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The structure and nonlinear optical properties of 3-n-propylamide-4-(4-hexyloxyphenylethynyl)-nitrobenzene
Journal of Molecular Structure 471 (1998) 139±143
The structure and nonlinear optical properties of 3-n-propylamide4-(4-hexyloxyphenylethynyl)-nitrobenzene Midori Kato a,*, Kimiko Kobayashi b, Masaaki Okunaka a,1, Nami Sugita a, Masashi Kiguchi a, Yoshio Taniguchi a,2 b
a Advanced Research Laboratory, Hitachi, Ltd., Hatoyama, Saitama 350-03, Japan The Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako-shi, Saitama 351-01, Japan
Received 23 February 1998; accepted 3 April 1998
Abstract We have synthesized the tolane derivative 3-n-propylamide-4-(4-hexyloxyphenylethynyl)-nitrobenzene 1 and examined its second-order nonlinear properties and crystal structure. Compound 1 crystallizes in the space group C1c1 with a 27.667(6), Ê , b 128.36(3)8 and Z 4, and shows a high second-order nonlinear optical ef®ciency. It has b 4.910(2), c 20.856(3) A an intermolecular hydrogen bond between CyO and N±H in the amide group. This hydrogen bond plays an important role in forming a non-centrosymmetric structure appropriate for nonlinear optical materials. q 1998 Elsevier Science B.V. All rights reserved Keywords: Nonlinear optics; Tolan; Hydrogen bond; Second-harmonic generation (SHG)
1. Introduction Many studies of new materials for nonlinear optics, especially about organic molecules, have been performed [1]. Among them tolane derivatives are regarded as promising materials for nonlinear optical use because of their large intramolecular charge transfer through the p -electron system with donor± acceptor groups and a low cut-off wavelength [2]. Accordingly, intensive studies have been conducted [2±5]. However, tolane derivatives tend to crystallize in centrosymmetric space groups [6], which causes the macroscopic second-order optical nonlinearity to * Corresponding author; e-mail: [email protected] 1 Present address: Production Engineering Research Laboratory, Hitachi Ltd., 292 Yoshida-cho, Totsuka-ku, Yokohama 244, Japan. 2 Present address: Department of Functional Polymer Science, Faculty of Science and Technology, Shinshu University, Ueda, Nagano 386, Japan.
vanish. The N±H stretching bond frequency, which is sensitive to the extent of hydrogen bonding of a group of tolane derivatives, has been examined, and the relation found between the frequency and the secondorder nonlinear optical activity [7]. A tolane derivative, ethyl 2-(4-benzyloxyphenylethynyl)-5-nitrobenzene-1-carbamate 2 (4-nitro-2-ethoxyamido-4 0 benzyloxytolane), has been studied and it was found that one phase of compound 2 has an intermolecular hydrogen bond and shows second-order nonlinear optical activity [8, 9]. We have synthesized a new tolane derivative, 3-n-propylamide-4-(4-hexyloxyphenylethynyl)-nitrobenzene 1 (4-nitro-2-n-propylamide-4 0 -hexyloxytolane, C24H28N2O4). The nonlinear optical study and the structural analysis of compound 1 could provide evidence supporting the hypothesis that the intermolecular hydrogen bond causes tolane derivatives to show macroscopic second-order optical nonlinearity.
0022-2860/98/$ - see front matter q 1998 Elsevier Science B.V. All rights reserved. PII S0 022-2860(98)004 01-3
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M. Kato et al. / Journal of Molecular Structure 471 (1998) 139±143
Fig. 1. SHEW signals of compound 1 and m-NA.
2. Experimental We prepared 4-hexyloxycinnamic acid by a reaction of 4-hexyloxy-benzaldehyde, which was prepared from 4-hydroxybenzaldehyde and n-hexyl bromide, with malonic acid. The acid was treated with bromine, followed by elimination of HBr in two steps, which resulted in the formation of 4-hexyloxyphenylacetylene. 3-n-Propylamide-4-bromonitrobenzene was Table 1 Crystallographic data of compound 1 FWD
408.48
Crystal system Space group Unit cell dimensions Ê) a (A Ê) b (A Ê) c (A b b(8) Ê 3) Unit cell volume U (A Z Dx (mg m 23) No. of unique re¯ections No. of re®ned parameters Criterion for observed re¯ections R Computer and programs
Monoclinic C1c1 27.667(6) 4.910(2) 20.856(3) 128.36(3) 2221.6(5.5) 4 1.221 2013 384 |Fo| . 4s (|Fo|) 0.058 FACOM M-1800, UNICS-III program system
Fig. 2. The title molecule with displacement ellipsoids plotted at the 50% probability level.
prepared by the reaction of 4-bromo-3-aminonitrobenzene with butyrylchloride. To form 3-n-propylamide4-(4-hexyloxyphenylethynyl)-nitrobenzene 1, 3-npropylamide-4-bromonitrobenzene and 4-hexyloxyphenylacetylene were reacted using CuI and PdCl2 (PPh3)2 in NEt3. The obtained material has a yellow color. Recrystallization was from ethanol, and the melting point was 398.5 K. We examined the nonlinear optical properties of this compound by second-harmonic generation with the evanescent wave (SHEW) technique. The details of this technique are described elsewhere [10]. It has an advantage of providing reasonable results even with powder samples because the phase-matchability of the sample does not affect the result. The experiment was performed with the fundamental light of a Nd:YAG laser (l 1064 nm). The fundamental light was guided into a rutile prism at an incident angle
M. Kato et al. / Journal of Molecular Structure 471 (1998) 139±143 Table 2 Selected bond lengths of compound 1 Bond
Ê) Length (A
Bond
Ê) Length (A
O(20)±C(16) O(23)±N(21) O(24)±C(25) N(15)±C(16) N(21)±C(5) C(1)±C(8) C(2)±C(7) C(4)±C(5) C(6)±C(7) C(9)±C(10) C(10)±C(11) C(12)±C(13) C(16)±C(17) C(18)±C(19) C(26)±C(27) C(28)±C(29)
1.221(0.006) 1.220(0.010) 1.434(0.010) 1.356(0.006) 1.480(0.009) 1.178(0.009) 1.418(0.006) 1.388(0.006) 1.381(0.010) 1.417(0.007) 1.368(0.009) 1.394(0.007) 1.526(0.006) 1.536(0.008) 1.529(0.013) 1.474(0.009)
O(22)±N(21) O(24)±C(12) N(15)±C(3) N(15)±H(N15) C(1)±C(2) C(2)±C(3) C(3)±C(4) C(5)±C(6) C(8)±C(9) C(9)±C(14) C(11)±C(12) C(13)±C(14) C(17)±C(18) C(25)±C(26) C(27)±C(28) C(29)±C(30)
1.219(0.006) 1.357(0.007) 1.411(0.005) 0.906(0.060) 1.433(0.009) 1.401(0.009) 1.376(0.008) 1.378(0.010) 1.438(0.008) 1.393(0.010) 1.402(0.011) 1.383(0.009) 1.507(0.009) 1.520(0.008) 1.538(0.009) 1.528(0.010)
such that the fundamental light was totally re¯ected at the interface between the prism and sample. The second-harmonic (SH) power in re¯ection was detected and compared with that from the reference material, meta-nitroaniline (m-NA). Single crystals of 1 for X-ray diffraction were
141
grown from an ethanol solution by the cooling method. The obtained single crystal has a thin plate shape. Data collection of X-ray diffraction was carried out with CAD-4 Software, the cell re®nement with CAD-4 Software, and data reduction with CAD-4 Software (all from Enraf Nonius). The program used to solve the structure was MULTAN78 [11] and the program used to re®ne the structure was UNICS-III [12]. Crystallographic data (excluding structure factors) for the structure in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC 101883. Copies of the data can be obtained, free of charge, on application to: CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail: deposit@ccdc,cam.ac.uk. 3. Results and discussion The SHEW signal of 1 is represented as circles in Fig. 1 with the signal of m-NA represented as diamonds. The solid curves represent the ®tting curves. The value of the susceptibility is calculated as a ®tting parameter and the value is compared with
Table 3 Selected bond angles of compound 1 Bonds
Angle (8)
Bonds
Angle (8)
C(12)±O(24)±C(25) C(3)±N(15)±H(N15) O(22)±N(21)±O(23) O(23)±N(21)±C(5) C(1)±C(2)±C(3) C(3)±C(2)±C(7) N(15)±C(3)±C(4) C(3)±C(4)±C(5) N(21)±C(5)±C(6) C(5)±C(6)±C(7) C(1)±C(8)±C(9) C(8)±C(9)±C(14) C(9)±C(10)±C(11) O(24)±C(12)±C(11) C(11)±C(12)±C(13) C(9)±C(14)±C(13) O(20)±C(16)±C(17) C(16)±C(17)±C(18) O(24)±C(25)±C(26) C(26)±C(27)±C(28) C(28)±C(29)±C(30)
117.9(0.4) 122.9(3.3) 123.7(0.7) 118.7(0.5) 119.5(0.4) 118.9(0.6) 121.2(0.5) 117.5(0.6) 118.9(0.4) 118.2(0.4) 177.1(0.7) 122.6(0.5) 120.6(0.7) 115.1(0.4) 119.7(0.6) 121.5(0.5) 123.8(0.4) 113.3(0.5) 107.1(0.5) 112.0(0.6) 112.7(0.6)
C(3)±N(15)±C(16) C(16)±N(15)±H(N15) O(22)±N(21)±C(5) C(2)±C(1)±C(8) C(1)±C(2)±C(7) N(15)±C(3)±C(2) C(2)±C(3)±C(4) N(21)±C(5)±C(4) C(4)±C(5)±C(6) C(2)±C(7)±C(6) C(8)±C(9)±C(10) C(10)±C(9)±C(14) C(10)±C(11)±C(12) O(24)±C(12)±C(13) C(12)±C(13)±C(14) O(20)±C(16)±N(15) N(15)±C(16)±C(17) C(17)±C(18)±C(19) C(25)±C(26)±C(27) C(27)±C(28)±C(29)
126.5(0.4) 109.6(3.1) 117.6(0.6) 172.0(0.6) 121.6(0.6) 117.4(0.5) 121.4(0.4) 117.3(0.6) 123.8(0.6) 120.3(0.6) 119.2(0.7) 118.2(0.5) 120.5(0.5) 125.2(0.7) 119.6(0.7) 123.0(0.4) 113.1(0.4) 111.0(0.6) 110.8(0.6) 117.5(0.7)
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M. Kato et al. / Journal of Molecular Structure 471 (1998) 139±143
Fig. 3. Crystal structure projected along the c-axis. For clarity, only half of the atoms in the unit cell are drawn. The hydrogen bonds are shown as dashed lines.
that of m-NA. Although the susceptibility is a tensor, we can obtain only one value from the powder sample, the averaged value of every tensor element over the whole solid angle. The details of the averaging are described in the Ref. [6]. The averaged susceptibility of m-NA is 11 pm/V using the value 0.364 pm/V of d11 of quartz [13]. Using this, the averaged value of 1 is estimated to be 23 ^ 2 pm/V, which is twice as large as that of m-NA. This is of the same order as 2 [9]. The results of the X-ray structure analysis are summarized in Table 1. The selected bond lengths and the angles are summarized in Tables 2 and 3. The molecular structure of 1 is shown in Fig. 2. It is designed as a p -electron system with donor and acceptor groups suitable for large intramolecular charge-transfer. The two benzene rings are planar and the mean planes of the two-ring systems are inclined at 2.3(2)8, making them almost parallel. Thus, p -electrons can spread over the tolane structure and the charge can be easily transferred between the nitro and hexyloxy groups.
Fig. 4. Packing of the molecules viewed along (a) b-axis and (b) c-axis.
M. Kato et al. / Journal of Molecular Structure 471 (1998) 139±143
The hexyloxy group is in almost the same plane as the benzene rings except for C(29) and C(30). The conformation change at the end of the group is caused by the crystal packing. The plane formed by C(26)± C(27)±C(28) in the hexyloxy group is tilted from the mean plane of the two benzene rings at 20.7(6)8 and at 22.4(6)8. The amide group N(15)±C(16)±O(20) forms a plane tilted by 38.6(3)8 from the mean plane of the two benzene rings. Thus the amide group is located between molecules stacked parallel along the b-axis, permitting formation of the hydrogen bond (Fig. 3). The distance between O(20) and N(15) of the neighbor molecule by one unit cell Ê . The hydrogen along the b-axis is 2.967(5) A bond N(15)±H(N15)¼O(20) is formed between the neighboring molecules. The angle for the hydrogen bond was found to be 146.4(4)8. It has been indicated that tolane derivatives with hydrogen bonding between molecules tend to have high nonlinear optical susceptibilities [7] because the hydrogen bonding is expected to break the centrosymmetry structure. Thus, for this derivative 1, which shows large SHG ef®ciency as shown below, hydrogen bonding plays an important role in its second-order nonlinear properties. The mean plane of the tolane structure, which is formed by the two benzene rings and the triple bond between C(1) and C(8), is tilted from the ab, ca, and bc planes at 83.8(1), 42.3(1) and 117.0(1)8, respectively. The mean planes of tolane of the two molecules in symmetry (x, 2 y, z 1 1/2) are tilted 87.7(1)8, as shown in Fig. 4. As expected from the SHEW results, the molecular structure and packing of 1 are very similar to those of 2 [8]. Thus, the molecular packing of 1 and 2, which contains the intermolecular hydrogen bond, is the key to have a large second-order nonlinear optical susceptibility. 4. Conclusion We have synthesized the novel nonlinear optical
143
material 3-n-propylamide-4-(4-hexyloxyphenylethynyl)-nitrobenzene, examined its second-order nonlinear optical properties, and determined its structure. Its second-order nonlinear optical susceptibility was found to be twice as large as that of m-NA, and the structure was very similar to other tolane derivatives, which also have large SHG ef®ciency. The intermolecular hydrogen bond was found to be formed in the amide group, suggesting that an amide group is required for the tolane derivatives to be SH active. Acknowledgements We would like to thank Dr. Angel Alvarez-Larena of Universidad de Autonoma de Barcelona for his useful discussions. References [1] D.S. Chemla, J. Zyss (Eds.), Nonlinear Optical Properties of Organic Molecules and Crystals. Academic Press, Orlando, 1987. [2] T. Kurihara, H. Tabei, T. Kaino, J. Chem. Soc. Chem. Commun. 1987 (1987) 959. [3] A.E. Stiegman, E. Graham, K.J. Perry, L.R. Khundkar, L.-T. Cheng, J.W. Perry, J. Am. Chem. Soc. 113 (1991) 7658. [4] M. Nakano, K. Yamaguchi, T. Fueno, Springer Proc. Phys. Nonlinear Optics Organics Semiconductors 36 (1989) 98. [5] N. Matsuzawa, D.A. Dixon, J. Phys. Chem. 96 (1992) 6232. [6] E. Graham, V.M. Miskowski, J.W. Perry, D.R. Coulter, A.E. Stiegman, W.P. Schaefer, R.E. Marsh, J. Am. Chem. Soc. 111 (1989) 8771. [7] M. Kato, M. Okunaka, N. Sugita, M. Kiguchi, Y. Taniguchi, Bull. Chem. Soc. Jpn. 70 (1997) 583. [8] M. Kato, K. Kobayashi, M. Kiguchi, N. Sugita, M. Okunaka, Y. Taniguchi, J. Mater. Chem. 7 (1997) 705. [9] M. Kato, M. Kiguchi, J. Appl. Phys. 81 (1997) 550. [10] M. Kiguchi, M. Kato, N. Kumegawa, Y. Taniguchi, J. Appl. Phys. 75 (1994) 4332. [11] P. Main, S.E. Hull, L. Lessinger, G. Germain, J.-P. Declercq, M.M. Woolfson, MULTAN. A Program for the Automatic Solution of Crystal Structures from X-ray Diffraction Data, University of York, England, and Louvain, Belgium. 1978. [12] T. Sakurai, K. Kobayashi, Rikagaku Kenkyusho Hokoku (in Japanese) 55 (1979) 69. [13] Handbook of Lasers, Chemical Rubber Co., Cleveland, OH, 1971, p. 497.
The structure and nonlinear optical properties of 3-n-propylamide4-(4-hexyloxyphenylethynyl)-nitrobenzene Midori Kato a,*, Kimiko Kobayashi b, Masaaki Okunaka a,1, Nami Sugita a, Masashi Kiguchi a, Yoshio Taniguchi a,2 b
a Advanced Research Laboratory, Hitachi, Ltd., Hatoyama, Saitama 350-03, Japan The Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako-shi, Saitama 351-01, Japan
Received 23 February 1998; accepted 3 April 1998
Abstract We have synthesized the tolane derivative 3-n-propylamide-4-(4-hexyloxyphenylethynyl)-nitrobenzene 1 and examined its second-order nonlinear properties and crystal structure. Compound 1 crystallizes in the space group C1c1 with a 27.667(6), Ê , b 128.36(3)8 and Z 4, and shows a high second-order nonlinear optical ef®ciency. It has b 4.910(2), c 20.856(3) A an intermolecular hydrogen bond between CyO and N±H in the amide group. This hydrogen bond plays an important role in forming a non-centrosymmetric structure appropriate for nonlinear optical materials. q 1998 Elsevier Science B.V. All rights reserved Keywords: Nonlinear optics; Tolan; Hydrogen bond; Second-harmonic generation (SHG)
1. Introduction Many studies of new materials for nonlinear optics, especially about organic molecules, have been performed [1]. Among them tolane derivatives are regarded as promising materials for nonlinear optical use because of their large intramolecular charge transfer through the p -electron system with donor± acceptor groups and a low cut-off wavelength [2]. Accordingly, intensive studies have been conducted [2±5]. However, tolane derivatives tend to crystallize in centrosymmetric space groups [6], which causes the macroscopic second-order optical nonlinearity to * Corresponding author; e-mail: [email protected] 1 Present address: Production Engineering Research Laboratory, Hitachi Ltd., 292 Yoshida-cho, Totsuka-ku, Yokohama 244, Japan. 2 Present address: Department of Functional Polymer Science, Faculty of Science and Technology, Shinshu University, Ueda, Nagano 386, Japan.
vanish. The N±H stretching bond frequency, which is sensitive to the extent of hydrogen bonding of a group of tolane derivatives, has been examined, and the relation found between the frequency and the secondorder nonlinear optical activity [7]. A tolane derivative, ethyl 2-(4-benzyloxyphenylethynyl)-5-nitrobenzene-1-carbamate 2 (4-nitro-2-ethoxyamido-4 0 benzyloxytolane), has been studied and it was found that one phase of compound 2 has an intermolecular hydrogen bond and shows second-order nonlinear optical activity [8, 9]. We have synthesized a new tolane derivative, 3-n-propylamide-4-(4-hexyloxyphenylethynyl)-nitrobenzene 1 (4-nitro-2-n-propylamide-4 0 -hexyloxytolane, C24H28N2O4). The nonlinear optical study and the structural analysis of compound 1 could provide evidence supporting the hypothesis that the intermolecular hydrogen bond causes tolane derivatives to show macroscopic second-order optical nonlinearity.
0022-2860/98/$ - see front matter q 1998 Elsevier Science B.V. All rights reserved. PII S0 022-2860(98)004 01-3
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M. Kato et al. / Journal of Molecular Structure 471 (1998) 139±143
Fig. 1. SHEW signals of compound 1 and m-NA.
2. Experimental We prepared 4-hexyloxycinnamic acid by a reaction of 4-hexyloxy-benzaldehyde, which was prepared from 4-hydroxybenzaldehyde and n-hexyl bromide, with malonic acid. The acid was treated with bromine, followed by elimination of HBr in two steps, which resulted in the formation of 4-hexyloxyphenylacetylene. 3-n-Propylamide-4-bromonitrobenzene was Table 1 Crystallographic data of compound 1 FWD
408.48
Crystal system Space group Unit cell dimensions Ê) a (A Ê) b (A Ê) c (A b b(8) Ê 3) Unit cell volume U (A Z Dx (mg m 23) No. of unique re¯ections No. of re®ned parameters Criterion for observed re¯ections R Computer and programs
Monoclinic C1c1 27.667(6) 4.910(2) 20.856(3) 128.36(3) 2221.6(5.5) 4 1.221 2013 384 |Fo| . 4s (|Fo|) 0.058 FACOM M-1800, UNICS-III program system
Fig. 2. The title molecule with displacement ellipsoids plotted at the 50% probability level.
prepared by the reaction of 4-bromo-3-aminonitrobenzene with butyrylchloride. To form 3-n-propylamide4-(4-hexyloxyphenylethynyl)-nitrobenzene 1, 3-npropylamide-4-bromonitrobenzene and 4-hexyloxyphenylacetylene were reacted using CuI and PdCl2 (PPh3)2 in NEt3. The obtained material has a yellow color. Recrystallization was from ethanol, and the melting point was 398.5 K. We examined the nonlinear optical properties of this compound by second-harmonic generation with the evanescent wave (SHEW) technique. The details of this technique are described elsewhere [10]. It has an advantage of providing reasonable results even with powder samples because the phase-matchability of the sample does not affect the result. The experiment was performed with the fundamental light of a Nd:YAG laser (l 1064 nm). The fundamental light was guided into a rutile prism at an incident angle
M. Kato et al. / Journal of Molecular Structure 471 (1998) 139±143 Table 2 Selected bond lengths of compound 1 Bond
Ê) Length (A
Bond
Ê) Length (A
O(20)±C(16) O(23)±N(21) O(24)±C(25) N(15)±C(16) N(21)±C(5) C(1)±C(8) C(2)±C(7) C(4)±C(5) C(6)±C(7) C(9)±C(10) C(10)±C(11) C(12)±C(13) C(16)±C(17) C(18)±C(19) C(26)±C(27) C(28)±C(29)
1.221(0.006) 1.220(0.010) 1.434(0.010) 1.356(0.006) 1.480(0.009) 1.178(0.009) 1.418(0.006) 1.388(0.006) 1.381(0.010) 1.417(0.007) 1.368(0.009) 1.394(0.007) 1.526(0.006) 1.536(0.008) 1.529(0.013) 1.474(0.009)
O(22)±N(21) O(24)±C(12) N(15)±C(3) N(15)±H(N15) C(1)±C(2) C(2)±C(3) C(3)±C(4) C(5)±C(6) C(8)±C(9) C(9)±C(14) C(11)±C(12) C(13)±C(14) C(17)±C(18) C(25)±C(26) C(27)±C(28) C(29)±C(30)
1.219(0.006) 1.357(0.007) 1.411(0.005) 0.906(0.060) 1.433(0.009) 1.401(0.009) 1.376(0.008) 1.378(0.010) 1.438(0.008) 1.393(0.010) 1.402(0.011) 1.383(0.009) 1.507(0.009) 1.520(0.008) 1.538(0.009) 1.528(0.010)
such that the fundamental light was totally re¯ected at the interface between the prism and sample. The second-harmonic (SH) power in re¯ection was detected and compared with that from the reference material, meta-nitroaniline (m-NA). Single crystals of 1 for X-ray diffraction were
141
grown from an ethanol solution by the cooling method. The obtained single crystal has a thin plate shape. Data collection of X-ray diffraction was carried out with CAD-4 Software, the cell re®nement with CAD-4 Software, and data reduction with CAD-4 Software (all from Enraf Nonius). The program used to solve the structure was MULTAN78 [11] and the program used to re®ne the structure was UNICS-III [12]. Crystallographic data (excluding structure factors) for the structure in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC 101883. Copies of the data can be obtained, free of charge, on application to: CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail: deposit@ccdc,cam.ac.uk. 3. Results and discussion The SHEW signal of 1 is represented as circles in Fig. 1 with the signal of m-NA represented as diamonds. The solid curves represent the ®tting curves. The value of the susceptibility is calculated as a ®tting parameter and the value is compared with
Table 3 Selected bond angles of compound 1 Bonds
Angle (8)
Bonds
Angle (8)
C(12)±O(24)±C(25) C(3)±N(15)±H(N15) O(22)±N(21)±O(23) O(23)±N(21)±C(5) C(1)±C(2)±C(3) C(3)±C(2)±C(7) N(15)±C(3)±C(4) C(3)±C(4)±C(5) N(21)±C(5)±C(6) C(5)±C(6)±C(7) C(1)±C(8)±C(9) C(8)±C(9)±C(14) C(9)±C(10)±C(11) O(24)±C(12)±C(11) C(11)±C(12)±C(13) C(9)±C(14)±C(13) O(20)±C(16)±C(17) C(16)±C(17)±C(18) O(24)±C(25)±C(26) C(26)±C(27)±C(28) C(28)±C(29)±C(30)
117.9(0.4) 122.9(3.3) 123.7(0.7) 118.7(0.5) 119.5(0.4) 118.9(0.6) 121.2(0.5) 117.5(0.6) 118.9(0.4) 118.2(0.4) 177.1(0.7) 122.6(0.5) 120.6(0.7) 115.1(0.4) 119.7(0.6) 121.5(0.5) 123.8(0.4) 113.3(0.5) 107.1(0.5) 112.0(0.6) 112.7(0.6)
C(3)±N(15)±C(16) C(16)±N(15)±H(N15) O(22)±N(21)±C(5) C(2)±C(1)±C(8) C(1)±C(2)±C(7) N(15)±C(3)±C(2) C(2)±C(3)±C(4) N(21)±C(5)±C(4) C(4)±C(5)±C(6) C(2)±C(7)±C(6) C(8)±C(9)±C(10) C(10)±C(9)±C(14) C(10)±C(11)±C(12) O(24)±C(12)±C(13) C(12)±C(13)±C(14) O(20)±C(16)±N(15) N(15)±C(16)±C(17) C(17)±C(18)±C(19) C(25)±C(26)±C(27) C(27)±C(28)±C(29)
126.5(0.4) 109.6(3.1) 117.6(0.6) 172.0(0.6) 121.6(0.6) 117.4(0.5) 121.4(0.4) 117.3(0.6) 123.8(0.6) 120.3(0.6) 119.2(0.7) 118.2(0.5) 120.5(0.5) 125.2(0.7) 119.6(0.7) 123.0(0.4) 113.1(0.4) 111.0(0.6) 110.8(0.6) 117.5(0.7)
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M. Kato et al. / Journal of Molecular Structure 471 (1998) 139±143
Fig. 3. Crystal structure projected along the c-axis. For clarity, only half of the atoms in the unit cell are drawn. The hydrogen bonds are shown as dashed lines.
that of m-NA. Although the susceptibility is a tensor, we can obtain only one value from the powder sample, the averaged value of every tensor element over the whole solid angle. The details of the averaging are described in the Ref. [6]. The averaged susceptibility of m-NA is 11 pm/V using the value 0.364 pm/V of d11 of quartz [13]. Using this, the averaged value of 1 is estimated to be 23 ^ 2 pm/V, which is twice as large as that of m-NA. This is of the same order as 2 [9]. The results of the X-ray structure analysis are summarized in Table 1. The selected bond lengths and the angles are summarized in Tables 2 and 3. The molecular structure of 1 is shown in Fig. 2. It is designed as a p -electron system with donor and acceptor groups suitable for large intramolecular charge-transfer. The two benzene rings are planar and the mean planes of the two-ring systems are inclined at 2.3(2)8, making them almost parallel. Thus, p -electrons can spread over the tolane structure and the charge can be easily transferred between the nitro and hexyloxy groups.
Fig. 4. Packing of the molecules viewed along (a) b-axis and (b) c-axis.
M. Kato et al. / Journal of Molecular Structure 471 (1998) 139±143
The hexyloxy group is in almost the same plane as the benzene rings except for C(29) and C(30). The conformation change at the end of the group is caused by the crystal packing. The plane formed by C(26)± C(27)±C(28) in the hexyloxy group is tilted from the mean plane of the two benzene rings at 20.7(6)8 and at 22.4(6)8. The amide group N(15)±C(16)±O(20) forms a plane tilted by 38.6(3)8 from the mean plane of the two benzene rings. Thus the amide group is located between molecules stacked parallel along the b-axis, permitting formation of the hydrogen bond (Fig. 3). The distance between O(20) and N(15) of the neighbor molecule by one unit cell Ê . The hydrogen along the b-axis is 2.967(5) A bond N(15)±H(N15)¼O(20) is formed between the neighboring molecules. The angle for the hydrogen bond was found to be 146.4(4)8. It has been indicated that tolane derivatives with hydrogen bonding between molecules tend to have high nonlinear optical susceptibilities [7] because the hydrogen bonding is expected to break the centrosymmetry structure. Thus, for this derivative 1, which shows large SHG ef®ciency as shown below, hydrogen bonding plays an important role in its second-order nonlinear properties. The mean plane of the tolane structure, which is formed by the two benzene rings and the triple bond between C(1) and C(8), is tilted from the ab, ca, and bc planes at 83.8(1), 42.3(1) and 117.0(1)8, respectively. The mean planes of tolane of the two molecules in symmetry (x, 2 y, z 1 1/2) are tilted 87.7(1)8, as shown in Fig. 4. As expected from the SHEW results, the molecular structure and packing of 1 are very similar to those of 2 [8]. Thus, the molecular packing of 1 and 2, which contains the intermolecular hydrogen bond, is the key to have a large second-order nonlinear optical susceptibility. 4. Conclusion We have synthesized the novel nonlinear optical
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material 3-n-propylamide-4-(4-hexyloxyphenylethynyl)-nitrobenzene, examined its second-order nonlinear optical properties, and determined its structure. Its second-order nonlinear optical susceptibility was found to be twice as large as that of m-NA, and the structure was very similar to other tolane derivatives, which also have large SHG ef®ciency. The intermolecular hydrogen bond was found to be formed in the amide group, suggesting that an amide group is required for the tolane derivatives to be SH active. Acknowledgements We would like to thank Dr. Angel Alvarez-Larena of Universidad de Autonoma de Barcelona for his useful discussions. References [1] D.S. Chemla, J. Zyss (Eds.), Nonlinear Optical Properties of Organic Molecules and Crystals. Academic Press, Orlando, 1987. [2] T. Kurihara, H. Tabei, T. Kaino, J. Chem. Soc. Chem. Commun. 1987 (1987) 959. [3] A.E. Stiegman, E. Graham, K.J. Perry, L.R. Khundkar, L.-T. Cheng, J.W. Perry, J. Am. Chem. Soc. 113 (1991) 7658. [4] M. Nakano, K. Yamaguchi, T. Fueno, Springer Proc. Phys. Nonlinear Optics Organics Semiconductors 36 (1989) 98. [5] N. Matsuzawa, D.A. Dixon, J. Phys. Chem. 96 (1992) 6232. [6] E. Graham, V.M. Miskowski, J.W. Perry, D.R. Coulter, A.E. Stiegman, W.P. Schaefer, R.E. Marsh, J. Am. Chem. Soc. 111 (1989) 8771. [7] M. Kato, M. Okunaka, N. Sugita, M. Kiguchi, Y. Taniguchi, Bull. Chem. Soc. Jpn. 70 (1997) 583. [8] M. Kato, K. Kobayashi, M. Kiguchi, N. Sugita, M. Okunaka, Y. Taniguchi, J. Mater. Chem. 7 (1997) 705. [9] M. Kato, M. Kiguchi, J. Appl. Phys. 81 (1997) 550. [10] M. Kiguchi, M. Kato, N. Kumegawa, Y. Taniguchi, J. Appl. Phys. 75 (1994) 4332. [11] P. Main, S.E. Hull, L. Lessinger, G. Germain, J.-P. Declercq, M.M. Woolfson, MULTAN. A Program for the Automatic Solution of Crystal Structures from X-ray Diffraction Data, University of York, England, and Louvain, Belgium. 1978. [12] T. Sakurai, K. Kobayashi, Rikagaku Kenkyusho Hokoku (in Japanese) 55 (1979) 69. [13] Handbook of Lasers, Chemical Rubber Co., Cleveland, OH, 1971, p. 497.