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[Zn(C7H3O5N)]n · nH2O: A third-order NLO Zn coordination polymer with spiroconjugated structure
Chemical Physics Letters 426 (2006) 341–344 www.elsevier.com/locate/cplett
[Zn(C7H3O5N)]n Æ nH2O: A third-order NLO Zn coordination polymer with spiroconjugated structure Guo-Wei Zhou a, You-Zhao Lan a, Fa-Kun Zheng a, Xin Zhang b, Meng-Hai Lin Guo-Cong Guo a,*, Jin-Shun Huang a a
b,*
,
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, PR China b Department of Chemistry, Xiamen University, Xiamen 361005, PR China Received 22 February 2006; in final form 2 June 2006 Available online 17 June 2006
Abstract [Zn(C7H3O5N)]n Æ nH2O (1) possesses an anticlockwise windmill-like framework structure and formats spiroconjugation over the infinite molecular layer that is predicted to have large static third-order polarizability and the convergence value of cxxxx reaches 6.86 · 10 33 esu in the case of zero input photon energy. The third-order NLO properties of 1 were investigated via Z-scan techniques at wavelength of 532 nm. It showed strong third-order NLO absorptive properties, and its n2 value was calculated to be 4.15 · 10 11 esu. The relationship between the spiroconjugated structure and the NLO property has been discussed, which supposed to be more valuable for the NLO research. 2006 Elsevier B.V. All rights reserved.
1. Introduction Design and synthesis of inorganic–organic hybrid materials have received more and more attention due to their potential applications in catalysis, electrics, magnetism and optics [1]. A large number of coordination polymers with interesting properties have been prepared and characterized, [2] among which, the coordination polymers with third-order NLO properties are of current topical interest [3]. Main strategy in the search of advanced non-linear organic materials concerning third-order susceptibilities consisted in the varying the number of branches of the benzene cycles, [4] application of nematic liquid crystals, [5] photoinduced treatment of the guest–host organic chromophore [6]. In 1967, Simmons and Hoffmann pointed out that the appearance of spiroconjugation in the molecular structure indicated well third-order NLO properties [7]. However, the instances of spiroconjugated polymer struc-
*
Corresponding authors. Fax: +86 591 83714946. E-mail address: [email protected] (G.-C. Guo).
0009-2614/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2006.06.034
ture with well third-order NLO properties were rarely reported [8]. We used zinc ion and chelidamic acid (2,6dicarboxy-4-hydroxypyridine) as raw stuffs to build spiroconjugated structures not only because of the popular utilization of zinc ion (e.g., in biochemistry [9]), but also because of the wide usage of chelidamic acid in areas such as biochemistry, organic chemistry, medical chemistry, etc. [10]. Herein, we report the synthesis of a spiroconjugated structure of [Zn(C7H3O5N)]n Æ nH2O (1) and discuss the relationship between the crystal structure of coordination polymer and the observed and calculated NLO properties. 2. Method 2.1. Synthesis Compound 1 was synthesized by the reaction of zinc acetate with chelidamic acid at the presence of ammonia in aqueous solution. A mixture of Zn(CH3COO)2 Æ 2H2O (0.2 mmol, white farina) and chelidamic acid (0.3 mmol, yellow farina) was dissolved in water (15 mL). After dropping 3 drops ammonia into the solution, heated it to 90 C
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and stirred it for about 2 h, then filtered the solution. The filtrate was allowed to stand at room temperature. Yellow crystals were obtained over a period of 2–3 days (yield 52%, based on Zn(CH3COO)2 Æ 2H2O). 2.2. X-ray single-crystal analysis Crystal data for 1: [Zn(C7H3O5N)]n Æ nH2O, M = 264.49, dimensions 0.44 · 0.27 · 0.11 mm3, tetragonal, space group P-421c, a = 10.0580(5), c = 16.6150(15), V = 1680.83(19) ˚ 3, Z = 8, qcal. = 2.090 mg m 3, l(Mo Ka) = 2.931 mm 1. A Of the 12249 reflections measured (3.18 6 h 6 27.48), 1927 independent reflections were used to solve the structure. Based on all these data and 137 refined parameters, R1 = 0.0338, -R2 = 0.1113, and goodness-of-fit on F2 is 1.003. Crystallographic data for the structural analysis has been deposited with the Cambridge Crystallographic Data Centre, CCDC No. 245226 for compound 1. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ UK (Fax: +44-1223-336033; e-mail: [email protected] or http://www.ccdc.cam.ac.uk). 2.3. Non-linear optical measurements
Fig. 1. Perspective view of the anticlockwise windmill-like tetranuclear unit of 1: Zn–N11 = 2.020(3), Zn–O11 = 2.166(3), Zn–O12b = 1.978(3), ˚ ; O11–Zn–O12b = 94.9(2), Zn–O13 = 2.253(3), Zn–O14a = 1.951(3) A O11–Zn–O14a = 94.8(2), O12b–Zn–O14a = 103.1(1), O12b–Zn– N11 = 120.8(1), O14a–Zn–N11 = 135.6(1) (a: y, +x, z; b: y, 1+x, z).
The third-order non-linear optical properties of 1 in DMF were investigated by using Z-scan technique. A Nd:YAG laser system (Continuum NP70) with pulse duration of 8 ns at wavelength of 532 nm was employed as the light source. The spatial profiles of the optical pulses were nearly Gaussian contribution. The pulse laser beam was focused onto a sample cell with a 30-cm focal-length lens. The input and output pulses’ energy was measured simultaneously by precision laser detectors (818J-09B, Newport Corp), which were linked to a computer through an RS232 interface. The NLO properties of the sample were manifested by moving the sample along the axis of the incident laser irradiance beam (z-direction) with respect to the focal point and with incident laser irradiance kept constant. An aperture of 2 mm radius was placed in front of the detector to measure the transmitted energy. 3. Results and discussion As shown in Fig. 1, X-ray single-crystal analysis reveals that in 1 the zinc(II) ion is five-coordinated by a tridentate chelating chelidamic acid ligand, which forms a HalfWrap-Like (H-W-L) unit, and two carboxylic oxygen atoms from the adjacent chelidamic acid molecules, respectively. The 2-D structure of 1 can be regarded as a traditional M–O–M network if we lose sight of the 4hydroxypyridine (M = Zn(II); O = carboxyl) (Fig. 2). But an interesting feature of spiroconjugation is observed while all parts of the chelidamic acid ligand are counted. In the H-W-L unit, the zinc(II) ion and the chelidamic acid ligand ˚ , that supare coplanar with a mean deviation of 0.059(1) A ports the existence of a delocalized p-bond over the molec-
Fig. 2. Framework topology of 1, in which the M stand for Zn(II) ions, the O for carboxyl, the sector for 4-hydroxypyridine and the red dashed circle for the topology of Fig. 1 (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).
ular plane, as shown in Fig. 3. As can be seen clearly in the dashed circle in Fig. 2, four adjacent H-W-L units, consisting an anticlockwise windmill-like tetranuclear unit as shown in Fig. 1, are spiroconjugated through a carboxylic
G.-W. Zhou et al. / Chemical Physics Letters 426 (2006) 341–344
343
Fig. 4. Convergence behavior of third-order polarizabilities in the static case.
Fig. 3. The delocalized p-bond over the molecular plane in the H-W-L unit.
O atom acting as the spiral atom to form an infinite delocalized p-bond systems in the ab plane, resulting in the formation of infinite spiroconjugation framework, which is theoretically predicted to have a high third-order polarizability. In addition, it is worth noting that compound 1 is also the first 2-D layer compound containing chelidamic acid ligand. As a result, this report is also a valuable work for the study of expanding the structure types of complexes of chelidamic acid. The density-functional study on the static third-order polarizability of 1 (Fig. 1 shows the molecular model and its orientation) was carried out by using the time-dependent density functional theory (TDDFT) at B3LYP/ LanL2DZ level in GAUSSIAN 03 program [11] combined with the sum-over-states method [12]. Note that, in the static case, in which input energy is equal to zero, the thirdorder non-linear optical polarizabilities for three optical processes: third-harmonic generation (THG), electricfield-induced second-harmonic generation (EFISHG) and degenerate four-wave mixing (DFWM) have the same value. The detailed computational process was described elsewhere [12,13]. Fig. 4 shows the plot of third-order polarizability convergence behavior in the static case. Note that, for the calculated model with S4 symmetry, the cxxxx is equal to cyyyy [14]. According to the data in Fig. 4, we can find that the convergence values of cxxxx and czzzz are 6.86 · 10 33 and 0.97 · 10 33 esu, respectively, which implies that the third-order polarizabilities along three orientations (Fig. 1) have a large value which is about three orders of magnitude greater than those of the reported general organic materials (10 36 esu) [15]. Additionally, the convergence values of cxxyy and cxxzz are 0.29 · 10 33 and 0.07 · 10 33 esu, respectively, which means that the c presents the strong anisotropy. The theoretical calculation
reveals the present compound is a very promising candidate for the third-order non-linear optics effect. The non-linear refractive components were assessed by dividing the normalized Z-scan data obtained under the closed aperture configuration by the normalized Z-scan data obtained under the open aperture configuration. Fig. 5 presents the typical NLO refractive data for 1. The data show that compound 1 has a positive sign for the non-linear refraction and exhibits strong self-focusing behavior. A reasonably good fit between the experimental data (black dot) and the theoretical curves (solids curves) based on Sheik-Bahae’s report was obtained [16]. The effective third-order refractive index n2 of 1 is calculated to be 4.15 · 10 11 esu. The third-order polarizability of 1 is 1.05 · 10 12 esu, which is comparable to the values
Fig. 5. Z-scan data for 1 in 2.0 · 10 4 mol dm 3 DMF solution, obtained by dividing the normalized Z-scan measured under a closed aperture configuration by the normalized Z-scan data obtained under the open aperture configuration. The black dots are the experimental data, and the solids curve is the theoretical fit.
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reported for the metal phthalocyanines, [3] as well as those from theoretical calculations [17]. In addition, in the solid state compound 1 exhibits intense photoluminescence upon photoexcitation at 304 nm (Fig. S1). The emission of 1 (kmax = 422 nm) may be assigned as ligand-to-metal charge transfer (LMCT) [18]. It may be a good candidate for applications on the making of blue-light emitting diode devices, since these condensed materials are insoluble in most polar and nonpolar solvents. In summary, we have reported the synthesis, crystal structure and optical properties of the inorganic–organic hybrid containing an anticlockwise windmill-like framework with spiroconjugation. In light of this work, a new family of hybrid materials with novel structures and NLO properties may be rationally designed and synthesized. Given the theoretical results of high third-order polarizabilities, the emergence of a large field of new and exciting optical materials may be expected. Synthesis of these materials is currently in process. Acknowledgements We gratefully acknowledge the financial support of the NSF of China (20571075), the NSF for Distinguished Young Scientist of China (20425104) and the NSF of Fujian Province (A0420002). Appendix A. Supplementary data Supplementary data associated with this Letter can be found, in the online version, at doi:10.1016/ j.cplett.2006.06.034. References [1] O. Sato, T. Iyoda, A. Fujishima, K. Hashimoto, Science 49 (1996) 271; B.L. Chen, M. Eddaoudi, S.T. Hyde, M. O’Keeffe, O.M. Yaghi, Science 291 (2001) 1021; D.B. Mitizi, Prog. Inorg. Chem. 48 (1999) 1. [2] M. Eddaoudi, D.B. Moler, H.L. Li, B.L. Chen, T.M. Reineke, M. O’Keeffe, O.M. Yaghi, Acc. Chem. Res. 34 (2001) 319; H.L. Li, M. Eddaoudi, M. O’Keeffe, O.M. Yaghi, Nature 402 (1999) 276.
[3] N.J. Long, Angew. Chem. Int. Ed. Engl. 34 (1995) 21; S. Shi, Contemp. Phys. 35 (1994) 21; S.P. Karna, A.T. Yeates, Non-linear Optical Material, American Chemical Society, Washington, DC, 1996; O.R. Evans, W.B. Lin, Chem. Mater. 13 (9) (2001) 3009; W.B. Lin, Z.Y. Wang, L. Ma, J. Am. Chem. Soc. 121 (1999) 11249. [4] I. Fuks-Janczarek, J.-M. Nunzi, B. Sahraoui, I.V. Kityk, J. Berdowski, A.M. Caminade, J.-P. Majoral, A.C. Martineau, P. Frere, J. Roncali. Opt. Commun. 209 (2002) 461. [5] B. Sahraoui, I. Fuks-Janczarek, S. Bartkiewicz, K. Matczyszyn, J. Mysliwiec, I.V. Kityk, J. Berdowski, E. Allard, J. Cousseau. Chem. Phys. Lett. 365 (2002) 327. [6] I.V. Kityk, I. Fuks-Janczarek, E. Gondek, J.H. Lin, N.D. Lai, C.C. Hsu, P. Szlachcic, Chem. Phys. Lett. 418 (2006) 281. [7] R. Hoffmann, A. Imamura, G.D. Zeiss, J. Am. Chem. Soc. 89 (1967) 5215; H.E. Simmons, T. Fukunaga, J. Am. Chem. Soc. 89 (1967) 5208. [8] P. Maslak, A. Chopra, C.R. Moylan, R. Wortmann, S. Lebus, A.L. Rheingold, G.P.A. Yap, J. Am. Chem. Soc. 118 (1996) 1471; P. Maslak, Adv. Mater. 6 (1994) 405; J. Abe, Y. Shirai, N. Nemoto, Y. Nagase, J. Phys. Chem. A. 101 (1997) 1; S.Y. Kim, M. Lee, B.H. Boo, J. Chem. Phys. 109 (1998) 2593; W. Fu, J.K. Feng, G.B. Pan, J. Mol. Struct. (Theochem) 545 (2001) 157; J.P. Jiang, Y.H. Lai, J. Am. Chem. Soc. 125 (2003) 14296. [9] D. Lu, M.A. Searles, A. Klug, Nature 426 (2003) 96. [10] D.L. Boger, J. Hong, M. Hikota, M. Ishida, J. Am. Chem. Soc. 121 (1999) 2471; T. Fessmann, J.D. Kilburn, Angew. Chem. Int. Ed. Engl. 38 (1999) 1993; S.W. Ng, J. Organomet. Chem. 585 (1999) 12; G.J. Bridger, R.T. Skerlj, S. Padmanabhan, S.A. Martellucci, G.W. Henson, S. Struyf, M. Witvrouw, D. Schols, E.D. Clercq, J. Med. Chem. 42 (19) (1999) 3971. [11] M.J. Frisch et al., Gaussian Inc., Pittsburgh, PA, 2003. [12] B.J. Orr, J.F. Ward, Mol. Phys. 20 (1971) 513; B.M. Pierce, J. Chem. Phys. 91 (1989) 791. [13] D.-S. Wu, W.-D. Cheng, H. Zhang, X.-D. Li, Y.-Z. Lan, D.-G. Chen, Y.-J. Gong, Y.-C. Zhang, Phys. Rev. B. 68 (2003) 125402. [14] R.W. Boy, Non-linear Optics, Academic, San Diego, CA, 1992. [15] J.L. Bre´das, C. Adant, P. Tackx, A. Persoons, B.M. Pierce, Chem. Rev. 94 (1994) 243. [16] M. Sheik-Bahae, A.A. Said, T.H. Wei, D.J. Hagan, E.W.V. Stryland, IEEE J. Quantum Electron. 26 (1990) 760. [17] W.-D. Cheng, D.-S. Wu, H. Zhang, J.-T. Chen, Phys. Rev. B. 64 (2001) 125109. [18] A. Meijerink, G. Blasse, M. Glasbeek, J. Phys.: Condens. Mat. 2 (1990) 6303; R. Bertoncello, M. Bettinelli, M. Cassrin, A. Gulino, E. Tondello, A. Vittadini, Inorg. Chem. 31 (1992) 1558.
[Zn(C7H3O5N)]n Æ nH2O: A third-order NLO Zn coordination polymer with spiroconjugated structure Guo-Wei Zhou a, You-Zhao Lan a, Fa-Kun Zheng a, Xin Zhang b, Meng-Hai Lin Guo-Cong Guo a,*, Jin-Shun Huang a a
b,*
,
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, PR China b Department of Chemistry, Xiamen University, Xiamen 361005, PR China Received 22 February 2006; in final form 2 June 2006 Available online 17 June 2006
Abstract [Zn(C7H3O5N)]n Æ nH2O (1) possesses an anticlockwise windmill-like framework structure and formats spiroconjugation over the infinite molecular layer that is predicted to have large static third-order polarizability and the convergence value of cxxxx reaches 6.86 · 10 33 esu in the case of zero input photon energy. The third-order NLO properties of 1 were investigated via Z-scan techniques at wavelength of 532 nm. It showed strong third-order NLO absorptive properties, and its n2 value was calculated to be 4.15 · 10 11 esu. The relationship between the spiroconjugated structure and the NLO property has been discussed, which supposed to be more valuable for the NLO research. 2006 Elsevier B.V. All rights reserved.
1. Introduction Design and synthesis of inorganic–organic hybrid materials have received more and more attention due to their potential applications in catalysis, electrics, magnetism and optics [1]. A large number of coordination polymers with interesting properties have been prepared and characterized, [2] among which, the coordination polymers with third-order NLO properties are of current topical interest [3]. Main strategy in the search of advanced non-linear organic materials concerning third-order susceptibilities consisted in the varying the number of branches of the benzene cycles, [4] application of nematic liquid crystals, [5] photoinduced treatment of the guest–host organic chromophore [6]. In 1967, Simmons and Hoffmann pointed out that the appearance of spiroconjugation in the molecular structure indicated well third-order NLO properties [7]. However, the instances of spiroconjugated polymer struc-
*
Corresponding authors. Fax: +86 591 83714946. E-mail address: [email protected] (G.-C. Guo).
0009-2614/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2006.06.034
ture with well third-order NLO properties were rarely reported [8]. We used zinc ion and chelidamic acid (2,6dicarboxy-4-hydroxypyridine) as raw stuffs to build spiroconjugated structures not only because of the popular utilization of zinc ion (e.g., in biochemistry [9]), but also because of the wide usage of chelidamic acid in areas such as biochemistry, organic chemistry, medical chemistry, etc. [10]. Herein, we report the synthesis of a spiroconjugated structure of [Zn(C7H3O5N)]n Æ nH2O (1) and discuss the relationship between the crystal structure of coordination polymer and the observed and calculated NLO properties. 2. Method 2.1. Synthesis Compound 1 was synthesized by the reaction of zinc acetate with chelidamic acid at the presence of ammonia in aqueous solution. A mixture of Zn(CH3COO)2 Æ 2H2O (0.2 mmol, white farina) and chelidamic acid (0.3 mmol, yellow farina) was dissolved in water (15 mL). After dropping 3 drops ammonia into the solution, heated it to 90 C
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G.-W. Zhou et al. / Chemical Physics Letters 426 (2006) 341–344
and stirred it for about 2 h, then filtered the solution. The filtrate was allowed to stand at room temperature. Yellow crystals were obtained over a period of 2–3 days (yield 52%, based on Zn(CH3COO)2 Æ 2H2O). 2.2. X-ray single-crystal analysis Crystal data for 1: [Zn(C7H3O5N)]n Æ nH2O, M = 264.49, dimensions 0.44 · 0.27 · 0.11 mm3, tetragonal, space group P-421c, a = 10.0580(5), c = 16.6150(15), V = 1680.83(19) ˚ 3, Z = 8, qcal. = 2.090 mg m 3, l(Mo Ka) = 2.931 mm 1. A Of the 12249 reflections measured (3.18 6 h 6 27.48), 1927 independent reflections were used to solve the structure. Based on all these data and 137 refined parameters, R1 = 0.0338, -R2 = 0.1113, and goodness-of-fit on F2 is 1.003. Crystallographic data for the structural analysis has been deposited with the Cambridge Crystallographic Data Centre, CCDC No. 245226 for compound 1. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ UK (Fax: +44-1223-336033; e-mail: [email protected] or http://www.ccdc.cam.ac.uk). 2.3. Non-linear optical measurements
Fig. 1. Perspective view of the anticlockwise windmill-like tetranuclear unit of 1: Zn–N11 = 2.020(3), Zn–O11 = 2.166(3), Zn–O12b = 1.978(3), ˚ ; O11–Zn–O12b = 94.9(2), Zn–O13 = 2.253(3), Zn–O14a = 1.951(3) A O11–Zn–O14a = 94.8(2), O12b–Zn–O14a = 103.1(1), O12b–Zn– N11 = 120.8(1), O14a–Zn–N11 = 135.6(1) (a: y, +x, z; b: y, 1+x, z).
The third-order non-linear optical properties of 1 in DMF were investigated by using Z-scan technique. A Nd:YAG laser system (Continuum NP70) with pulse duration of 8 ns at wavelength of 532 nm was employed as the light source. The spatial profiles of the optical pulses were nearly Gaussian contribution. The pulse laser beam was focused onto a sample cell with a 30-cm focal-length lens. The input and output pulses’ energy was measured simultaneously by precision laser detectors (818J-09B, Newport Corp), which were linked to a computer through an RS232 interface. The NLO properties of the sample were manifested by moving the sample along the axis of the incident laser irradiance beam (z-direction) with respect to the focal point and with incident laser irradiance kept constant. An aperture of 2 mm radius was placed in front of the detector to measure the transmitted energy. 3. Results and discussion As shown in Fig. 1, X-ray single-crystal analysis reveals that in 1 the zinc(II) ion is five-coordinated by a tridentate chelating chelidamic acid ligand, which forms a HalfWrap-Like (H-W-L) unit, and two carboxylic oxygen atoms from the adjacent chelidamic acid molecules, respectively. The 2-D structure of 1 can be regarded as a traditional M–O–M network if we lose sight of the 4hydroxypyridine (M = Zn(II); O = carboxyl) (Fig. 2). But an interesting feature of spiroconjugation is observed while all parts of the chelidamic acid ligand are counted. In the H-W-L unit, the zinc(II) ion and the chelidamic acid ligand ˚ , that supare coplanar with a mean deviation of 0.059(1) A ports the existence of a delocalized p-bond over the molec-
Fig. 2. Framework topology of 1, in which the M stand for Zn(II) ions, the O for carboxyl, the sector for 4-hydroxypyridine and the red dashed circle for the topology of Fig. 1 (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).
ular plane, as shown in Fig. 3. As can be seen clearly in the dashed circle in Fig. 2, four adjacent H-W-L units, consisting an anticlockwise windmill-like tetranuclear unit as shown in Fig. 1, are spiroconjugated through a carboxylic
G.-W. Zhou et al. / Chemical Physics Letters 426 (2006) 341–344
343
Fig. 4. Convergence behavior of third-order polarizabilities in the static case.
Fig. 3. The delocalized p-bond over the molecular plane in the H-W-L unit.
O atom acting as the spiral atom to form an infinite delocalized p-bond systems in the ab plane, resulting in the formation of infinite spiroconjugation framework, which is theoretically predicted to have a high third-order polarizability. In addition, it is worth noting that compound 1 is also the first 2-D layer compound containing chelidamic acid ligand. As a result, this report is also a valuable work for the study of expanding the structure types of complexes of chelidamic acid. The density-functional study on the static third-order polarizability of 1 (Fig. 1 shows the molecular model and its orientation) was carried out by using the time-dependent density functional theory (TDDFT) at B3LYP/ LanL2DZ level in GAUSSIAN 03 program [11] combined with the sum-over-states method [12]. Note that, in the static case, in which input energy is equal to zero, the thirdorder non-linear optical polarizabilities for three optical processes: third-harmonic generation (THG), electricfield-induced second-harmonic generation (EFISHG) and degenerate four-wave mixing (DFWM) have the same value. The detailed computational process was described elsewhere [12,13]. Fig. 4 shows the plot of third-order polarizability convergence behavior in the static case. Note that, for the calculated model with S4 symmetry, the cxxxx is equal to cyyyy [14]. According to the data in Fig. 4, we can find that the convergence values of cxxxx and czzzz are 6.86 · 10 33 and 0.97 · 10 33 esu, respectively, which implies that the third-order polarizabilities along three orientations (Fig. 1) have a large value which is about three orders of magnitude greater than those of the reported general organic materials (10 36 esu) [15]. Additionally, the convergence values of cxxyy and cxxzz are 0.29 · 10 33 and 0.07 · 10 33 esu, respectively, which means that the c presents the strong anisotropy. The theoretical calculation
reveals the present compound is a very promising candidate for the third-order non-linear optics effect. The non-linear refractive components were assessed by dividing the normalized Z-scan data obtained under the closed aperture configuration by the normalized Z-scan data obtained under the open aperture configuration. Fig. 5 presents the typical NLO refractive data for 1. The data show that compound 1 has a positive sign for the non-linear refraction and exhibits strong self-focusing behavior. A reasonably good fit between the experimental data (black dot) and the theoretical curves (solids curves) based on Sheik-Bahae’s report was obtained [16]. The effective third-order refractive index n2 of 1 is calculated to be 4.15 · 10 11 esu. The third-order polarizability of 1 is 1.05 · 10 12 esu, which is comparable to the values
Fig. 5. Z-scan data for 1 in 2.0 · 10 4 mol dm 3 DMF solution, obtained by dividing the normalized Z-scan measured under a closed aperture configuration by the normalized Z-scan data obtained under the open aperture configuration. The black dots are the experimental data, and the solids curve is the theoretical fit.
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reported for the metal phthalocyanines, [3] as well as those from theoretical calculations [17]. In addition, in the solid state compound 1 exhibits intense photoluminescence upon photoexcitation at 304 nm (Fig. S1). The emission of 1 (kmax = 422 nm) may be assigned as ligand-to-metal charge transfer (LMCT) [18]. It may be a good candidate for applications on the making of blue-light emitting diode devices, since these condensed materials are insoluble in most polar and nonpolar solvents. In summary, we have reported the synthesis, crystal structure and optical properties of the inorganic–organic hybrid containing an anticlockwise windmill-like framework with spiroconjugation. In light of this work, a new family of hybrid materials with novel structures and NLO properties may be rationally designed and synthesized. Given the theoretical results of high third-order polarizabilities, the emergence of a large field of new and exciting optical materials may be expected. Synthesis of these materials is currently in process. Acknowledgements We gratefully acknowledge the financial support of the NSF of China (20571075), the NSF for Distinguished Young Scientist of China (20425104) and the NSF of Fujian Province (A0420002). Appendix A. Supplementary data Supplementary data associated with this Letter can be found, in the online version, at doi:10.1016/ j.cplett.2006.06.034. References [1] O. Sato, T. Iyoda, A. Fujishima, K. Hashimoto, Science 49 (1996) 271; B.L. Chen, M. Eddaoudi, S.T. Hyde, M. O’Keeffe, O.M. Yaghi, Science 291 (2001) 1021; D.B. Mitizi, Prog. Inorg. Chem. 48 (1999) 1. [2] M. Eddaoudi, D.B. Moler, H.L. Li, B.L. Chen, T.M. Reineke, M. O’Keeffe, O.M. Yaghi, Acc. Chem. Res. 34 (2001) 319; H.L. Li, M. Eddaoudi, M. O’Keeffe, O.M. Yaghi, Nature 402 (1999) 276.
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