development of non-rubbing processes is essential. Therefore, photoalignment of LC
molecular films has received considerable attention. This is because photoalignment
process does not depend on electrostatic charge and dust in rubbing process. The
photoalignment method in which polyimide films are radiated with LPUV is one of
the most effective non-rubbing processes (Schadt et al. 1992). Ha et al. and Shitomi
et al. reported that the photoalignment characteristics of polyimide films, including
alicyclic and aromatic compounds, clearly depend on the wavelength of the exposure
photon (Shitomi et al. 1999; Ha and West 2002).
Gibbons et al. showed that curing the orientation of photosensitive layers with
polarized light may result in an “in-plane” orientation of the LCs on azo polymers
(Gibbons et al. 1991). In addition, Schadat et al. observed LC photoalignment on
coumarin-containing polymer layers (Schadt et al. 1992). However, these polymer
materials have low heat resistance, low optical transparency, and are dark brown or
yellowish brown.
Our preliminary experiments showed that 4,4-(hexafluoroisopropylidene)
diphthalic anhydride 2,3,5,6-tetramethyl-1,4-phenylene diamine (6FDA-TeMPD)
exhibits photoalignment characteristics (Sato et al. 2011a). This fluorine-containing
polyimide has high heat resistance (glass transition temperature, T g = 427
C), high
solubility in polar solvents, high optical transparency, and low refractive index
compared with other polymers.
This entry focuses on the photoalignment of LC molecules using fluorinecontaining polyimides.
Substituent Effect of Fluorine-Containing Polyimide
on Photoalignment of LC Molecules
6FDA-containing polyimides are expected to show high heat resistances, low
dielectric constants and refractive indices. The fluorine atom has high electronegativity, whereas the C-F bond has high binding energy and low polarizability. Thus,
fluorine-containing polyimides have high potential as materials for use in the LCD
industry. Most importantly, 6FDA is commercially available as a tetracarboxylic
dianhydride component, leading to its widespread use. In general, polyimides
containing 6FDA have excellent solubility in polar solvents and high optical transparency, along with a low refractive index. However, LC molecule photoalignment
on 6FDA-based polyimides has not been studied.
Hence, in the current study, we systematically investigated the substituent effect
of fluorine-containing polyimides with a 6FDA group on the photoalignment of LC
molecules and the effect of LPUV irradiation with a wavelength of 254 nm on the
chemical structure and the optical properties in infrared (FTIR) spectra, ultraviolet
(UV) absorption spectra, and molecular orbital (MO) calculations. In addition, the
LPUV photoreaction was also investigated.
The chemical structure of each product, as shown in Fig. 3, was confirmed by
FTIR spectroscopy and nuclear magnetic resonance analyses. The 6FDA-based
496
S. Sato et al.
molecular films has received considerable attention. This is because photoalignment
process does not depend on electrostatic charge and dust in rubbing process. The
photoalignment method in which polyimide films are radiated with LPUV is one of
the most effective non-rubbing processes (Schadt et al. 1992). Ha et al. and Shitomi
et al. reported that the photoalignment characteristics of polyimide films, including
alicyclic and aromatic compounds, clearly depend on the wavelength of the exposure
photon (Shitomi et al. 1999; Ha and West 2002).
Gibbons et al. showed that curing the orientation of photosensitive layers with
polarized light may result in an “in-plane” orientation of the LCs on azo polymers
(Gibbons et al. 1991). In addition, Schadat et al. observed LC photoalignment on
coumarin-containing polymer layers (Schadt et al. 1992). However, these polymer
materials have low heat resistance, low optical transparency, and are dark brown or
yellowish brown.
Our preliminary experiments showed that 4,4-(hexafluoroisopropylidene)
diphthalic anhydride 2,3,5,6-tetramethyl-1,4-phenylene diamine (6FDA-TeMPD)
exhibits photoalignment characteristics (Sato et al. 2011a). This fluorine-containing
polyimide has high heat resistance (glass transition temperature, T g = 427
C), high
solubility in polar solvents, high optical transparency, and low refractive index
compared with other polymers.
This entry focuses on the photoalignment of LC molecules using fluorinecontaining polyimides.
Substituent Effect of Fluorine-Containing Polyimide
on Photoalignment of LC Molecules
6FDA-containing polyimides are expected to show high heat resistances, low
dielectric constants and refractive indices. The fluorine atom has high electronegativity, whereas the C-F bond has high binding energy and low polarizability. Thus,
fluorine-containing polyimides have high potential as materials for use in the LCD
industry. Most importantly, 6FDA is commercially available as a tetracarboxylic
dianhydride component, leading to its widespread use. In general, polyimides
containing 6FDA have excellent solubility in polar solvents and high optical transparency, along with a low refractive index. However, LC molecule photoalignment
on 6FDA-based polyimides has not been studied.
Hence, in the current study, we systematically investigated the substituent effect
of fluorine-containing polyimides with a 6FDA group on the photoalignment of LC
molecules and the effect of LPUV irradiation with a wavelength of 254 nm on the
chemical structure and the optical properties in infrared (FTIR) spectra, ultraviolet
(UV) absorption spectra, and molecular orbital (MO) calculations. In addition, the
LPUV photoreaction was also investigated.
The chemical structure of each product, as shown in Fig. 3, was confirmed by
FTIR spectroscopy and nuclear magnetic resonance analyses. The 6FDA-based
496
S. Sato et al.