A convenient procedure to fabricate azobenzene-containing monolayers capable of performing the photoalignment of nematic liquid crystals (LCs) with pretilt angles has been elaborated. The photoactive monolayers were readily prepared by the surface-selective adsorption of p-butylazobenzene substituted with an ω-aminoalkyl residue to the outermost surface of a poly(acrylic acid) thin film. After the fabrication of an LC cell, the monolayers generated homeotropic LC orientation, which was transformed into homogeneous alignment with tilting angles by oblique irradiation with non- polarized UV light. The azimuthal direction of the photoinduced LC alignment was consistent with the propagation direction of the UV light, suggesting that the LC photoalignment results from direction-selective E to Z photoisomerization leading to re-orientation of the azobenzene chromophores. The photogenerated pretilt angles of LC alignment were significantly dependent on the dielectric anisotropy of LC and the surface density of the azobenzene in the monolayers.
ASJC Scopus subject areas
- Materials Chemistry