystals

• Azofunctionalized polymer was used as photoalignment layer for liquid crystal.
• Poly(esterimide) with side azobenzene derivative substituted with fluorine was applied.
• This polymer exhibited high level of photoinduced birefringence and low its relaxation in the dark.
• A stronger anchoring of the LC compare to rubbed was obtained.

The custom synthesized azobenzene side-chain poly(esterimide) was used as an aligning material for nematic liquid crystal molecules. The anisotropy of the poly(esterimide) layer was generated by a linearly polarized UV light, as a consequence of multiple trans–cis–trans isomerization cycles. The photoalignment effect was studied by assembling a twisted nematic cell with a proper liquid crystal mixture and geometry to fulfill Mauguin’s limit. The polarizing microscope pictures of the fabricated cells confirmed the twisted arrangement of liquid crystal molecules. The results of electro-optic measurements indicated a stronger anchoring of the liquid crystal molecules by photoaligned poly(esterimide) than that obtained in the case of a rubbed polyimide.