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Synthesis and characterization of conjugated polymer containing azobenzene and oxadiazole units
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Chinese Chemical Letters 20 (2009) 235–237 www.elsevier.com/locate/cclet
Synthesis and characterization of conjugated polymer containing azobenzene and oxadiazole units Yue Zhang, Shi Jun Yu *, Lu Wang, Cong Li College of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian 116029, China Received 7 July 2008
Abstract A novel conjugated polymer containing azobenzene and oxadiazole units was synthesized through multi-step synthesis. The structures and properties of monomer and polymer were characterized and evaluated with IR, 1H NMR, UV, TGA and GPC, respectively. Polymer with long side chain of alkoxy shows good solubility, thermal stability and photoisomerization property. # 2008 Shi Jun Yu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Oxadiazole; Conjugated polymer; Synthesis; Characterization
A variety of conjugated polymers containing oxadiazole units have been synthesized, and their properties have been investigated [1–6]. However, most of them show poor solubility [7]. Long alkoxy side-chain was introduced to the polymer in this paper to improve the solubility [8,9]. The azobenzene chromophore with trans-cis photoisomerization and photo-induced alignment properties [10]. It is hence very interesting to synthesize conjugated polymer containing azobenzene unit. Here we report the preparation, thermal stability photoresponsive and conductivity of a novel soluble aromatic conjugated polymer containing azobenzene and oxadiazole units. 1. Experimental CHCl3 and THF were used after distillation over P2O5 and sodium, respectively. Other solvents and reagents were used directly as purchased without further purification. The IR Spectra were recorded as KBr pellets on a Bio-Rad FTS-135 spectrophotometer. The 1H NMR spectra were recorded on a Bruker AV 500-MHz spectrometer. The UV–vis absorption spectra were recorded on a Shimadzu-240 spectrophotometer. Trans–cis photoisomerizations of azobenzene units were carried out by using an Hg lamp with filters. Molecular weight and polydispersity were estimated by GPC at 40 8C using a PL-GPC220 instrument. Thermogravimetric analysis (TGA) was performed on a PerkinElmer Diamond TG/DTA under nitrogen at a heating rate of 10 8C/min. Synthesis of monomer 6 is according to Scheme 1. Compound 4 was obtained through nitrification, esterification, reduction, diazotization, coupling reaction, respectively. The synthesis of compounds 5 and 6 is similar to Ref. [11]. * Corresponding author. E-mail address: [email protected] (S.J. Yu). 1001-8417/$ – see front matter # 2008 Shi Jun Yu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2008.10.002
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Y. Zhang et al. / Chinese Chemical Letters 20 (2009) 235–237
Scheme 1. The synthesis routes of monomer and polymerization: (a) HNO3, H2SO4; (b) H2SO4, C2H5OH; (c) Pd/C, H2; (d) NaNO2/HCl, C6H5OH, NaOH; (e) Br(CH2)15CH3, K2CO3; (f) NH2NH2H2O, ethanol; (g) ClCOC6H4COCl, NMP, Et3N, LiCl; (h) POCl3.
The crude product of 6 was purified through recrystallization (DMF:H2O = 5:1) and yellow crystal product was obtained in 80.6% yield. IR (KBr, cm 1): 3316 (s, –N–H), 2920, 2852 (vs and s, C–H), 1656 (s, C O), 1602, 1500 (s, Ar), 1254, 1144 (vs and s, –C–O–C–), 834, 684 (m, Ar). 1H NMR (DMSO-d6, 500 MHz, d ppm): 10.00 (s, 2H, H10), 8.40 (s, 1H, H9), 8.37 (s, 2H, H8), 7.95 (d, 2H, H7), 7.15 (d, 2H, H6), 4.59 (br., 4H, H11), 4.07 (t, 2H, H5), 1.74 (m, 2H, H4), 1.38 (m, 2H, H3), 1.31–1.21 (m, 24H, H2), 0.83 (t, 3H, H1). Pre-polymer: 0.100 g anhydrous LiCl and 2 mL Et3N were added to 10 mL NMP containing 0.406 g (2 mmol) 1,3benzenedicarbonyl dichloride, then 1.080 g (2 mmol) compound 6 in NMP was added dropwise to above solution. The mixture was stirred at 80 8C for 3 h, cooled and poured into 100 mL methanol. The solid was collected, dried under vacuum for 24 h, yield: 82.4%. IR (KBr, cm 1): 3428 (s, –N–H), 2920, 2852 (vs and s, –(CH2)15CH3), 1656 (s, C O), 1592, 1496 (s, Ar), 1254, 1144 (vs and s, –C–O–C–), 830, 674 (m, Ar). 1H NMR (DMSO-d6, 500 MHz, d ppm): 9.80– 9.90 (br., 2H, H10), 8.60–8.64 (br., 2H, H8,9), 8.10 (br., 3H, H7,11,12), 7.18 (br., 2H, H6,13), 4.11 (br., 2H, H5), 1.77 (br., 2H, H4), 1.44 (br., 2H, H3), 1.21–1.31 (br., 24H, H2), 0.84 (t, 3H, H1). Polymer: 0.900 g pre-polymer and 15 mL POCl3 were added in a 50 mL round-bottom flask equipped with reflux condenser, heated to reflux for 8 h, cooled and poured into 100 mL ice pieces, the polymer was collected and washed with water, sodium carbonate solution, water, ethanol, respectively. The polymer was purified by dissolving in THF and precipitating in methanol, The product was dried under vacuum at 50 8C for 24 h. Yellow powder, yield: 88.1%. GPC: Mw = 8501, Mw/Mn = 1.55. IR (KBr, cm 1): 2924, 2852 (vs and s, C–H) 1600, 1500 (s, Ar), 1544 (m, C N), 1254, 1140 (vs and s, –C–O–C–), 836, 678 (m, Ar). 1H NMR (CDCl3-d6, 500 MHz, d ppm): 8.65 (br., 2H, H7,8), 7.98(br., 3H, H6,9,10), 7.02 (br., 2H, H5,11), 4.05 (br., 2H, H4), 1.84 (br., 2H, H3), 1.15–1.45 (br., 26H, H2), 0.88 (br., 3H, H1). 2. Results and discussion The polymer with long side chain of alkoxy in this article is soluble in common organic solvents such as CHCl3, THF, toluene and dioxane, improving the solubility of general conjugated polymer containing oxadiazole. The electrical conductivity of polymer is 3.2 10 1 s/m. Molecular weight is 8501 g/mol, PD is 1.55. The infrared spectra of polymer exhibits a characteristic absorption of oxadiazole at 1544 cm 1. The electronic absorption spectra of polymer (1.2 10 5 g/mL) shows a strong absorption peak locating at 306 nm, corresponding the p–p* transition of oxadiazole chromophores. Compared with the 1H NMR spectrum of per-polymer, the broad
Y. Zhang et al. / Chinese Chemical Letters 20 (2009) 235–237
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Fig. 1. The trans–cis photoisomerizations of azobenzene unit of monomer and polymer under 365 nm UV radiation: (a) monomer; (b) polymer.
absorption band at 9.8–9.9 corresponding to –HNNH– disappears in the polymer spectrum. The monomer has conversed to polymer. The TGA thermogram of polymer shows a significant weight loss at 290 8C, it is attributed to the damage of structure of azo. It can be seen that the thermal stability of azo functional group is low in conjugate structure of polymer. Fig. 1 is the trans–cis photoisomerizations of azobenzene units of monomer and polymer under 365 nm UV radiation. It can be seen that p–p* transition absorption peaks decreased while n–p* transition absorption peaks increased with irradiation time increasing. The photostationary state was obtained after irradiation for 7 min and 6 min respectively and the maximum absorption wavelength of p–p* transitions present blue-shift at the same time. This is due to the contents of trans-isomer of azobenzene structure decreased while the other increased with irradiation time increasing, the degree of conjugate decreased. The efficiency of trans-cisphotoisomerization (R) and the contents of cis-isomer (Y) of monomer and polymer were calculated [12]. R are 83.2%, 69.2%, respectively. Y are 87.3%, 72.6%, respectively. The R and Y of monomer are greater than polymer, which are attributed to the increased steric hindrance in polymer. In conclusion, we successfully synthesized a conjugated polymer containing azobenzene and oxadiazole units. Polymer with long side chain of alkoxy shows good solubility, photo absorption properties and conductive property, expected to be applied in the fields of optics, electron-transport and electroluminescence material. Acknowledgment This work was supported by the National Natural Science Foundation of China (No. 20573049). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]
J.A. Mikroyannidis, Synth. Met. 145 (2004) 271. B.B. Xu, Y.C. Pan, J.H. Zhang, et al. Synth. Met. 114 (2000) 337. J.H. Kim, H. Lee, Synth. Met. 143 (2004) 13. S.Y. Zhang, Fan Kong, R. Sun, et al. J. Appl. Polym. Sci. 89 (2003) 2618. D.C. Shin, J.H. Ahn, Y.H. Kim, et al. J. Polym. Sci. Part A: Polym. Chem. 38 (2000) 3086. X.R. Cai, H. Chen, T. Zhang, X. Xu, Y. Li, Q. Jiang, Chin. Chem. Lett. 18 (2007) 1342. X.C. Li, G.C.W. Spencer, A.B. Holmes, et al. Synth. Met. 76 (1996) 153. M.R. Huang, X.G. Li, W. Duan, Polym. Int. 54 (2005) 70. X.G. Li, W. Duan, M.R. Huang, Y.L. Yang, D.Y. Zhao, Polymer 44 (2003) 6273. D. Acierno, E. Amendola, V. Bugatti, Macromolecules 37 (2004) 6418. H. Meng, W.L. Yu, W. Huang, Macromolecules 32 (1999) 8841. J.G. Victor, J.M. Torkelson, Macromolecules 20 (1987) 2241.
Chinese Chemical Letters 20 (2009) 235–237 www.elsevier.com/locate/cclet
Synthesis and characterization of conjugated polymer containing azobenzene and oxadiazole units Yue Zhang, Shi Jun Yu *, Lu Wang, Cong Li College of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian 116029, China Received 7 July 2008
Abstract A novel conjugated polymer containing azobenzene and oxadiazole units was synthesized through multi-step synthesis. The structures and properties of monomer and polymer were characterized and evaluated with IR, 1H NMR, UV, TGA and GPC, respectively. Polymer with long side chain of alkoxy shows good solubility, thermal stability and photoisomerization property. # 2008 Shi Jun Yu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Oxadiazole; Conjugated polymer; Synthesis; Characterization
A variety of conjugated polymers containing oxadiazole units have been synthesized, and their properties have been investigated [1–6]. However, most of them show poor solubility [7]. Long alkoxy side-chain was introduced to the polymer in this paper to improve the solubility [8,9]. The azobenzene chromophore with trans-cis photoisomerization and photo-induced alignment properties [10]. It is hence very interesting to synthesize conjugated polymer containing azobenzene unit. Here we report the preparation, thermal stability photoresponsive and conductivity of a novel soluble aromatic conjugated polymer containing azobenzene and oxadiazole units. 1. Experimental CHCl3 and THF were used after distillation over P2O5 and sodium, respectively. Other solvents and reagents were used directly as purchased without further purification. The IR Spectra were recorded as KBr pellets on a Bio-Rad FTS-135 spectrophotometer. The 1H NMR spectra were recorded on a Bruker AV 500-MHz spectrometer. The UV–vis absorption spectra were recorded on a Shimadzu-240 spectrophotometer. Trans–cis photoisomerizations of azobenzene units were carried out by using an Hg lamp with filters. Molecular weight and polydispersity were estimated by GPC at 40 8C using a PL-GPC220 instrument. Thermogravimetric analysis (TGA) was performed on a PerkinElmer Diamond TG/DTA under nitrogen at a heating rate of 10 8C/min. Synthesis of monomer 6 is according to Scheme 1. Compound 4 was obtained through nitrification, esterification, reduction, diazotization, coupling reaction, respectively. The synthesis of compounds 5 and 6 is similar to Ref. [11]. * Corresponding author. E-mail address: [email protected] (S.J. Yu). 1001-8417/$ – see front matter # 2008 Shi Jun Yu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2008.10.002
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Y. Zhang et al. / Chinese Chemical Letters 20 (2009) 235–237
Scheme 1. The synthesis routes of monomer and polymerization: (a) HNO3, H2SO4; (b) H2SO4, C2H5OH; (c) Pd/C, H2; (d) NaNO2/HCl, C6H5OH, NaOH; (e) Br(CH2)15CH3, K2CO3; (f) NH2NH2H2O, ethanol; (g) ClCOC6H4COCl, NMP, Et3N, LiCl; (h) POCl3.
The crude product of 6 was purified through recrystallization (DMF:H2O = 5:1) and yellow crystal product was obtained in 80.6% yield. IR (KBr, cm 1): 3316 (s, –N–H), 2920, 2852 (vs and s, C–H), 1656 (s, C O), 1602, 1500 (s, Ar), 1254, 1144 (vs and s, –C–O–C–), 834, 684 (m, Ar). 1H NMR (DMSO-d6, 500 MHz, d ppm): 10.00 (s, 2H, H10), 8.40 (s, 1H, H9), 8.37 (s, 2H, H8), 7.95 (d, 2H, H7), 7.15 (d, 2H, H6), 4.59 (br., 4H, H11), 4.07 (t, 2H, H5), 1.74 (m, 2H, H4), 1.38 (m, 2H, H3), 1.31–1.21 (m, 24H, H2), 0.83 (t, 3H, H1). Pre-polymer: 0.100 g anhydrous LiCl and 2 mL Et3N were added to 10 mL NMP containing 0.406 g (2 mmol) 1,3benzenedicarbonyl dichloride, then 1.080 g (2 mmol) compound 6 in NMP was added dropwise to above solution. The mixture was stirred at 80 8C for 3 h, cooled and poured into 100 mL methanol. The solid was collected, dried under vacuum for 24 h, yield: 82.4%. IR (KBr, cm 1): 3428 (s, –N–H), 2920, 2852 (vs and s, –(CH2)15CH3), 1656 (s, C O), 1592, 1496 (s, Ar), 1254, 1144 (vs and s, –C–O–C–), 830, 674 (m, Ar). 1H NMR (DMSO-d6, 500 MHz, d ppm): 9.80– 9.90 (br., 2H, H10), 8.60–8.64 (br., 2H, H8,9), 8.10 (br., 3H, H7,11,12), 7.18 (br., 2H, H6,13), 4.11 (br., 2H, H5), 1.77 (br., 2H, H4), 1.44 (br., 2H, H3), 1.21–1.31 (br., 24H, H2), 0.84 (t, 3H, H1). Polymer: 0.900 g pre-polymer and 15 mL POCl3 were added in a 50 mL round-bottom flask equipped with reflux condenser, heated to reflux for 8 h, cooled and poured into 100 mL ice pieces, the polymer was collected and washed with water, sodium carbonate solution, water, ethanol, respectively. The polymer was purified by dissolving in THF and precipitating in methanol, The product was dried under vacuum at 50 8C for 24 h. Yellow powder, yield: 88.1%. GPC: Mw = 8501, Mw/Mn = 1.55. IR (KBr, cm 1): 2924, 2852 (vs and s, C–H) 1600, 1500 (s, Ar), 1544 (m, C N), 1254, 1140 (vs and s, –C–O–C–), 836, 678 (m, Ar). 1H NMR (CDCl3-d6, 500 MHz, d ppm): 8.65 (br., 2H, H7,8), 7.98(br., 3H, H6,9,10), 7.02 (br., 2H, H5,11), 4.05 (br., 2H, H4), 1.84 (br., 2H, H3), 1.15–1.45 (br., 26H, H2), 0.88 (br., 3H, H1). 2. Results and discussion The polymer with long side chain of alkoxy in this article is soluble in common organic solvents such as CHCl3, THF, toluene and dioxane, improving the solubility of general conjugated polymer containing oxadiazole. The electrical conductivity of polymer is 3.2 10 1 s/m. Molecular weight is 8501 g/mol, PD is 1.55. The infrared spectra of polymer exhibits a characteristic absorption of oxadiazole at 1544 cm 1. The electronic absorption spectra of polymer (1.2 10 5 g/mL) shows a strong absorption peak locating at 306 nm, corresponding the p–p* transition of oxadiazole chromophores. Compared with the 1H NMR spectrum of per-polymer, the broad
Y. Zhang et al. / Chinese Chemical Letters 20 (2009) 235–237
237
Fig. 1. The trans–cis photoisomerizations of azobenzene unit of monomer and polymer under 365 nm UV radiation: (a) monomer; (b) polymer.
absorption band at 9.8–9.9 corresponding to –HNNH– disappears in the polymer spectrum. The monomer has conversed to polymer. The TGA thermogram of polymer shows a significant weight loss at 290 8C, it is attributed to the damage of structure of azo. It can be seen that the thermal stability of azo functional group is low in conjugate structure of polymer. Fig. 1 is the trans–cis photoisomerizations of azobenzene units of monomer and polymer under 365 nm UV radiation. It can be seen that p–p* transition absorption peaks decreased while n–p* transition absorption peaks increased with irradiation time increasing. The photostationary state was obtained after irradiation for 7 min and 6 min respectively and the maximum absorption wavelength of p–p* transitions present blue-shift at the same time. This is due to the contents of trans-isomer of azobenzene structure decreased while the other increased with irradiation time increasing, the degree of conjugate decreased. The efficiency of trans-cisphotoisomerization (R) and the contents of cis-isomer (Y) of monomer and polymer were calculated [12]. R are 83.2%, 69.2%, respectively. Y are 87.3%, 72.6%, respectively. The R and Y of monomer are greater than polymer, which are attributed to the increased steric hindrance in polymer. In conclusion, we successfully synthesized a conjugated polymer containing azobenzene and oxadiazole units. Polymer with long side chain of alkoxy shows good solubility, photo absorption properties and conductive property, expected to be applied in the fields of optics, electron-transport and electroluminescence material. Acknowledgment This work was supported by the National Natural Science Foundation of China (No. 20573049). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]
J.A. Mikroyannidis, Synth. Met. 145 (2004) 271. B.B. Xu, Y.C. Pan, J.H. Zhang, et al. Synth. Met. 114 (2000) 337. J.H. Kim, H. Lee, Synth. Met. 143 (2004) 13. S.Y. Zhang, Fan Kong, R. Sun, et al. J. Appl. Polym. Sci. 89 (2003) 2618. D.C. Shin, J.H. Ahn, Y.H. Kim, et al. J. Polym. Sci. Part A: Polym. Chem. 38 (2000) 3086. X.R. Cai, H. Chen, T. Zhang, X. Xu, Y. Li, Q. Jiang, Chin. Chem. Lett. 18 (2007) 1342. X.C. Li, G.C.W. Spencer, A.B. Holmes, et al. Synth. Met. 76 (1996) 153. M.R. Huang, X.G. Li, W. Duan, Polym. Int. 54 (2005) 70. X.G. Li, W. Duan, M.R. Huang, Y.L. Yang, D.Y. Zhao, Polymer 44 (2003) 6273. D. Acierno, E. Amendola, V. Bugatti, Macromolecules 37 (2004) 6418. H. Meng, W.L. Yu, W. Huang, Macromolecules 32 (1999) 8841. J.G. Victor, J.M. Torkelson, Macromolecules 20 (1987) 2241.