Photoalignment is one the important techniques to fabricate flat panel displays, birefringent functional films, and polarized optical diffraction devises. Thinner optical devises are attained when the optical film exhibits high birefringence. We investigated systematic studies on photoalignable liquid crystalline polymers (PLCPs), which achieve molecularly oriented structure for themselves, showing the bulk-photoalignment. This paper describes new PLCPs which reveal high photosensitivity, high photoalignability, and controllability of generated birefringence by means of in situ modification of the oriented mesogenic side groups. The initial generated birefringence of the PLCP films is 0.15, whereas the improved birefringence exceeds 0.4 is achieved via in situ modification of the oriented mesogenic side groups. Using PLCP films, polarization gratings are fabricated.
In this paper, we reported novel liquid-crystalline luminophore that switches its photoluminescent color by mechanically grinding. Mechanochromic luminescence (MCL) is expected for mechanical sensor, cellular imaging, detection of microenvironmental changes, and optical memory. In this work, we focused on liquid-crystalline MCL compounds on alignment layer. Controlling the molecular alignment of MCL compounds with photoalignment layer have potential to succeed in functional MCL film such as polarized micropatterned MCL and directional detection of mechanical stimuli. Herein, we prepared asymmetric rodlike MCL compounds containing cyano- and pyridyl molecular terminal and explored their photoluminescence behavior under mechanical stimulus. The cyano terminated compound showed a nematic phase and tuned its photoluminescent color from green to yellow upon grinding, while the pyridyl-terminated compounds that show no mesophase changed its photoluminescent color from blue to green and reverted to its initial color by heating above its melting point. The cyano-terminated MCL was aligned along the orientation direction of photoalignment layer and pyridyl-terminated MCL exhibited uniaxial alignment when it coated on photoaligned film containing carboxylic acid.
This paper demonstrates formation of surface relief (SR) gratings and crossed SR gratings with molecularly oriented
structure using photo-cross-linkable liquid crystalline copolymer films by means of holographic exposure of 325 nm He-
Cd laser beams combined with linearly polarized (LP) UV light. For the intensity holography using He-Cd laser, SR
gratings were formed after annealing the exposed films, where the molecular migration from the lower to the higherexposed
region occurred. The reorientational part and SR height were dependent on degree of the photoreaction. When
the exposure doses were low, molecular reorientation at the convex region was generated. In contrast, higher exposing
doses resulted in the molecular reorientation at the concave area. The resulting gratings showed polarization sensitivity
for diffraction efficiencies of the probe light beam according to the molecularly reorientation direction. Furthermore,
multi-holographic exposure yielded crossed SR gratings with reoriented structure according the polarization direction of
He-Cd laser beams, which exhibited multi-functional diffractions. Furthermore, when combining the multi-holographic
exposure and the unidirectional LPUV light exposure, crossed SR grating with multi-directionally oriented film structure
was generated., where the whole area was reoriented.
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