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`rx\J\§()LI3CULAI{ CRYSTALS AND LIQUII) CRYSTALS
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`SCIENCEANDTECIINOLOGY “ET-18-B93 I
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`Section A
`
`~ MOLECULAR CRYéTALS ~
`
`LIQUID CRYSTALS A
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`AND
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`comrzms
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`Page 1 of 17
`
`Tianma Exhibit 1033
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`Page 1 of 17
`
`Tianma Exhibit 1033
`
`

`
`MOLECULAR CRYSTALS AND LIQUID CRYSTALS
`SCIENCE AND TECHNOLOGY
`Section A
`MOLECULAR CRYSTALS AND LIQUID CRYSTALS
`Editor in Chief
`M. M. Labes, Department of Chemistry,
`Temple University, Philadelphia, Pennsylvania 19122 USA
`Manuscripts should be submitted to the following editors. See inside back cover for addresses. Notes
`for Contributors can be found at the back of the _)()U1'l'l'dl.
`
`M. Labes. (USA): G. Saitoi
`
`S. Chandrasekhar, (India); A. C. Griffin, (USA):
`Liquid Crystals: D. W. Bruce, (UK);
`(Japan); M. M. Labes, (USA); P. Pallf)“
`G. Heppke, (Germany); S. Kobayashi,
`Muhoray, (USA); F. Simoni, (Italy)
`Low-Dimensional Solids and Molecular Crystals: M.
`(Japan); F. Wudl, (USA)
`Book Reviews: D. J. Sandman, (USA)
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`M. A. ANisiMov (USA). R. BLINC (Slovenia), L. BLiN0v (Russia), A. BLUMSTEIN (USA), R. COMES (From-c).
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`(Japan), It. lNoi<uciii (Japan), J. D. LITSTER (USA), T.C. LUEENSKY (USA), R. B. MEYER (USA). C. M.
`Pmsos tcnm»). S.A. PIKIN (Ru.r.ria). N. PLAi1~:(Rimi'a). A. SAUPE (USA), M. scnmr tSwit:er1amD.E- F»
`SllF.KA (Ru.rsi'a), J. N. Slll3RW(}0D (Great Britain). A. SKoULios (France), I. TANAKA (Jcipan).G. WEGNER
`(Gerlmmy), J. wiLLiA.\is (USA), H. C, WOLF (Germany). H. YOKOYAMA (Japan), C. ZANNONI (Italy)-
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`

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`" Fry" 9"’ C’-V_" ~ V"1- 333v PP- M5‘
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`Reprints available directly from the publisher
`‘"“°°py‘”3 |"°"“'"‘d bl "“’"‘°‘ °"'l‘
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`(mulmr anti llreaclt .\x'l(‘llk‘\‘ l’rrl-inlet-i~ uupunl
`l'Ill||fll in Malaysia
`
`Effect of Chemical Structures
`of Polyimides on Photo—Alignment
`of Liquid Crystals
`
`M. NlSHlKAWAa' and J. L. wesrb
`
`“Tsukuba Research Laboratory, JSR Corporation, 25, Miyukigaoka, Tsukuba,
`lbaraki, 305-0841, Japan and “Liquid Crystal Institute, Kent State University,
`Kent, Ohio, 44242, USA
`
`(Received January 11, 1999; In final form Febmary 23, 1999)
`:
`
`Unidirectional liquid crystal (LC) alignment by a polarized UV exposure was examined using vari-
`ous polyimidcs (Pls) which consist of different tetracarboxylic dianhydrides and diamines. The dich-
`roic ratios and anchoring energies of the LC cells were measured as a function of polari/.cd UV
`exposure time. The results suggest that the unidirectional LC alignment for UV dosage is largely
`affected by the chemical structures of the Pls used. The LC alignment properties are sunnnarircd
`with respect to the UV absorption efficiencies, molecular conformations, and mechanisms ofdu:com-
`position of the PI films.
`
`Keywords: liquid crystal; polyimide; alignment; polarized UV exposure; unchurilltl Clwrtl)’
`
`1. INTRODUCTION
`
`Liquid crystal (LC) displays are widely used because of their low-power con-
`sumption, thin profile, and full—color capability. To fabricate LC displays, unidi-
`rectional LC alignment is typically produced using surface rubbing techniques
`[I]. However, this method has several problems. such as creation of contaminat-
`ing particles and production of electrostatic charges. which lower the production
`yield of LC displays. Therefore, alternative non-rub techniques to align LC are
`required.
`.
`.
`Langmuir—Blodgett
`films [2], stretched P0‘)/'“'~'r5 [3lv mi°’°‘3r""V°5 I41‘
`stamped polymers [5], and polarized ultraviolet light (UV) exposure of polymers
`* Correspondence Author.
`
`Page 3 of 17
`
`

`
`M. NISHIKAWA and J. L. WEST
`
`0
`
`FIGURE 1 Chemical structures of PIS containing various diamines
`
`[6], have been developed to produce unidirectional LC alignment. LC alignmeni
`produced using polarized UV exposure is the most promising non-rub technique.
`overcoming the problems mentioned above and greatly simplifying production
`of multi-domain LC displays [7].
`
`Photo-induced isomerization of azo compounds doped in polymers [6,8—l0l-
`cis-trans isomerization [II] or cross-linking [l2-I6] of poly(vinyl cinnamate)
`derivatives. and photo-decomposition of Pls [l7—23], have been shown to pm-
`ducc the alignment of LC by a polarized UV exposure. Much effort has been
`concentrated on the development of photoreactive Pls. which are more hcill
`resistant than azo compounds and poly(vinyl cinnamate) derivatives. One oflhc
`kc)’ d¢VCl0pment issues of photo-alignment materials is increasing their photo-
`sensitivity and anchoring energies as well as the quality of LC alignment. HOW-
`ever.
`the parameters of PI materials which affect
`the photosensitivity and
`anchoring energy have not been clarified yet. In this paper, we explore the effect
`of the PI chemical structures on the photo-alignment properties of LC.
`
`Page 4 of 17
`
`

`
`EFFECT ON PIS ON PHOTO-ALIGNMENT
`
`2. EXPERIMENTS
`
`2.1 Synthesis of Pls
`
`PI materials used in this experiment are summarized in Figures 1 and 2. PI films,
`except PI-8, were prepared by heat curing of precursor polyamic acids which
`were synthesized from the equal molar reaction between tetracarboxylic dianhy—
`drides and diamines. PI-8 is an organic-solvent-soluble polyimide synthesized
`from the reaction reported previously [24].
`
`2.2 Preparation of LC Cells
`
`LC cells were prepared to measure the dichroic ratios and azimuthal anchoring
`energies of the LCs aligned by polarized—UV—exposed PI films. PI films were
`deposited by first spin—coating dilute solutions of the respective polyamic acids
`or polyimide on ITO glass substrates and then cured at 250 °C for 1 hour to
`accomplish imidization [25]. The thickness of the PI film was controlled at
`50 nm.
`
`—~#vl~@@—
`
`/ \
`
`Pl-1
`
`Pl-8
`
`Pl-9
`
`JZEKTMII
`
`Pl-10
`
`o
`
`"‘©EI>ii:El
`
`Pl-11
`
`CF3
`
`FIGURE 2 Chemical stnrcturcs of Pls containing various tctracarboxylic dianhydrides
`
`Page 5 of 17
`
`

`
`I68
`
`M.NlSlllKAWA and.|.L. WEST
`
`The PI films were exposed with polarized UV incident normal to the surface.
`We used a 450 W-Xenon lamp (Oriel, model 6266) as a UV source, and a surface
`film polarizer (Oriel, model 27320) whose effective range is between 230 nm to
`770 nm. The intensity of UV after passing through the polarizer was monitored
`using a photometer, lntemational Light IL1700, and was about 1 mW/cmz at
`254 nm. LC cells were fabricated using two polarized—UV—exposed substrates
`with anti-parallel polarization axis. Dichroic LC, 0.5 % M-618 dichroic dye
`(Mitsuitoatsu, ?»max=550 nm) in n-pentylcyanobiphenyl (SCB, EM Industries)
`solution, and 5CB were filled into the cells in the isotropic state and slowly
`cooled to room temperature for measurement of the dichroic ratios and azimuthal
`anchoring energies of the LC cells, respectively.
`
`3Q
`
`U—
`
`J50-:
`O
`.9.on
`NI-
`.2OI-4
`.-C
`.2
`Q
`
`1
`
`100
`
`Polarized UV exposure time (min)
`FIGURE 3 R°l‘“i""*hiP bclwccn polarized UV exposure time and dichroic ratios of LC cells with W5
`shown In Figure l
`
`2.3 Measurement Methods
`
`The dichroic ratios of the LC cells were measured using one polarizer and :1
`UV-Vis spectrometer, Perkin Elmer Lambda 19 [22], The azimuthal anchoring
`
`Page 6 of 17
`
`

`
`EFFECT ON PIS ON PHOTO-ALIGNMENT
`
`I6‘)
`
`energies of the LC cells were measured utilizing the Neel wall method reported
`previously [26].
`
`1.0
`
`EU:...
`D-‘an
`)
`
`oQ
`
`is?.1:In
`cU!
`.1:
`
`< A
`
`bsorbanceofPIfilm
`
`0300 220 240 260 280 300 320 340 360 330 400
`Wavelength (nm)
`
`FIGURE 4 UV absorption spectra of PI films shown in Figure I
`
`The fluorescence spectra of PI films were measured in a front-face arrange-
`ment and the bandpasses were 1 nm for both the excitation and emission mono-
`ehrometers. The PI films were excited at their absorption maximum, and the
`
`Page 7 of 17
`
`

`
`l7()
`
`M. NISHIKAWA and .l. L. WEST
`
`emission from the PI films were monitored as a function of wavelength. The
`molecular conformations of the diamines and tetracarboxylic dianhydrides used
`in Pls were calculated by MOPAC Ver. 6 program with AMI parameters [27].
`
`PI—3
`
`PI-4
`
`mC
`
`.‘
`to1-.
`
`C ooC
`
`.‘
`to
`0U1
`03-:
`
`O 2L
`
`T-1
`
`300
`
`350
`
`400
`
`450
`
`500
`
`550
`
`600
`
`650
`
`700
`
`Wavelength (nm)
`FIGURE 5 Fluorescence spectra of Pl films shown in Figure I
`
`3. RESULTS AND DISCUSSION
`
`3. 1. Effect of Dlamlnes Used In Pls
`
`In this experiment, we used PI materials shown in Figure 1. Figure 3 shows the
`dichroic ratios of the LC cells as a function of the polarized UV exposure time.
`The dichroic ratios of the LC cells were defined as A C,/A am, where AW and
`AW” are the absorbances of the LC cells at 550 nm pergendipeular and parallel to
`the UV polarization, respectively. The dichroic ratios of the LC cells initially
`
`Page 8 of 17
`
`

`
`EFFECT ON PIS ON PHOTO-ALIGNMENT
`
`l7l
`
`increase logarithmically with UV dosage‘, and then approach a constant value of
`about 7.0, which is comparable with that of the LC cell with rubbed PI alignment
`films. The photosensitivity of LC alignment is largely affected by the diamine
`structures used in Pls.
`.
`
`104
`
`UI
`
`3
`
`in
`
`id3
`
`/5
`Fl
`
`E‘‘'H%
`
`isIn
`
`uGc
`
`uo
`
`n
`':Co
`.:
`
`‘r’.-c:
`Ta.4:0-‘
`:3
`
`.5.N
`<
`
`1
`
`10
`
`100
`
`Polarized UV exposure time (min)
`FIGURE 6 Relationship between UV exposure time and azimuthal anchoring energies of LC cells
`with Pls shown in Figure 1
`
`In our previous paper [28], we reported that the UV absorption efficiency of
`the PI film defined by the UV absorption and fluorescence of the PI film controls
`the photosensitivity of the LC alignment for UV dosage: i.e. higher UV absorp-
`tion or lower fluorescence of PI film results in higher photosensitivity of LC
`alignment for UV dosage. According to our previous work, we measured the UV
`absorption and fluorescent spectra of the Pl films containing different diamine
`moieties. Figures 4 and 5 show the UV absorption and fluorescence spectra of
`the Pl films as a function of wavelength, respectively. Measurement of fluores-
`
`cence spectra suggests that Pl-3. PI-4, and PI-6 show relatively strong fluores-
`
`Page 9 of 17
`
`

`
`M. NISHIKAWA and J. L. WEST
`
`U!
`
`3
`
`és
`
`1-: 3
`
`/\
`(‘I
`E\
`?\/
`>\
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`11)
`
`C0
`
`)G
`
`0
`I:
`‘C
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`N
`76J:«-
`
`3 EN <
`
`2
`
`3
`
`4
`
`5
`
`6
`
`Dichroic ratio of LC cell
`
`FIGURE 7 Relationship between dichroic ratios and azimuthal anchoring energies of LC cells with
`Pls shown in Figure l
`
`cencc due to the intra- or intennolecular charge-transfer (CT) [29] C0mP‘“°d
`with the other PI films competing with photodecomposition. This could be one
`reason why PI-3, H-4, and Pl-6 have relatively lower photosensitivity. On the
`other hand. the photosensitivity of LC alignment increases with the UV absorb-
`ances of the Pls except H-3, H-4, and PI-6 as shown in Figure 4.
`
`Figure 6 shows the relationship between polarized UV exposure time and lhc
`azimuthal anchoring energies of the LC cells. The azimuthal anchoring Cfl¢|'l:'l°5
`monotonically increased with UV exposure time, when the azimuthal anchorinfl
`°"°T8Y 55 above 5 X 10-5]/m2. the Neel wall in the LC cell disappears. And W119“
`the azimuthal anchoring energy is below I X l0'3 J/m2, we could not detect the
`Neel wall due to the disordered LC configuration. The azimuthal anchoring ener-
`gies gradually increase with polarized UV exposure time. Figure 7 shows lhc
`relationship between the dichroic ratios and the azimuthal anchoring energlcs "I
`
`Page 10 of 17
`
`

`
`EFFECT ON PlS ON PHOTO-ALIGNMENT
`
`PI-I
`V
`
`tr»
`
`*
`.»
`
`~«.~
`
`I
`'-
`
`r
`
`J
`
`~
`
`Pl~2
`
`,
`
`I
`
`‘V
`
`:
`
`,
`
`K,
`
`Pl-3
`,
`
`J
`
`H
`
`A
`
`.,
`
`A
`
`_
`
`p
`i
`
`T0pView
`4
`SideView HH-5
`
`‘J
`
`;
`
`P14
`
`7
`
`.
`
`(
`
`L
`
`H-7
`
`FIGURE 8 Molecular conformations of diamines
`
`the LC cells. The azimuthal anchoring energy and dichroic ratio appear to be log-
`arithmically related. The comparison of the anchoring energies of the LC cells
`with the same dichroic ratio suggests that the azimuthal anchoring energy is
`largely affected by the diamine structures in the Pls.
`
`To explain the effect of the diamines used in Pls in more detail. we calculated
`the molecular conformations of the diamines as shown in Figure 8. The compari-
`son of the molecular conformations suggests that the diamine with bulky molec-
`ular conformation tends to show relatively lower azimuthal anchoring energy
`than those with rigid molecular conformations.
`
`3. 2. Effect of Tetracarboxylic Dianhydrides Used In Pls
`
`In this experiment, we used PI materials shown in Figure 2. Figure 9 shows the
`dichroic ratios of the LC cells as a function of the polarized UV exposure time.
`The dichroic ratios of the LC cells initially increase logarithmically with UV. The
`photosensitivity of LC alignment is also considerably affected by the tetracar-
`boxylic dianhydrides used in Pls.
`
`Pl-I containing cyclobutane tetracarboxylie dianhydride moiety shows higher
`photoscnsitivity of LC alignment than those with other Pl films. The difference
`of the photosensitivity can be explained by the main mechanism of the decompo-
`
`Page 11 of 17
`
`

`
`M. NISHIKAWA and .l. L. WEST
`
`3o
`C)
`»—1
`90-:
`O
`.9i
`an3-1
`.2
`E.=
`.2
`D
`
`1
`
`100
`
`Polarized UV exposure time (min)
`FIGURE 9 Relationship between polarized UV exposure time and dichroic ratios of LC cells Will‘ P15
`shown in Figure 2
`
`sition of the Pls: cyelobutane ring cleavage [30,31] and imido ring cleavage [32]
`which requires higher UV dosage, respectively.
`We also measured the UV absorption and fluorescence spectra of PI films 60”‘
`taining different tetracarboxylic dianhydride moieties. Figure 10 shows the UV
`absorption spectra of PI films as a function of wavelength. Pl—ll shows relatively
`lower UV absorbance than that of PI-9. Furthermore, the measured fluorescencc
`of these Pl films were very small compared to those of other Pls shown I"
`Figure 5. In a series of experiments using Pls composed of cyclobutane tetracat
`boxylic dianhydride and various diamines [28], we obtained a clear relationship
`between the absorption efficiency of the PI films and the photosensitivity Oflhc
`LC alignment for UV dosage. However the data resulting from P1 materials con-
`taining different tetracarboxylic dianhydrides suggest that this experimental law
`cannot be applied to the Pl materials containing various tetracarboxylic dianhy-
`drides.
`
`Page 12 of 17
`
`

`
`EFFECT ON PIS ON PHOTO»/\LlGNMENT
`
`E14:F1
`0:
`2...
`
`0UUI
`
`:
`at
`.01-4
`0V)
`.0
`<
`
`200 220 240 260 280 300 320 340 360 380 400
`
`Wavelength (nm)
`
`FIGURE 10 UV absorption spectra of PI films shown in Figure 2
`
`Hoyle et al. compared the photodegradation of Pls (Pl-9 — ll) upon UV expo-
`sure [33]. and reported the tendency of PI material to be degradatcd as the fol-
`lowing:
`
`(Sensitive) Pl-ll > Pl-10 > Pl-9 (Less sensitive).
`
`Their results on the photodegradation of Pls coincide with the photosensitivity
`of LC alignment for UV dosage obtained in this‘ paper. Furthermore, they con-
`cluded that the CT characteristics in Pls largely affect the photodecomposition of
`PI chains [34]. The electron-withdrawing groups, such as ketonc in PI-I0 and tri-
`fluoromethyl in Pl-ll, affect the CT characteristics in Pls. and result in higher
`photosensitivity of LC alignment than that of Pl-9.
`Figure l I shows the relationship between polarized UV exposure time and the
`azimuthal anchoring energies of the LC cells. The azimuthal anchoring energies
`monotonically increased with UV exposure time. Figure l2 shows the relation-
`
`Page 13 of 17
`
`

`
`M. NISHIKAWA and J. L. WEST
`
`L
`
`E
`
`U!
`
`5
`
`r%
`(‘I
`E\
`‘-2»/
`>\
`ODx.
`Q)
`C(U
`D1)
`C
`':
`O
`.5(J
`CG}
`E-:{-5
`:3
`
`.§N
`<
`
`1
`
`10
`
`Polarized UV exposure time (min)
`
`FIGURE ll Relationship between UV exposure time and azimuthal anchoring energies of LC cells
`with Pls shown in Figure 2
`
`ship between the diehroic ratios and the azimuthal anchoring energies of the LC
`cells. The comparison of the anchoring energies of the LC cells with the sam¢
`dichroie ratio suggests that the azimuthal anchoring energy is also considerably
`affected by the tetracarboxylic dianhydride structures in Pls.
`
`The molecular conformations of the tetracarboxylie dianhydrides used in Pl‘
`were also calculated by the MOPAC Ver.6 program with AMI parameter.‘-
`Flgllre I3 shows the molecular conformations of the tetracarboxylic dianh)"
`drides used in Pls. It seems that the tetracarboxylic dianhydrides with bulk)’
`molecular conformations tend to show relatively weak azimuthal anchoring
`energy.
`l have reponed that the number of benzene in Pls affects the azimuthal
`anchoring energy due to the anisotropic van der Waals forces [35]. Beside lhcsc
`forces, the steric interaction between PI and LC is also a crucial parameter 10
`control the surface LC alignment.
`
`Page 14 of 17
`
`

`
`EFFECT ON PIS ON PHOTO-ALIGNMENT
`
`‘JI
`
`5
`
`in
`
`—O
`
`/\
`N
`EX
`'%\.l
`>.
`01)La
`cu
`::
`cu
`an
`.EI-
`o
`.c:U
`c:
`'6‘..c:14
`:3
`
`:c
`
`.§N
`<
`
`2
`
`3
`
`4
`
`5
`
`6
`
`Dichroic ratio of LC cell
`
`FIGURE 12 Relationship between dich roie ratios and azimuthal anchoring energies of LC cells wilh
`Pls shown in Figure 2
`
`4. CONCLUSION
`
`We reported the unidirectional LC alignment properties on P1 films with a polar-
`ized UV exposure. The photosensitivity of LC alignment and the anchoring ener-
`gies of the LC cells with various PI materials were measured as a function of
`polarized UV exposure time. The results suggest that the UV absorption efficien-
`cies. CT characteristics, molecular conformations and mechanisms of decompo-
`sition of the P1 films considerably affect the photoscnsitivity and anchoring
`energy for UV dosage. Further consideration of the azimuthal anchoring energy
`dependence, such as the relationship with UV dosage and dichroic ratio, is now
`underway. We will publish it elsewhere.
`
`Page 15 of 17
`
`

`
`M. NISHIKAWA and J. L. WEST
`
`Side View
`
`FIGURE I3 Molecular conformations of tetracarboxylic dianhydrides
`
`Ackna wledgemen ts
`We acknowledge Dr. L. C. Chien of Kent State University and Dr. Yu. Rcznikov
`of the Institute of Physics of the Ukrainian National Academy of Science for
`their useful discussion. We also thank Dr. N. Bessho and Dr. Y. Matsuki ofJSR
`Co. for their support in this research. Research was supported in part by the NSF
`Science and Technology Center ALCOM, DMR 89——20l47.
`
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