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inorganic hybrid nonlinear optical material containing two-dimensional spindle-type chromophores
Materials Letters 65 (2011) 1404–1406
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Prepare organic/inorganic hybrid nonlinear optical material containing two-dimensional spindle-type chromophores Xiaolong Zhang, Ming Li, Zuosen Shi ⁎, Zhanchen Cui ⁎⁎ State Key Lab of Supramolecular Structure & Materials, College of Chemistry, Jilin University, Changchun 130012, PR China
a r t i c l e
i n f o
Article history: Received 28 December 2010 Accepted 2 February 2011 Available online 21 February 2011 Keywords: Spindle-type chromophore FTIR Sol–gel preparation Electro-optic (EO) coefficient
a b s t r a c t In this paper, functionalized alkoxysilane dye (ICTES-STC) was formed by the reaction of two-dimensional spindle-type chromophores (STC) with 3-isocyanatopropyltriethoxysilane (ICTES). The transparent films having silica network matrix and covalently bonded chromophores were fabricated via the sol–gel process. From TGA thermogram, the initial decomposition temperature of the hybrid film was determined to be 269 °C. The electro-optic (EO) coefficient (r33) of the poled films was measured to be around 12 pm/V by Teng–Man technique. The thermal stability of the NLO coefficient of the film was investigated by the depoling experiment and temporal decay test, and the result showed that the hybrid film had a good thermal stability, implying its potential applications for EO devices. © 2011 Elsevier B.V. All rights reserved.
1. Introduction In the past decade, the design of new and more efficient organic materials for nonlinear optics (NLO) has interested many areas, such as chemistry, physics, and material science, because they offer many advantages over traditional inorganic crystals: organic materials present fast response time and their structures can be tailored in myriads of ways allowing to finely tune NLO properties for desired applications for telecommunications, optical computing, and optical data storage [1–3]. One of the often encountered challenges in making highly efficient EO materials is to develop NLO chromophores with excellent thermal stability [4–6]. To improve the thermal stability of NLO materials, the effective way is incorporating chromophores into the sol–gel matrix [7–10]. When the chromophores were covalently incorporated into silicon trialkoxide, a three-dimensional network was formed by the hydrolysis and condensation of the alkoxysilane dye. The choice and design of the chromophores are crucial because several key requirements must be satisfied, such as high NLO activity, high thermal stability, and the possibility of chemical functionalization for coupling. At present, the main chromophores employed in organic/inorganic hybrid NLO materials are the common push–pull type one-dimensional chromophores [11–13]. The hybrid systems containing twodimensional chromophores received little attention. In this work, we have designed and prepared a new sol–gel material containing two-dimensional spindle-type chromophores.
The chromophores are covalently attached to a polymerizable silane to yield a precursor which can be copolymerized with tetraalkoxysilane (TEOS) under sol–gel hydrolysis/condensation processing conditions to yield a hybrid material. The chemical structure of the sol–gel precursor containing the chromophores was shown in Scheme 1. Their structures were verified by FTIR and 1H-NMR. The thermal stability of the sol–gel film was discussed. 2. Experimental 2.1. Materials Tetrahydrofuran (THF) and triethylamine (TEA) were purified by fractional distillation over sodium. 3-isocyanatopropyltriethoxysilane (ICTES, TCI) and other reagents were of commercial quality and used as received. The synthesis of the chromophore STC was given in detail elsewhere [14]. 2.2. Measurements Nuclear magnetic resonance (NMR) spectra were recorded on a Bruker AVANCE NMR spectrometer. IR spectra were taken on an AVATAR 360 FTIR spectrometer. The decomposition temperature (TGA) of the samples was analyzed by using Perkin-Elmer TGA 7 thermogravimetric analyzer. 2.3. Synthesis of alkoxysilane dye (ICTES-STC)
⁎ Corresponding author. Tel.: + 86 431 85168217; fax: + 86 431 85193423. ⁎⁎Correspondence to: Z. Cui, College of Chemistry, Jilin University, 2699# Qianjin Road, Changchun 130012, PR China. Tel.: + 86 431 85168217; fax: + 86 431 85193423. E-mail addresses: [email protected] (Z. Shi), [email protected] (Z. Cui). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.02.014
Chromophores (0.3 g, 0.5 mmol), ICTES (0.49 g, 2 mmol) were dissolved in dry THF (20 mL) and purged with nitrogen for 30 min to remove the atmospheric moisture. Then triethylamine (TEA, 0.2 mL)
X. Zhang et al. / Materials Letters 65 (2011) 1404–1406
1405
Scheme 1. Synthetic route of ICTES-STC and hybrid materials.
was added. The reaction mixture was stirred and refluxed for 48 h in nitrogen atmosphere. The solution was poured into dried hexane, and the resulting red precipitate was collected by suction filtration. The product was dried under vacuum at room temperature for 6 h. ICTES-STC: yield: 57%. 1H-NMR (500 MHz, CDCl3, TMS): δ (ppm) 7.72(s, 1 H, Ar–Ar–Ar), 7.684(s, 1 H, Ar–Ar–Ar), 7.59(s, 1H, NH), 7.50–7.53(d, 4H,−OCH2–Ar), 7.47–7.49(d, 2H, N–Ar), 7.44–7.46 (d, 4H,−OCH2–Ar), 7.34–7.36(d, 2H, N–Ar), 7.13–7.15(d,1H, CH=CH–TDF), 7.09–7.11(d, 1H, CH=CH–TDF), 6.95–6.98(d, 1H, N–Ar– CH=CH), 6.91–6.94(d, 1H, N–Ar–CH=CH), 6.78(s, 1H, CH), 4.76–4.83(d, 4H, O–CH2), 3.81–3.85(m, 12H, SiOCH2), 3.21–3.25(m, 4H, NH–CH2), 3.04(s, 6H, CH3–N), 2.55(s, 2H,−CH2−), 2.24(s, 2H,−CH2−), 1.55(s, 4H, NHCH2–CH2), 1.26(m, 18H, SiOCH2CH3), 1.01(s, 6H, CH3–C), 0.64–0.66 (t, 4H, Si–CH2). IR (KBr, cm− 1): 3412(−NH), 2962, 2923(−CH2−, −CH3), 2218(−CN), 1717(C=O), 1605,1556(−Ar), 1077 (Si–O–C2H5).
Fig. 1. FTIR spectra of chromophre STC, ICTES-STC and hybrid film.
2.4. Films preparation To prepare the coating solution, the ICTES-STC was mixed with tetraethoxysilane (TEOS) at a 1:10 M in THF. Then acidic water (HCl, pH = 1) was added, and the H2O/Si molar ratio was 4:1. The reaction mixture was stirred for 6 h. Finally, the solution aged for 4 days to increase viscosity. The sol was filtered through a 0.22 μm Teflon membrane filter before spin-coating on the indium–tin–oxide (ITO) glass substrates. The coated films were dried in a vacuum oven at 60 °C for 4 h to remove the residual solvent. 3. Results and discussion The synthesis route of alkoxysilane dye ICTES-STC is shown in Scheme 1. The chromophore STC was reacted with ICTES in the presence of triethylamine as catalyst to give the alkoxysilane dye via a
Fig. 2. 1H-NMR spectra of alkoxysilane ICTES-STC.
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X. Zhang et al. / Materials Letters 65 (2011) 1404–1406
Fig. 3. TGA traces for chromophore STC and hybrid film.
Fig. 4. Decay of the EO coefficient of the poled film as a function of temperature.
urethane forming reaction. The organic/inorganic hybrid film was prepared by the hydrolysis of the alkoxysilane dye with TEOS. The chemical structures of the products were confirmed by FTIR and 1HNMR spectroscopy as shown in Figs. 1 and 2. In the IR spectrum of the chromophore, the absorption bands at 2218 and 1605 cm− 1 are attributed to the stretching vibration of the cyano group and benzene ring, respectively. For the alkoxysilane dye, these absorption bands exhibit no significant change, while the new absorption band at 1717 cm− 1 appears. This strong absorption band is ascribed to the carbonyl stretching vibration of the urethane. In addition, a new absorption band due to the Si–OC2H5 group emerges at 1077 cm− 1. Furthermore, a new triplet proton peak around 7.59 ppm in the 1H-NMR spectra is assigned to the proton of the secondary amino group in urethane. These results identify the reaction between the hydroxyl functional group and isocyanate group and the formation of the alkoxysilane dye. The thermal stability of the hybrid film and chromophore was determined by thermogravimetric analysis (TGA) under atmosphere. As shown in Fig. 3, the initial decomposition temperature of the hybrid film is 269 °C, higher than that of the chromophore (224 °C). This result indicates that the covalent linkage between the chromophore and silica matrix could prevent the decomposition of the chromophore. It means that the hybrid film should have a higher Td due to its cross-linked silicon oxygen network.
nonlinearity, which indicated that the organic/inorganic hybrid film had potential applications for EO devices.
3.1. Nonlinear optical properties The nonlinear EO coefficient of the hybrid film was measured by Teng–Man technique after poling [15]. By calibrating the r33 data versus the GaAs data, the EO coefficient of the film was calculated up to 12 pm/V. The stability of optical nonlinearity was investigated through a depoling experiment in which the decay EO coefficient r33(t)/r33(t0) was monitored as the poled film was heated at a rate of 2 °C/min from 30 to 210 °C. As shown in Fig. 4, the poled film exhibited an excellent thermal stability of optical nonlinearity. No significant decay of r33 value was observed below 130 °C. The results showed a good NLO performance and high stability of optical
4. Conclusion In this paper, the second-order nonlinear optical organic/inorganic hybrid film containing two-dimensional spindle-type chromophores was successfully prepared via the sol–gel process. After corona poling, the EO coefficient of the hybrid film was calculated to be around 12 pm/V. By anchoring the chromophores to the three-dimensional silica network by two points of attachment, the hybrid film exhibited excellent thermal stability. Acknowledgments This work was supported by the National Natural Science Foundation of China (Grant No. 20974036, 20921003), Science and Technology Development Project of Jilin Province (20090317). References [1] Kim SK, Hung YC, Seo BJ, Geary K, Yuan W, Bortnik B, et al. Appl Phys Lett 2005;87 061112-1-3. [2] Lee M, Katz HE, Erben C, Gill DM, Heber JD, Mcgee DJ, et al. Science 2002;298:1401–3. [3] Dalton LR, Steier WH, Robinson BH, Zhang C, Ren A, Garner S, et al. J Mater Chem 1999;9:1905–20. [4] Kang H, Evmenenko G, Marks TJ. J Am Chem Soc 2006;128:6194–205. [5] Liao Y, Eichinger BE, Firestone KA, Jen AK-Y, Dalton LR, Robinson BH, et al. J Am Chem Soc 2005;127:2758–66. [6] Jang SH, Luo J, Tucker NM, Leclercq A, Dalton LR, Jen AK-Y, et al. Chem Mater 2006;18:2982–8. [7] Cu YJ, Qian GD, Chen LJ, Wang ZY, Gao JK, Wang MQ. J Phys Chem B 2006;110:4105–10. [8] Wang SW, Zhao LS, Yang S, Pang SJ, Cui ZC. Mater Lett 2009;63:292–4. [9] Chen LJ, Qian GD, Jin XF, Cui YJ, Gao JK, Wang ZY, et al. J Phys Chem B 2007;111:3115–21. [10] Chen LJ, Qian GD, Cui YJ, Wang MQ. J Phys Chem B 2006;110:19176–82. [11] Yu JC, Qiu JY, Cui YJ, Hu JT, Liu LY, Qian GD, et al. Mater Lett 2009;63:2594–6. [12] Cui YJ, Li BZ, Yu C, Yu JC, Gao JK, Qian GD, et al. Thin Solid Films 2009;517:5075–8. [13] Jin XF, Cui YJ, Gao JK, Nie JJ, Qian GD. Thin Solid Films 2009;517:5079–83. [14] Zhang XL, Shi ZS, Li M, Wan Y, Zhao LS, Cui ZC, et al. Macromol Chem Phys, accepted for publication. doi:10.1002/macp.201000626. [15] Teng CC, Man HT. Appl Phys Lett 1990;56:1734–6.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Prepare organic/inorganic hybrid nonlinear optical material containing two-dimensional spindle-type chromophores Xiaolong Zhang, Ming Li, Zuosen Shi ⁎, Zhanchen Cui ⁎⁎ State Key Lab of Supramolecular Structure & Materials, College of Chemistry, Jilin University, Changchun 130012, PR China
a r t i c l e
i n f o
Article history: Received 28 December 2010 Accepted 2 February 2011 Available online 21 February 2011 Keywords: Spindle-type chromophore FTIR Sol–gel preparation Electro-optic (EO) coefficient
a b s t r a c t In this paper, functionalized alkoxysilane dye (ICTES-STC) was formed by the reaction of two-dimensional spindle-type chromophores (STC) with 3-isocyanatopropyltriethoxysilane (ICTES). The transparent films having silica network matrix and covalently bonded chromophores were fabricated via the sol–gel process. From TGA thermogram, the initial decomposition temperature of the hybrid film was determined to be 269 °C. The electro-optic (EO) coefficient (r33) of the poled films was measured to be around 12 pm/V by Teng–Man technique. The thermal stability of the NLO coefficient of the film was investigated by the depoling experiment and temporal decay test, and the result showed that the hybrid film had a good thermal stability, implying its potential applications for EO devices. © 2011 Elsevier B.V. All rights reserved.
1. Introduction In the past decade, the design of new and more efficient organic materials for nonlinear optics (NLO) has interested many areas, such as chemistry, physics, and material science, because they offer many advantages over traditional inorganic crystals: organic materials present fast response time and their structures can be tailored in myriads of ways allowing to finely tune NLO properties for desired applications for telecommunications, optical computing, and optical data storage [1–3]. One of the often encountered challenges in making highly efficient EO materials is to develop NLO chromophores with excellent thermal stability [4–6]. To improve the thermal stability of NLO materials, the effective way is incorporating chromophores into the sol–gel matrix [7–10]. When the chromophores were covalently incorporated into silicon trialkoxide, a three-dimensional network was formed by the hydrolysis and condensation of the alkoxysilane dye. The choice and design of the chromophores are crucial because several key requirements must be satisfied, such as high NLO activity, high thermal stability, and the possibility of chemical functionalization for coupling. At present, the main chromophores employed in organic/inorganic hybrid NLO materials are the common push–pull type one-dimensional chromophores [11–13]. The hybrid systems containing twodimensional chromophores received little attention. In this work, we have designed and prepared a new sol–gel material containing two-dimensional spindle-type chromophores.
The chromophores are covalently attached to a polymerizable silane to yield a precursor which can be copolymerized with tetraalkoxysilane (TEOS) under sol–gel hydrolysis/condensation processing conditions to yield a hybrid material. The chemical structure of the sol–gel precursor containing the chromophores was shown in Scheme 1. Their structures were verified by FTIR and 1H-NMR. The thermal stability of the sol–gel film was discussed. 2. Experimental 2.1. Materials Tetrahydrofuran (THF) and triethylamine (TEA) were purified by fractional distillation over sodium. 3-isocyanatopropyltriethoxysilane (ICTES, TCI) and other reagents were of commercial quality and used as received. The synthesis of the chromophore STC was given in detail elsewhere [14]. 2.2. Measurements Nuclear magnetic resonance (NMR) spectra were recorded on a Bruker AVANCE NMR spectrometer. IR spectra were taken on an AVATAR 360 FTIR spectrometer. The decomposition temperature (TGA) of the samples was analyzed by using Perkin-Elmer TGA 7 thermogravimetric analyzer. 2.3. Synthesis of alkoxysilane dye (ICTES-STC)
⁎ Corresponding author. Tel.: + 86 431 85168217; fax: + 86 431 85193423. ⁎⁎Correspondence to: Z. Cui, College of Chemistry, Jilin University, 2699# Qianjin Road, Changchun 130012, PR China. Tel.: + 86 431 85168217; fax: + 86 431 85193423. E-mail addresses: [email protected] (Z. Shi), [email protected] (Z. Cui). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.02.014
Chromophores (0.3 g, 0.5 mmol), ICTES (0.49 g, 2 mmol) were dissolved in dry THF (20 mL) and purged with nitrogen for 30 min to remove the atmospheric moisture. Then triethylamine (TEA, 0.2 mL)
X. Zhang et al. / Materials Letters 65 (2011) 1404–1406
1405
Scheme 1. Synthetic route of ICTES-STC and hybrid materials.
was added. The reaction mixture was stirred and refluxed for 48 h in nitrogen atmosphere. The solution was poured into dried hexane, and the resulting red precipitate was collected by suction filtration. The product was dried under vacuum at room temperature for 6 h. ICTES-STC: yield: 57%. 1H-NMR (500 MHz, CDCl3, TMS): δ (ppm) 7.72(s, 1 H, Ar–Ar–Ar), 7.684(s, 1 H, Ar–Ar–Ar), 7.59(s, 1H, NH), 7.50–7.53(d, 4H,−OCH2–Ar), 7.47–7.49(d, 2H, N–Ar), 7.44–7.46 (d, 4H,−OCH2–Ar), 7.34–7.36(d, 2H, N–Ar), 7.13–7.15(d,1H, CH=CH–TDF), 7.09–7.11(d, 1H, CH=CH–TDF), 6.95–6.98(d, 1H, N–Ar– CH=CH), 6.91–6.94(d, 1H, N–Ar–CH=CH), 6.78(s, 1H, CH), 4.76–4.83(d, 4H, O–CH2), 3.81–3.85(m, 12H, SiOCH2), 3.21–3.25(m, 4H, NH–CH2), 3.04(s, 6H, CH3–N), 2.55(s, 2H,−CH2−), 2.24(s, 2H,−CH2−), 1.55(s, 4H, NHCH2–CH2), 1.26(m, 18H, SiOCH2CH3), 1.01(s, 6H, CH3–C), 0.64–0.66 (t, 4H, Si–CH2). IR (KBr, cm− 1): 3412(−NH), 2962, 2923(−CH2−, −CH3), 2218(−CN), 1717(C=O), 1605,1556(−Ar), 1077 (Si–O–C2H5).
Fig. 1. FTIR spectra of chromophre STC, ICTES-STC and hybrid film.
2.4. Films preparation To prepare the coating solution, the ICTES-STC was mixed with tetraethoxysilane (TEOS) at a 1:10 M in THF. Then acidic water (HCl, pH = 1) was added, and the H2O/Si molar ratio was 4:1. The reaction mixture was stirred for 6 h. Finally, the solution aged for 4 days to increase viscosity. The sol was filtered through a 0.22 μm Teflon membrane filter before spin-coating on the indium–tin–oxide (ITO) glass substrates. The coated films were dried in a vacuum oven at 60 °C for 4 h to remove the residual solvent. 3. Results and discussion The synthesis route of alkoxysilane dye ICTES-STC is shown in Scheme 1. The chromophore STC was reacted with ICTES in the presence of triethylamine as catalyst to give the alkoxysilane dye via a
Fig. 2. 1H-NMR spectra of alkoxysilane ICTES-STC.
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X. Zhang et al. / Materials Letters 65 (2011) 1404–1406
Fig. 3. TGA traces for chromophore STC and hybrid film.
Fig. 4. Decay of the EO coefficient of the poled film as a function of temperature.
urethane forming reaction. The organic/inorganic hybrid film was prepared by the hydrolysis of the alkoxysilane dye with TEOS. The chemical structures of the products were confirmed by FTIR and 1HNMR spectroscopy as shown in Figs. 1 and 2. In the IR spectrum of the chromophore, the absorption bands at 2218 and 1605 cm− 1 are attributed to the stretching vibration of the cyano group and benzene ring, respectively. For the alkoxysilane dye, these absorption bands exhibit no significant change, while the new absorption band at 1717 cm− 1 appears. This strong absorption band is ascribed to the carbonyl stretching vibration of the urethane. In addition, a new absorption band due to the Si–OC2H5 group emerges at 1077 cm− 1. Furthermore, a new triplet proton peak around 7.59 ppm in the 1H-NMR spectra is assigned to the proton of the secondary amino group in urethane. These results identify the reaction between the hydroxyl functional group and isocyanate group and the formation of the alkoxysilane dye. The thermal stability of the hybrid film and chromophore was determined by thermogravimetric analysis (TGA) under atmosphere. As shown in Fig. 3, the initial decomposition temperature of the hybrid film is 269 °C, higher than that of the chromophore (224 °C). This result indicates that the covalent linkage between the chromophore and silica matrix could prevent the decomposition of the chromophore. It means that the hybrid film should have a higher Td due to its cross-linked silicon oxygen network.
nonlinearity, which indicated that the organic/inorganic hybrid film had potential applications for EO devices.
3.1. Nonlinear optical properties The nonlinear EO coefficient of the hybrid film was measured by Teng–Man technique after poling [15]. By calibrating the r33 data versus the GaAs data, the EO coefficient of the film was calculated up to 12 pm/V. The stability of optical nonlinearity was investigated through a depoling experiment in which the decay EO coefficient r33(t)/r33(t0) was monitored as the poled film was heated at a rate of 2 °C/min from 30 to 210 °C. As shown in Fig. 4, the poled film exhibited an excellent thermal stability of optical nonlinearity. No significant decay of r33 value was observed below 130 °C. The results showed a good NLO performance and high stability of optical
4. Conclusion In this paper, the second-order nonlinear optical organic/inorganic hybrid film containing two-dimensional spindle-type chromophores was successfully prepared via the sol–gel process. After corona poling, the EO coefficient of the hybrid film was calculated to be around 12 pm/V. By anchoring the chromophores to the three-dimensional silica network by two points of attachment, the hybrid film exhibited excellent thermal stability. Acknowledgments This work was supported by the National Natural Science Foundation of China (Grant No. 20974036, 20921003), Science and Technology Development Project of Jilin Province (20090317). References [1] Kim SK, Hung YC, Seo BJ, Geary K, Yuan W, Bortnik B, et al. Appl Phys Lett 2005;87 061112-1-3. [2] Lee M, Katz HE, Erben C, Gill DM, Heber JD, Mcgee DJ, et al. Science 2002;298:1401–3. [3] Dalton LR, Steier WH, Robinson BH, Zhang C, Ren A, Garner S, et al. J Mater Chem 1999;9:1905–20. [4] Kang H, Evmenenko G, Marks TJ. J Am Chem Soc 2006;128:6194–205. [5] Liao Y, Eichinger BE, Firestone KA, Jen AK-Y, Dalton LR, Robinson BH, et al. J Am Chem Soc 2005;127:2758–66. [6] Jang SH, Luo J, Tucker NM, Leclercq A, Dalton LR, Jen AK-Y, et al. Chem Mater 2006;18:2982–8. [7] Cu YJ, Qian GD, Chen LJ, Wang ZY, Gao JK, Wang MQ. J Phys Chem B 2006;110:4105–10. [8] Wang SW, Zhao LS, Yang S, Pang SJ, Cui ZC. Mater Lett 2009;63:292–4. [9] Chen LJ, Qian GD, Jin XF, Cui YJ, Gao JK, Wang ZY, et al. J Phys Chem B 2007;111:3115–21. [10] Chen LJ, Qian GD, Cui YJ, Wang MQ. J Phys Chem B 2006;110:19176–82. [11] Yu JC, Qiu JY, Cui YJ, Hu JT, Liu LY, Qian GD, et al. Mater Lett 2009;63:2594–6. [12] Cui YJ, Li BZ, Yu C, Yu JC, Gao JK, Qian GD, et al. Thin Solid Films 2009;517:5075–8. [13] Jin XF, Cui YJ, Gao JK, Nie JJ, Qian GD. Thin Solid Films 2009;517:5079–83. [14] Zhang XL, Shi ZS, Li M, Wan Y, Zhao LS, Cui ZC, et al. Macromol Chem Phys, accepted for publication. doi:10.1002/macp.201000626. [15] Teng CC, Man HT. Appl Phys Lett 1990;56:1734–6.