Polydiacetylene Microcrystals for Third-Order Nonlinear Optics

Chapter 13

Downloaded by UNIV MASSACHUSETTS AMHERST on October 7, 2012 | http://pubs.acs.org Publication Date: September 1, 1997 | doi: 10.1021/bk-1997-0672.ch013

Polydiacetylene Microcrystals for Third-Order Nonlinear Optics Hachiro Nakanishi and Hitoshi Kasai Institute for Chemical Reaction Science, Tohoku University, Sendai 980-77, Japan

Microcrystals of some diacetylenes, prepared by the reprecipitation method, have been studied as dispersions in liquid media. Interesting behavior has been observed in the solid-state polymerization of diacetylene monomers and with the optical properties of polydiacetylene (PDA) microcrystals. First, the polymerization perfectly proceeded from one end to the other end of the diacetylene microcrystals. Next, the excitonic absorption peak position was found to shift to higher energy side with decreasing size of the PDA microcrystals. The size effect was observed even for crystals as large as 100 nm or more in contrast to conventional quantum effect of inorganic semiconductors where size effect is observed only for microcrystals of less than about 10 nm size. In addition, since the microcrystal dispersions in water have low optical loss, the optical Kerr shutter response of PDA microcrystals could be measured, and the non-resonant χ value was estimated to be on the order of 10 to 10 esu in very low concentrations (ca.10 M). (3)

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Organic compounds with delocalized π-electron systems, e.g., π-conjugated polymers, are considered to be candidates for third-order nonlinear optical materials. Among them, polydiacetylenes (PDAs) are an important class of conjugated polymers that has attracted investigators from many different fields (1,2). PDAs, which can be obtained as single crystals by topochemical solid-state polymerization (3), have been extensively studied since 1976 (4). PDAs show large third-order nonlinear optical susceptibilities (5) and ultrafast optical © 1997 American Chemical Society

In Photonic and Optoelectronic Polymers; Jenekhe, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.

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responses; therefore, they have been considered to be very promising materials for future photonic technologies (6-8). However, it is difficult to prepare large PDA crystals with good optical quality. This is a serious problem as far as the application of PDA bulk crystals for photonic technologies are concerned. On the other hand, organic materials can readily make glasses or liquids with high optical quality. Using liquid media, the optical Kerr shutter (OKS) is considered to be one of the most promising devices for ultrafast all-optical signal processing based on third-order nonlinearity (9-11). OKS materials are required to satisfy the following factors: (A) high optical transparency, (B) large susceptibilities, and (C) ultrafast response. OKS experiments with organic materials have so far been mainly performed with solutions. Recently, many researchers have studied fine particles or microcrystals to clarify the intermediate state between bulk crystals and isolated atoms and molecules (12-16). From these studies in the field of nonlinear optics, Hanamura predicted excitonic and surface-state enhancements of third-order optical nonlinearity in microcrystals because of quantum confinement effects, which is one of several size effects theoretically established by Ekimov et al. and Brus (1719). Following these theories, enhancements of χ ® have been reported in semiconductor-microcrystallite-doped glasses and polymers (20,21). Organic microcrystals, however, have attracted very little attention so far (22,23) owing to the difficulties of preparing them. Since 1992, we have succeeded in obtaining some organic microcrystals by the conventional reprecipitation method (24). For PDA microcrystals, we have been able to find interesting optical properties as well as characteristic polymerization behavior (25,26). Moreover, among the many compounds investigated, some of the microcrystal-dispersed liquids were found to show little light scattering because the crystal sizes were smaller than the relevant wavelengths. They are stable without cohesion in liquids or matrices for more than half a year in spite of high concentration. Therefore, if these microcrystal dispersions are applied for OKS, it will be possible to achieve low optical-loss and large χ ® materials. Many promising crystalline materials could thereby be used for OKS. In this article, we will describe in detail the preparation of diacetylene (DA) microcrystals and their solid-state polymerization behavior and optical properties as a function of crystal size. In addition, we also report OKS response of organic microcrystal dispersions. EXPERIMENTAL SECTION Preparation of DA Microcrystals. The DA derivatives used in this work were 5,7-dodecadiynylene bis(JV-(butoxycarbonylmethyl)carbamate) (4BCMU), 10,12-heptacosadiynoic acid (14-8ADA), and l,6-di(^-carbazolyl)-


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PDA Microcrystals for Nonlinear Optics

185

2,4-hexadiyne (DCHD), as shown in Figure 1. These compounds are known to have large third-order nonlinear optical properties(4). Their microcrystal dispersions in water were prepared by the simple and easy reprecipitation method developed and established by our group(24). For example, in the case of 14-8ADA, 250 μΐ of 1.0 χ ΙΟ" M acetone solution was injected into 10 ml of water with 20 mg of poly(vinly alcohol) at room temperature. PDA microcrystals were obtained by UV irradiation of the microcrystal dispersions of the corresponding monomers. Downloaded by UNIV MASSACHUSETTS AMHERST on October 7, 2012 | http://pubs.acs.org Publication Date: September 1, 1997 | doi: 10.1021/bk-1997-0672.ch013

2

Characterization of PDA Microcrystals. Scanning electron microscope (SEM; Hitachi S-900) and dynamic light scattering (DLS; Otsuka electronics DLS-7000) were used to evaluate the size of microcrystals. The molecular weight of poly(4BCMU) microcrystals was estimated by gel permeation chromatography (GPC; Shimadzu LC-8A, Shodex GPC K-80M). Monodispersed polystyrene (Toso) was used as a standard sample. Solid-state polymerization of DA microcrystals was monitored by observing the changes in UV absorption spectrum and by determining the conversion using Differential Scanning Calorimetry (DSC; Rigaku 8240B). Experimental System for O K S . The optical system for OKS measurements is shown in Figure 2. All the dispersions were put in a 10-mm quartz cell between a polarizer and an analyzer in cross Nicol configurations. OKS experiment was performed using Nd:YAG laser at 1064 nm with 6 ns pulse width, 6.3 mW power and 10 Hz repetition as a gate beam, and a laser diode at 813 nm with 100 ns pulse width as a probe beam. A Photomultiplier tube with a 2 ns response was employed as a detector. The refractive index (n) and χ ® value of carbon disulfide used as a reference are 1.62 and 3.7 x 10" esu, respectively (25). Details of the experimental set-up are described in previous papers (26). a

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RESULTS AND DISCUSSION Solid-State Polymerization of 14-8ADA Microcrystals. Solidstate polymerization is naturally influenced by the lattice mismatch between monomer and polymer crystals as well as the lattice rigidity. Tieke et al. (27) reported that strain in the bulk crystal is relaxed by a phase transition to some extent, in which the continuous phase is transformed from monomer rich region to polymer rich one in the course of the polymerization. Such a phase transition is considered to occur easily in a microcrystal, compared with a bulk crystal, because of loosening of the crystal lattice with decreasing crystal size. This must especially be the case with 14-8ADA which has a rather weak crystalline lattice due to its long alkyl chains. DSC measurements of DA crystals show that the area of the endothermic peak decreases upon UV or γ-ray irradiation due to the formation of




R'

Monomer 14-8ADA : R = - { C H ^ C H a , R'= - { C H ^ C O z H

DCHD : R = R = - C H Ν 2

4 BCMU :

R = R'

= -{CH^OCONHCHzCOO-nBu

Figure 1. Diacetyrene œmpounds used for the preparation of microcrystals.

Pump beam Probe beam Polarizer

Analyzer

Pump beam : wave length 1064 nm duration 6 ns power 6.3 mW cycle 10 Hz Probe beam : wave length 813 nm duration 100 ns cycle 10 Hz Pass length : 10 mm

Figure 2. Experimental set-up for the measurements of Kerr effect.



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polydiacetylene(2#). The amount of residual monomer in a crystal could be estimated from the heat of fusion. The final conversion of 14-8ADA thus determined is summarized in Table I. The results with either UV or γ-ray irradiation were almost the same. Interestingly, the final polymer conversions with microcrystals were larger than with bulk crystals. It turns out that the loose crystalline lattice of microcrystals allows the strain to be easily relaxed. In microcrystals of several nanometer size, however, the conversion was 75% which is lower than that of submicrometer crystals, in spite of the smaller crystal size. This is due to excessive enhancement of thermal vibrations of the crystal lattice in this type of long-alkyl-substituted diacetylene. This is considered to be a kind of dynamic defect in the crystal lattice that disturbs the solid-state polymerization. Such enhanced thermal vibration is also estimated to be one of the main reasons for the size-dependent shift of absorption peaks as mentioned later. Table I. The Final Polymer Conversion of 14-8ADA Crystals with Different Sizes Methods for polymerization

Bulk crystals

Microcrystals (Sub μπι)

Microcrystals (A few nm)

UV irradiation

35%

97%

75%

X-ray irradiation

49%

-100%

76%

Degree of Polymerization of Poly(4BCMU) Microcrystals. Another point that we want to emphasize is the possibility of synthesizing PDAs with narrow molecular weight distribution; this may lead to sharper absorption due to regular and uniform electronic states in the PDA backbones. The principle idea to achieve this is as follows: when the polymerization proceeds in microcrystals, whose size is smaller than the propagation length, every single polymer chain must reach from one end to the other of the microcrystal. Upper views in Figure 3 represent microcrystals with different sizes and shapes. Horizontal lines in these figures are for conjugated backbones of PDA and outlines show the edges of the microcrystals. Lower views in Figure 3 indicate molecular weight distributions monitored by GPC. The horizontal axes are retention time; longer retention time corresponds to lower molecular weight. Considering that solid-state polymerization is stopped by defects, polymerization in microcrystals is expected to proceed continuously until the polymerization reaches both edges of the microcrystals as shown in (a) to (c) because the number of defects should be reduced owing to the small number of molecules in the microcrystals. If we obtain size-controlled microcrystals with the rectangular shapes (a) and (b), molecular weight distribution becomes more mono-dispersed and the molecular weight of the polymer depends on the size of the microcrystals. Even in the case of (c), the molecular weight of the polymer must be roughly controlled by crystal size though its distribution is broader than (a) and (b).



PHOTONIC AND OPTOELECTRONIC POLYMERS

3

i l .

.A

,A

Q P C retention time

a

b

c

Figure 3. Schematic diagrams on the polymerization of diacetylene microcrystals. In the upper figure, size of microcrystals and polymer backbones are indicated by thick outlines and thin lines, respectively. The lower figures show GPC data expected for the polymers obtained from each upper microcrystal.



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189

As a preliminary experiment to prove this hypothesis, microcrystal fabrication of poly(4BCMU) was investigated. Since this polymer is soluble in chloroform, molecular weight distribution was evaluated using GPC. Two kinds of poly(4BCMU) microcrystals with different crystal sizes (300 nm and 1 μτο) were obtained by changing water temperature in the reprecipitation method, as shown in Figure 4. It was expected that high and low molecular weight poly(4BCMU) would be obtained from the sample with crystals of large (sample A) and small (sample B) size, respectively. Indeed, the polymer prepared from larger microcrystals showed higher molecular weight as summarized in Table II (28,29) Surprisingly, these values coincide well with those calculated from their crystal sizes on the assumption that the repeat length of poly(4BCMU) is ca. 0.5 nm. Thus, solid-state polymerization of this PDA monomer is estimated to proceed from one end to the other of the microcrystals. The molecular weight distribution of poly(4BCMU) bulk crystals was much broader than that of microcrystals, and the molecular weight was lower, indicating that polymer lengths in bulk crystals are regulated by the distance between randomly distributed defects. Though the size control of the microcrystals was not exact, the present results clearly demonstrate the possibility of synthesis of monodisperse polymers using topochemical polymerization of microcrystals. In order to decrease Mw/Mn value we are making efforts to prepare the microcrystals with monodispersed size and polymerize them from one end to the other. Table Π. Molecular Weight of Poly (4BCMU) Microcrystals Size of microcrystals (μτη)

a

Molecule weight Mw Mn

Mw/Mn

6

5.2 χ 10

5

3.1

5

1.6 χ 10

5

3.4

0.5 -1.5

1.6 χ 10

0.2-0.4

5.5 χ 10

Determined by GPC using polystylene as a standard. Optical Properties of PDA Microcrystals of Different Sizes. The effect of average molecular weight on the functions of PDA microcrystals is expected to be important from the point of view that the electronic and nonlinear optical properties of quantum-wire and quantum-dot structures differ significantly from those of bulk crystals. An enhancement of several orders of magnitude in thirdorder optical nonlinearities has been predicted in the case of quantized microcrystallites. To examine such size effects, different sizes of DCHD microcrystals were




Figure 4. SEM photographs of poly(4BCMU) microcrystals with average size of (a) 1 μ m and (b) 300 nm.


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prepared using the reprecipitation method (28,30,33). DCHD was selected because of its rigid and ideal packing and the peak position of the excitonic absorption of the resulting polymers for each microcrystal size never moved in the course of polymerization. Therefore, the size effect could be unambiguously examined. There are many factors which are believed to play a role in controlling the size of microcrystals. One of the most effective factors is the water temperature. For example, in the case of DCHD, when 250 μΐ of 7.0 χ ΙΟ" M acetone solution was injected into 10 ml of water at 343, 298, and 273 K, the crystal size was 70, 100, and 150 nm, respectively (Figure 5). The shape of the DCHD microcrystals was found to be intact by SEM observation before and after solid-state polymerization. Figure 6 shows the optical absorption spectra of poly(DCHD) microcrystals in water with different crystal sizes. The excitonic absorption peak positions of poly(DCHD) microcrystals of 70, 100 and 150 nm in size were 652 nm, 646 nm, and 640 nm, respectively. That is, the absorption energy of exciton was found to shift to the high energy side with decreasing crystal size.


3

Reasons for Size Effects in Organic Microcrystals. Table III summarizes the size-dependence of optical absorption properties among organic superlattice, PDA, perylene, and semiconductor microcrystals (20,31-35). Size effects in organic superlattice as well as semiconductor microcrystals appear upon reducing the size to less than 10 nm, and the cause of these effects has been explained in terms of quantum confinement. However, interestingly, in the case of organic microcrystals such as PDA and perylene, the high energy shifts in the excitonic absorption were observed, even though the crystal size was much larger than about 100 nm. The cause for this peculiar phenomenon is not clear. Two factors are presumed to be the cause of the size effect in organic microcrystals. One is the change of lattice state. Because the lattice would soften by microcrystallization, the coulombic interaction energies between molecules get smaller. As a result, optical absorption properties of molecules would change in microcrystals. The other is the electric field effect of the surrounding media with varying dielectric constants. This is currently under investigation. In the near future, this size effect of organic microcrystals might be explained by a new quantum confinement model. At present, however, it is important to prepare organic microcrystals with sizes less than 10 nm in the free-standing state, and to clarify their optical properties. OKS Measurements of PDA Microcrystals. In OKS experiments, the probe beam through two polarizers in a cross Nicol state was detected because of the induced birefringence resulting from high intensity gate light incident upon the sample. The χ ® value was evaluated by probe transmittance (T). Equations (1) and (2) show the relationship between Τ and the nonlinear optical coefficient (n^ as follow;




Figure 5. SEM photographs of poly(DCHD) microcrystals with average size of (a) 70 nm (b) 100 nm and (c) 150 nm.



NAKANISHI & KASAI


Figure 5. Continued.

λ/nm

Figure 6. Relationship between visible absorption spectra of poly(DCHD) microcrystals dispersed in water and their crystal size.


194

PHOTONIC AND OPTOELECTRONIC POLYMERS

Table HI. The Size-Dependence of Peak Position of Excitonic Absorption Peak Positions ( Λ max) and These Energy Shift from Bulk Crystal ( Δ Ε ) of Various Microcrystals


Compound

CuCl

a

Inorganics CdSe

a

NTCDA/ PTCDA (Super lattice)

Crystal Size

^ max nm (cm )

ΔΕ

-1

/cm

-1

Bulk

386

(25900)

0

3.3 nm 2.1 nm Bulk 12 nm 1.8 nm

384 382 674 664 507

(26000) (26200) (14800) (15100) (19700)

100 300 0 300 4900

Bulk

560

(17860)

0

4 nm

558

(17900)

40

1 nm

555

(19000)

160

Bulk

(16130)

0

9 nm

(16210)

80

3 nm

(16390)

260

(20800) (21300) (22200) (15000) (15300)

0 500 1400 0 300

(15700)

700

Meas. Temp.

77 Κ

2K

b

c

PPy/PBT (Polymer Super Organics lattice)

d

Perylene

PDA (DCHD) a

b

c

d

Bulk 200 nm 50 nm Bulk 150 nm 50 nm

480 470 450 665 652 635

R.T.

R.T.

R.T.

R.T.

Ref. 20, 32. NTCDA (3, 4, 9, 10-perylenetetracarboxylic dianhydride), PTCDA (3, 4, 7, 8naphthalenetetracarboxylic dianhydride)(Ref. 34). PPy (polypyrrole), PBT (polybithiophene) These data were measured by photoluminescense.(Ref. 31). Ref. 33, 35.


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NAKANISHI & KASAI

2

T=T sin (A(|>/2) Δφ = 2Jtn L Ι/λ

(1) (2)

0

2

eff

where, T is the maximum possible transmittance, Δφ is the phase shift, I is the gate power intensity, and λ is the probe light wavelength. L is the effective medium length and is given by equation (3): 0

eff

aL

L ff.= a-e" )/a

(3)


e

where, a is the absorption loss, L is the medium length. The n value for the microcrystal dispersions can be calculated using n (cs2) reference sample from equation (4). 2

a s

a

2

Ι

\CSi)

Uff

(Γ/Γ0)

The relationship between n and yp^ is expressed by equation (5): 2

7

n = (8πχ® x 10 )/Cn

2

(5)

2

where C and η are light velocity and refractive index, respectively, χ ® is estimated from equation (6) which combines equations (4) and (5):

X

(3)

\cs2)^

Leff

' "(CS2)

Uif

-

1 (τ/το)

r'

T o

\c

( 6 )

S 2 )

of PDA Microcrystals in OKS Response. Table IV summarizes concentration (c), crystal size, and optical data of PDA microcrystal dispersions (36,37). Dispersion concentrations were of the order ΙΟ" M for the polydiacetylenes. Crystal size was diverse to some extent and Table IV lists representative values for each sample. The absorption maximum of dispersions of poly(l4-8ADA) is 645 nm. Those of poly(DCHD) varied depending on microcrystal size, i. e. absorption maxima of the crystals with 70, 100 and 150 nm in size are 640, 646 and 652 nm, respectively. Since there are no apparent absorption at both 813 and 1064 nm for these microcrystals, decrease of transmittance (T) is mainly due to scattering loss in the dispersion state. The transparency of poly(14-8ADA) dispersions at the wavelengths used is larger than that of poly(DCHD) dispersions. Enhancement by two-photon absorption can also be ignored because the transmittance did not change with increasing gate beam 3


196


intensity in the range used in this study. Thus, for a pulsed laser with a low repetition rate, thermal effect of the laser beam should be negligible under our experimental conditions. Table IV. Concentration(c), Crystal Size and Optical Data of PDA Microcrystals Dispersed in Water


Microcrystals

Crystal Tat Tat size 813 nm 1064 nm /% 1% /nm

^

Poly(14-8ADA) l.OxlO"

3

300

43

3)

*< /esu

/esuM'

1

>90

0.86xl0"

12

0.86xl0"

9

Poly(DCHD)

2.3xl0"

3

70

1.6

17

1.4 xlO"

12

0.61xl0"

9

Poly(DCHD)

2.3xl0"

3

100

1.6

17

2.2 xlO"

12

0.93xl0"

9

Poly(DCHD)

1.6xl0"

3

150

0.03

16

1.6 xlO"

12

1.0 xlO"

9

13

12

Measured χ ® values range from 10" to 10" esu and the largest χ ® is 2.2 x 10 esu for poly(DCHD) (37). This is slightly less than that of the maximum χ ® so far reported for organic dyes in solution. However, the χ ® values normalized by the concentration for the dispersion system are 10" esuM" , about two orders of magnitude larger than those for any other solution systems. These results suggest that microcrystal dispersion systems of large χ ® compounds are applicable for OKS materials when the concentration increases without increasing scattering loss. Though a size effect on absorption maximum has been observed for poly(DCHD) microcrystals, clear differences between yP^ values on these samples were not observed in this study. If the obtainable microcrystal size reaches several nanometers, quantum confinement effects which have been observed in inorganic semiconductors, may appear in these organic materials. Another virtue expected for microcrystal dispersion systems is ultrafast response since molecular orientation effects seem to be negligible due to the larger mass of microcrystals compared to molecules. However, in this study, it was impossible to measure the ultrafast response, because the pulse width of the laser used was of the order of 10" sec. This is currently under investigation. -12

9

1

9

CONCLUSIONS We have established an effective and simple method for preparing a variety of organic microcrystals in water. The solid-state polymerization of 4BCMU microcrystals was estimated to proceed from one end to the other end. The possibility of preparing PDAs with controlled molecular weight was qualitatively demonstrated. In the case of microcrystals of 14-8ADA, size-dependent conversion is found and can be explained by the looseness or thermal vibrations of the crystal lattice.


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Regarding the optical properties size was clearly found to affect the absorption maxima of PDA microcrystals. If crystal sizes down to several nanometers can be achieved, they are expected to show interesting nonlinear optical properties. Moreover, we found that organic microcrystal dispersions are applicable for OKS devices, with actual χ( ) values and those normalized by concentration for PDA dispersions are 10" ~ 10" esu and 10" esuM , respectively. Further efforts to increase dispersion concentration will establish microcrystallization as a new technique to incorprate crystalline compounds into large isotropic media. In addition, microcrystals composed of single chains of conjugated polymers from one end to the other could be useful for making molecular devices as well. 3


13

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ACKNOWLEDGEMENTS We thank Drs. H. Kanbara and T. Kaino for OKS measurements of PDA microcrystals and for useful discussions. We express our sincere gratitude to Dr. H. Matsuda, of National Institute of Materials and Chemical Reasearch; Drs. H. S. Nalwa and A. Kakuta, of Hitachi Labolatory; Drs. S. Okada, H. Oikawa, and R. Iida, of Institute for Chemical Reaction Science, Tohoku University, for collaborative research. These works were mostly supported by the Center for Interdisciplinary Research, Tokoku University and the New Energy Development Organization, MITI. LITERATURE CITED (1) Polydiacetylenes: Synthesis, Structure and Electronic Properties; Bloor, D.; Chance, R. R., Eds.; Martinus Nijhoff: Dordrecht, 1985. (2) Enkelmann,V.Adv. Polym. Sci. 1984, 63, 91. (3) Wegner, G. Z. Naturforsch 1969, 24b, 824. (4) Sauteret, C.; Hermann, J. P.; Frey, R.; Pradere F.; Ducuing, J.; Baughman, R. H.; Chance, R. R. Phys. Rev. Lett. 1976, 36, 956. (5) Etemad, S.; Baker, G. L.; Soos, Z. G. Molecular Nonlinear Optics; Zyss, J., Ed.; Academic Press: San Diego, 1994, p. 433. (6) Molyneux, S.; Matsuda, H; Kar, A. K.; Wherret, B. S.; Okada, S.; Nakanishi, H. Nonlinear Opt. 1993, 4, 299. (7) Kajzar F.; Messier, J. Polym. J. 1987, 19, 275. (8) Nakanishi, H.; Matsuda, H.; Okada, S.; Kato, M. Polym. Adv. Technol. 1990, 1, 75. (9) Kanbara, H.; Asobe, M.; Kubodera, K.; Kaino, T.; Kurihara, T. Appl. Phys. Lett. 1992, 61, 2290. (10) Townsend, P. D.; Jackel, J. L.; Baker, G. L.; Shelburne, J. Α.; Etemad, S. Appl. Phys. Lett. 1989, 55, 1829. (11) Duguay, Μ. Α.; Hansen, J. W. Appl. Phys. Lett. 1969, 15, 192.



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(12) Depasse, J.; Watilon, A.J. Collid Interface Sci. 1970, 33, 430. (13) van de Hulst, H. C. Light Scattering by Small Particles; Wiley: 1957. (14) Iijima, S.; Ichihashi, T. Jpn. J. Appl. Phys. 1985, 24, L125. (15) Iwama, S.; Hayakawa, K.; Arizumi, T. J.Cryst.Growth 1984, 66, 189. (16) Buffat, P.; Borel, J. P. Phys. Rev. A 1976, 13, 2287. (17) Hanamura, E. Phys. Rev. Β 1988, 37, 1273. (18) Brus, L. E. J. Chem. Phys. 1984, 80, 4403. (19) Ekimov, A. I.; Efros, Al. L.; Onushchenko, A. A. Solid State Commun. 1985, 56, 921. (20) Nakamura, Α.; Yamada, H.; Tokizaki, T. Phys. Rev. Β 1989, 40, 8585. (21) Wang, Y. J. Opt. Soc. Am. Β 1991, 8, 981. (22) Toyotama, H. Kinouzairyo 1987, 6, 44 (in Japanese). (23) Yase, K.; Inoue, T.; Okada, M.; Funada, T.; Hirano, J. Hyomen Kagaku 1989, 8, 434 (in Japanese). (24) Kasai, H.; Nalwa, H. S.; Oikawa, H.; Okada, S.; Matsuda, H.; Minami, N.; Kakuta, Α.; Ono, K.; Mukoh, A.; Nakanishi, H. Jpn. J. Appl. Phys., 1992, 31, L1132. (25) Chang, T. Y. Opt. Eng. 1981, 20, 220. (26) Kanbara, H.; Kobayashi, H.; Kaino, T.; Kurihara T.; Ooba, N. J. Opt. Soc. Am. B., in press. (27) Tieke, B.; Bloor, D.; Young, R. J. J. Mater. Sci. 1982, 17, 1156. (28) Iida, R.; Kamatani, H.; Kasai, H.; Okada, S.; Oikawa, H.; Matsuda, H.; Kakuta, Α.; Nakanishi, H. Mol. Cryst. Liq. Cryst. 1995, 267, 95. (29) Nalwa, H. S.; Kasai, H.; Okada, S.; Matsuda, H.; Oikawa, H.; Minami, N.; Kakuta, Α.; Ono, K.; Mukoh, Α.; Nakanishi, H. Polym. Adv. Technol. 1995, 6, 69. (30) Iida R., Master thesis, Tohoku Univ. (1994), to be published. (31) Fujitsuka, M.; Nakahara, R.; Iyoda, T.; Shimidzu, T.; Tsuchiya, H. J. Appl. Phys. 1993, 74, 1283. (32) Tokizaki, T.; Akiyama, H.; Tanaka, M.; Nakamura, A. J. Cryst. Growth 1992, 117, 603. (33) Nakanishi, H.; Kasai, H. Koubunshikakou 1996, 45, 15 (in Japanese). (34) So, F. F.; Forrest, S. R.; Shi, Y. Q.; Steier, W. H. Appl. Phys. Lett. 1990, 56, 674. (35) Kasai, H.; Kamatani, H.; Okada, S.; Oikawa, H.; Matsuda, H.; Nakanishi, H. Jpn. J. Appl. Phys. 1996, 35, L221. (36) Kasai, H.; Kanbara, H.; Iida, R.; Okada, S.; Matsuda, H.; Oikawa, H.; Nakanishi, H. Jpn. J. Appl. Phys. 1995, 34, L1208. (37) Kasai, H.; Iida, R.; Kanbara, H.; Okada, S.; Matsuda, H.; Oikawa, H.; Kaino, T.; Nakanishi, H. Nonlinear Opt. 1996, 15, 263.


Polydiacetylene Microcrystals for Third-Order Nonlinear Optics

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