宇佐美 清章

We have investigated the effect of alkyl-amine vapor treatment on pretilt angle generation by photo-alignment films of polyimide containing azobenzene in the backbone structure (Azo-PI). By performing alkyl-amine vapor treatment in preparing photo-alignment Azo-PI layers, the controllable range of the pretilt angle was extended at least up to 38° without appearance of threadlike disclination loops. We found that such a high pretilt angle was induced by the photo-alignment layers with a high inclination angle and narrow orientation distribution of the Azo-PI backbone structure in the out-of-plane direction.

<p>Photo-alignment efficiency of polyimides containing azobenzene in the backbone structure (Azo-PIs) is significantly enhanced by performing a simple alkylamine vapor treatment on the precursor (polyamic acid: Azo-PAA) films prior to photo-alignment. This is due to the efficient photo-induced rotation of Azo-PAA backbone structures in the amine-treated films, which are swollen by absorbing alkylamine molecules. In this study, we have examined the relationships between the amine vapor treatmen t time and the thickness of the amine-treated Azo-PAA film, and also between the amine vapor treatment time and the photo-induced in-plane anisotropy of the Azo-PAA and Azo-PI films.</p>

<p>By performing alkyl-amine vapor treatment in preparing photo-alignment layers of polyimides containing azobenzene in the backbone structure (Azo-PIs), the controllable range of the pretilt angle of liquid crystals can be extended at least to 38 without appearance of threadlike disclination loops. In this study, we have investigated the relationship between the average inclination angle of the Azo-PI backbo ne structure and the pretilt angle. We found that the pretilt angle increases with increas ing average inclination angle of the Azo-PI backbone structure.</p>

Recently, we succeeded in improving the controllable range of the pretilt angle of liquid crystal with defect-free alignment by using amine-vapor-treated photoalignment layers of polyimides containing azobenzene in the backbone structure (Azo-PI). The molecular orientation of the Azo-PI photoalignment layers with and without the amine vapor treatment was determined by measuring polarized infrared absorption spectra as a function of the angle of incidence. We found that the average inclination angle of the Azo-PI backbone structures in the amine-vapor-treated film was much higher than that in the untreated film.

ジアミノアゾベンゼンとピロメリット酸から合成されるポリアミック酸（Azo-PAA）の膜に斜めから無偏光紫外光を照射しその後熱イミド化することで、液晶にプレチルト角を誘起するポリイミド（Azo-PI）光配向膜が得られる。このAzo-PAAに側鎖を付与し、その導入量を制御することで、0度から90度の間の様々なプレチルト角を誘起することに成功したので、今回報告する。

フルオレンービチオフェンコポリマー（F8T2)は高分子電界効果トランジスタの活性層材料として注目されている。その分子配向を制御することにより電荷移動度を向上させることができることから、F8T2の配向制御は重要である。ポリイミド光配向膜を用いることにより、高配向F8T2膜を得ることができたので報告する。

光配向処理された骨格構造中にアゾベンゼンを含むポリイミド（Azo-PI）膜はその分子配向に大きな異方性を有する。この膜上の液晶単分子層の面内配向秩序度を偏光赤外吸収分光により測定した結果、Azo-PI膜により誘起される面内配向秩序度は0.4を超える大きな値であることがわかった。このAzo-PI膜を用いて液晶セルを作製したところ、非常に高い黒表示特性を実現することができた。

斜め無偏光（UP光）照射によって誘起されたアゾベンゼンを主鎖に含むポリイミド（Azo-PI）骨格構造の配向を調べた。UP光照射はAzo-PI の前駆体であるAzo-PAA膜に対して入射角45度で行った。Azo-PAA膜の厚さは16 nmであった。UP光照射量は882 J/cm²まで変化させた。熱イミド化した後、ポリイミド骨格構造の配向を偏光赤外吸収法によって決定した。その結果、無偏光紫外光の照射エネルギーの増加と共にポリイミド骨格構造が膜中の光電場最小の方向に配向していくことがわかった。

By using polarized infrared absorption spectroscopy, we have determined the average inclination angle of polyimide backbone structure in photo-aligned films. Polyimide used in this study contains azobenzene in the backbone structure. Photo-alignment treatment was performed for the corresponding polyamic acid film, using a light source of wavelength 340 〜 500 nm. The polyamic acid film (〜16 nm thick) was first irradiated at normal incidence with linearly polarized light (LP-light) of 156 J/cm^2, and then oblique angle irradiation of unpolarized light (UP-light) was performed in the plane of incidence perpendicular to the polarization direction of LP-light. We found that the average inclination angle of the polyimide backbone structure, measured from the surface plane, increases with the UP-light exposure.

We have investigated the pretilt angle of liquid crystal (LC) molecules induced by photoaligned films of polyimide containing azobenzene in the backbone structure. The polyimide films with different inclination of the backbone structure were prepared by performing photoalignment treatment for the corresponding polyamic acid films and then imidizing them thermally. The average inclination angle of polyimide backbone structure was determined by measuring the polarized infrared absorption spectra of the films as a function of the angle of incidence. The pretilt angle of LC molecules was determined by a crystal rotation method. A positive correlation (not linear relation) was found between the pretilt angle of LC molecules and the average inclination angle of the polyimide backbone structure.

We have investigated the molecular orientation of the polyimide film irradiated with p-polarized ultraviolet (UV) light at the incidence angle of 60°. The molecular orientation was determined from the incident angle dependence of the polarized infrared (IR) absorption spectra. The undecomposed polyimide molecules were, on average, inclined in the plane of incidence of the UV light. The inclination angle measured from the surface plane increased up to 〜10° with UV exposure.

We have determined the relation between the in-plane anisotropy of the molecular orientation of a liquid crystal (LC) monolayer and the underlying polyimide film exposed to linearly polarized ultraviolet light (LPUVL). To evaluate the anisotropy of the LC monolayer and the polyimide film surface, the sample orientation dependence of the polarized infrared absorption spectra was measured. The in-plane anisotropy of the LC monolayer was proportional to that of the polyimide film surface. This result suggests that the alignment of the LC molecules in contact with the LPUVL-exposed polyimide film is induced by a shortrange interaction between the polyimide and LC molecules.

By using polarized infrared absorption spectroscopy, we have investigated the molecular alignment of thin films of polyamic acid (PAA) containing azobenzene units in the backbone structure. The molecular alignment was induced by irradiation of linearly polarized ultraviolet light (LPUVL). We found that the alignment of the PAA molecule through repeated photo-isomerization reactions of the azobenzene unit occurred with a low efficiency. When the LPUVL-irradiated PAA film was thermally imidized, we observed significant enhancement in the molecular order of the film. We found that the enhancement of molecular order plays an important role in the realization of polyimide films with large in-plane anisotropy.

We have investigated the change in molecular orientational distribution caused by a washing treatment in UV irradiated polyimide (poly [4,4'-oxydiphenylene-l,2,3,4-cyclobutanetetracarboximide]) films. The polyimide films were exposed to linearly polarized UV light (LPUVL) at different energy densities. The molecular orientation of the LPUVL-exposed films was determined by measuring the polarized IR absorption spectra. In the UV exposure range below 1.5 J/cm^2, the film anisotropy slightly increases by the washing treatment and beyond this exposure it decreases. This result shows that the contribution of the polymer fragments with low molecular weights to the film anisotropy increases with the LPUVL exposure above 1.5 J/cm^2. Thus the film anisotropy becomes maximum at 1.5 J/cm^2 for the washed film, while 〜3 J/cm^2 for the unwashed film.

We have investigated the surface anisotropy of polyimide films induced by irradiation with linearly polarized ultraviolet light (LPUVL). The surface anisotropy was monitored by measuring the polarized infrared absorption spectra of 〜11 nm-thick films as a function of LPUVL exposure. The measurement was performed for) three kinds of polyimides: poly [4,4'-oxydiphenylene-pyromellitimide] (PMDA-ODA), poly [4,4'-oxydiphenylene-1,2,3,4-butanetetracarboximideI (BDA-ODA), and poly [4,4'-oxydiphenylene-1,2,3,4-cyclobutanetetracarboximide] (CBDA-ODA). We found that the LPUVL exposure dependence of the surface anisotropy is strongly influenced by the molecular structure of polyirnides.

We have measured the azimuthal anchoring strength of liquid crystal molecules in contact with poly[4,4'-oxydiphenylen-1,2,3,4-cyclobutanetetracarboxyimide] (CBDA-ODA) films. The measurement was performed for) a 10 nm-thick film exposed to linearly polarized ultraviolet light (LPUVL) of wavelength 〜250 nm at I J/cm^2 as well as for a rubbed film with the same film thickness. Tile infrared (IR) dichroic difference of the phenyl C-C stretching vibration of CBDA-ODA was almost the same for both films. However, the azimuthal anchoring strength for the LPUVI-exposed film was about 5 times smaller than that for the rubbed film. We believe that the small anchoring strength of the LPUVL-exposed film is due to the decrease of the molecular density and/or the decrease of the polyimide chain length that arise from the photo-induced decomposition. In our presentation. we will also report the relation between the IR dichroism of LPUVL-exposed films and the azimuthal anchoring strength.

We have measured the polarized infrared (IR) absorption spectra of poly[4,4'-oxydiphenylen-l,2,3,4- cyclobutanetetracarboxyimide] (CBDA-ODA) films irradiated with linearly polarized ultraviolet light (LPUVL) of wavelength 〜 250 nm. The measurement was carried out for a very thin film (10 nm thick) as a function of the LPUVL exposure. The dichroic difference, A_⊥- A_//, of the phenyl C-C stretching vibration of CBDA-ODA, which is polarized along the polyimide chain, has a maximum around 3 J/cm^2. Here A_//and A_⊥ are the absorbance for the IR light polarized parallel and perpendicular to the polarization direction of LPUVL, respectively. The dichroic difference per unit film thickness at 3 J/cm^2 was greater than that of a rubbed CBDA-ODA film with the same film thickness. Although the average IR absorbance, (A_⊥+ A_//)/2, decreases monotonically over the entire measurement range of LPUVL exposure, A_⊥ increases up to 1 J/cm^2. This result shows that the number of polyimide molecules oriented perpendicular to the polarization direction of LPUVL increases. We conclude that the photo-induced orientation contributes to the large surface anisotropy of LPUVL-exposed CBDA-ODA films in addition to the anisotropic photo-induced decomposition.