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Synthesis of self-doped conducting polyaniline bearing phosphonic acid
Accepted Manuscript Synthesis of self-doped conducting polyaniline bearing phosphonic acid Toru Amaya, Yasushi Abe, Yuhi Inada, Toshikazu Hirao PII: DOI: Reference:
S0040-4039(14)00752-7 http://dx.doi.org/10.1016/j.tetlet.2014.04.115 TETL 44577
To appear in:
Tetrahedron Letters
Received Date: Revised Date: Accepted Date:
10 March 2014 22 April 2014 30 April 2014
Please cite this article as: Amaya, T., Abe, Y., Inada, Y., Hirao, T., Synthesis of self-doped conducting polyaniline bearing phosphonic acid, Tetrahedron Letters (2014), doi: http://dx.doi.org/10.1016/j.tetlet.2014.04.115
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Synthesis of self-doped conducting polyaniline bearing phosphonic acid Toru Amaya, Yasushi Abe, Yuhi Inada, Toshikazu Hirao
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1
Tetrahedron Letters journal homepage: www.elsevier.com
Synthesis of self-doped conducting polyaniline bearing phosphonic acid Toru Amayaa,*, Yasushi Abea,b, Yuhi Inadaa, Toshikazu Hiraoa,* a
Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Yamada-oka, Suita, Osaka 565-0871, Japan Osaka R&D Laboratory, Daihachi Chemical Industry Co.,LTD., 3-5-7 Chodo, Higashiosaka, Osaka 577-0056, Japan
b
ARTICLE INFO
ABSTRACT
Article history: Received Received in revised form Accepted Available online
As a self-doped conducting polyaniline bearing phosphonic acid, poly(2-methoxyaniline-5phosphonic acid) (PMAP) was synthesized via oxidative polymerization of 2-methoxyaniline-5phosphonic acid. The pyridinium salt of thus-obtained PMAP was water-soluble and its film exhibited conductivity. 2009 Elsevier Ltd. All rights reserved.
Keywords: Conducting polymer Polyaniline Phosphonic acid Self-doping Water-soluble
1 2 3 4 5 6 7 8 9 10 11
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Conducting polymers have attracted considerable interest due to their wide application for polymer-based electronics and biosensors.1 To exhibit their conductivity, the charge carriers must become mobile in the polymer chain. Therefore, the partial oxidation or reduction of intrinsically conducting -conjugated polymer is usually required to form the conductive state, and this process is called doping.2 In contrast to such redox-mediating doping, polyaniline (emeraldine base) can be doped by simple protonation to lead to conductive polysemiquinone radical cationic (polaronic) state via reorganization of the electronic structure (Figure 1a).3 Organic conducting polymers that contain covalently bound, charged, functional groups that impact the properties of the polymer are referred to as self-doped conducting polymers.4 A covalently attached acid group to the polyaniline backbone can dope itself without an external dopant. As such self-doped conducting polyanilines, sulfonated polyaniline was demonstrated by Epstein et al. in 1990.5 On the other hand, there is a great demand for highly water-soluble conducting polymers, particularly in applications with processing using aqueous solution or operated in biological environments.6 From this point of view, self-doped polyaniline possessing a hydrophilic group is also attractive. In our previous study, we have developed the hybrid systems consisted of poly(2-methoxyaniline-5-sulfonic acid) and transition metals,7 and reported their catalytic application for the oxidation reaction in aqueous solution. 7c-f Despite such attractive features for self-doped polyaniline, development of self-doped polyanilines is still limited, especially most of them have a quite low electrical conductivity.8 Concerning the synthesis, there are mainly two strategies to introduce an acid group. One is post-synthetic modifications of polyaniline. The other is the polymerization of monomer
33 34
35 36 37 38 39 40
possessing acid group. The latter should make the polymer design more flexible. In the present study, we chose polyaniline phosphonic acid 1 as a synthetic target (Figure 1b). Differing from sulfonic acid, two acidic protons are available in phosphonic acid. This feature would provide a base resistance property or further acid/base complexation. Alkylphosphonic acid is known to have an enough acidity to dope the polyaniline (emeraldine base).9 So far, self-
Figure 1. (a) Doping of polyaniline (emeraldine base). (b)
Polyaniline phosphonic acid 1.
2
Tetrahedron
doped polyaniline with phosphonic acid attached to the backbone through methylene unit was synthesized.8g,h In our designed polyaniline phosphonic acid, a directly attached acid group to the backbone is expected to show more efficient selfdoping. Herein, we describe the synthesis of poly(2methoxyaniline-5-phosphonic acid) (PMAP, 1b) via oxidative polymerization of 2-methoxyaniline-5-phosphonic acid. The pyridinium salt of thus-obtained PMAP was water-soluble and its film exhibited conductivity.
41 42 43 44 45 46 47 48 49
50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72
73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88
89 90 91 92 93
94 95 96 97 98 99 100 101 102 103 104
To synthesize 1a, oxidative polymerization of the monomer 2a10a or 2b10b was investigated using (NH4)2S2O8 as an oxidant (Scheme 1a). However, the reaction conditions to afford the conducting polymers were not found from both monomers despite several attempts of the conditions. To improve the reactivity for polymerization, monomer 6 possessing methoxy group was designed. The synthetic scheme for 6 is shown in Scheme 1b. Our developed Pd-catalysed coupling reaction was employed to introduce phosphonate group. 11 Commercially available bromide 3 was coupled with HPO(OEt)2 in the presence of Pd(OAc)2 (10mol%) to give diethylphosphonate 4 in 69% yield. Hydrogenation of nitro group followed by acid-catalysed hydrolysis gave the monomer 6 (2 steps 72% yield). The thusobtained monomer 6 was polymerized with (NH4)2S2O8 in 2.5 M aqueous pyridine solution at -5 °C for 5 days (Scheme 1c). After the treatment with 1 M aqueous HCl solution, the polymer 1b was obtained in 53% yield as a black solid. The obtained polymer 1b has a weight average molecular weight (Mw) of 2000 and a polydispersity index of 2.7, which were determined by GPC analysis (see Figure S1 in Supplementary Material). Although PMAP 1b did not exhibit a good solubility in an acidic to neutral aqueous solution, it was soluble in a basic aqueous solution. The pyridinium salt of PMAP 1b was also soluble in neutral water.
Scheme 1. (a) Polymerization of 2. (b) Synthesis of monomer 6. (c) Synthesis of PMAP 1b.
Figure 2 shows UV-vis-NIR spectra for 1b. Aqueous solution of the PMAP/pyridine complex (molar ratio = 1:1 based on the monomer unit) exhibited pH 5.35, and its color was brown. This complex has a maximum absorption at 281 and a shoulder peak around 420 nm. The shoulder peak around 420 nm should be attributed to a polaron band.12 Steadily increasing absorption starting from around 1000 nm was also observed (free carrier tail). Such free carrier tail is characteristic of doped conducting polyanilines.12 On the other hand, the pH 8.98 aqueous solution of the PMAP/pyridine complex (molar ratio = 1:1 based on the monomer unit) has maximum absorptions at 283 and 683 nm, and a shoulder peak was observed around 430 nm. The broad absorption around 680 nm should be assigned as a further localized polaron band.12 It is worth noting that the absorption from around 1000 nm was also found in the weakly basic solution.
Figure 2. UV-vis-NIR spectra for PMAP 1b at 298 K (4.9 x 10-4 M based on the monomer unit): PMAP/pyridine (1:1) in H2O (pH 5.35) (solid line) and in the pH 8.98 aqueous solution (dashed line).
ESR spectrum of the aqueous solution of the PMAP/pyridine complex (molar ratio = 1:2 based on the monomer unit) showed a single resonance line centered on around g = 2.0036 without hyperfine coupling in water (Figure 3). This is characteristic of delocalized free radicals.13 The electrical resistance of the polymer film was measured by the direct-current (DC) method (Table 1). The film was formed by drop-casting the aqueous 1% (w/w) suspension or solution of the pyridinium salt of PMAP 1b on a glass substrate, on which a pair of indium tin oxide (ITO) electrodes with a gap (width: 200 m, height: 150 nm, see the figure in Table 1) were placed. An aqueous suspension and solutions of PMAP 1b were prepared with changing the molar ratio of pyridine to the PMAP 1b. Addition of two molar equivalents of pyridine based on the monomer unit was required to prepare 1% (w/w) PMAP 1b solution in water. The electrical resistances of the film for the
Figure 3. ESR spectrum for PMAP/pyridine (1:2) in H2O at 298 K (4.9 x 10-2 M based on the monomer unit). 105 106 107
pyridinium salts of PMAP were ranged from 14 to k, which corresponds to 0.19 to 0.13 S/cm in terms of conductivity (Table 1, entries 1-3). The sheet resistance of the drop-cast film was
3 108 109 110 111 112 113 114 115 116 117 118 119
120 121 122
measured by a four-point probe method. The film was formed by drop-casting the aqueous 2% (w/w) solution of the pyridinium salt of PMAP 1b (molar ratio = 1:2 based on the monomer unit) on a glass substrate. The sheet resistance was 3.8 x 106 /□. The spin-coating film was also formed with the aqueous 2% (w/w) solution of the pyridinium salt of PMAP 1b (molar ratio = 1:2 based on the monomer unit) on a glass substrate. The photo of the film was shown in Figure 4. It was a transparent light brown film. The thickness was 18 nm. The scanning electron microscopy (SEM) images of the spin-coating film were shown in Figure S3 in Supplementary Material. The uniformly formed surface of the film was observed. Table 1. Electrical resistance and conductivity for the drop-cast films of the aqueous 1% (w/w) suspension or solution of the pyridinium salts of PMAP 1b
147
University for the conductivity measurements by the four-point probe method, and Dr. H. Yamamoto and Prof. T. Kozawa at Osaka University for the film thickness measurements. We also thank Comprehensive Analysis Center of the Institute of Scientific and Industrial Research, Osaka University for the ICPMS measurements and SEM analysis.
148
Supplementary Material
142 143 144 145 146
150
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/ .
151
References and notes
149
152
1.
153
Entry 1 2 3 123 124 125
Molar equivalents of pyridinea 1 2 4
Suspension or solution Suspension Solution Solution
Electrical resistance (k) 14 20 20
Conductivity (S/cm)b 0.19 0.13 0.13
a
Based on the monomer unit. bConductivity was calculated on the assumption that the gap (see the below figure) was filled with the polymer. Therefore, the obtained value is the minimum value.
154 155
2. 3.
156 157
4.
158 159 160 161 162 163
5. 6.
164 165 166
7.
167 168 169 126
170 171
127
172 128
173 174
8.
175 176 177 178 179 180 181 182 183 184 185 186 187 129
188
Figure 4. Photo of the spin-coating film formed with the aqueous 2% (w/w) solution of the pyridinium salt of PMAP 1b (molar ratio = 1:2 based on the monomer unit) on a glass substrate (26 x 26 mm) and its thickness.
189 190 191 192 193 194
130 195 131 132 133 134 135 136 137 138
139
140 141
In conclusion, the self-doped conducting polyaniline PMAP 1b was successfully synthesized via oxidative polymerization. This is the first synthesis of the polyaniline bearing phosphonic acid directly attached to the backbone. Self-doping of PMAP 1b was clearly shown by UV-vis-NIR and ESR measurements. The pyridinium salt of PMAP 1b was water-soluble and its film exhibited conductivity. The electrical materials application of PMAP is now underway. Acknowledgments We thank Dr. T. Suenobu and Prof. S. Fukuzumi at Osaka University for the ESR measurements, Dr. R. Tsuji at Osaka
9.
196 197
10.
198 199 200 201 202
11.
203 204 205
12.
206 207 208
13.
Skotheim, T. A.; Reynolds, J. R. Conjugated Polymers: Theory, Synthesis, Properties, and Characterization, CRC: 2007. MacDiarmid, A. G. Angew. Chem. Int. Ed. 2001, 40, 2581-2590. Epstein, A. J.; MacDiarmid, A. G. Mol. Cryst. Liq. Cryst. 1988, 160, 165-173. (a) Patil, A. O.; Ikenoue, Y.; Wudl, F.; Heeger, A. J. J. Am. Chem. Soc. 1987, 109, 1858-1859. (b) Patil, A. O.; Ikenoue, Y.; Basescu, N.; Colaneri, N.; Chen, J.; Wudl, F.; Heeger, A. J. Synth. Met. 1987, 20, 151-159. (c) Freund, M. S.; Deore, B. Self-Doped Conducting Polymers, John Wiley & Sons, Ltd.: New York, 2007. Yue, J.; Epstein, A. J. J. Am. Chem. Soc. 1990, 112, 2800-2801. (a) Lim, J.-H.; Mirkin, C. A. Adv. Mater. 2002, 14, 1474-1477. (b) Jiang, H.; Taranekar, P.; Reynolds, J. R.; Schanze, K. S. Angew. Chem. Int. Ed. 2009, 48, 4300-4316. (a) Amaya, T.; Koga, S.; Hirao, T. Tetrahedron Lett. 2009, 50, 1032-1034. (b) Amaya, T.; Saio, D.; Koga, S.; Hirao, T. Macromolecules 2010, 43, 1175-1177. (c) Saio, D.; Amaya, T.; Hirao, T. Adv. Synth. Catal. 2010, 352, 2177-2182. (d) Amaya, T.; Ito, T.; Inada, Y.; Saio, D.; Hirao, T. Tetrahedron Lett. 2012, 53, 6144-6147. (e) Amaya, T.; Ito, T.; Hirao, T. Heterocycles, 2012, 86, 927-932. (f) Amaya, T.; Ito, T.; Hirao, T. Tetrahedron Lett. 2013, 54, 2409-2411. (a) Hany, P.; Geniès, E. M.; Santier, C. Synth. Met. 1989, 31, 369378. (b) Bergeron, J.-Y.; Chevalier, J.-W.; Dao, L. H. J. Chem. Soc., Chem. Commun. 1990, 180-181. (c) Yue, J.; Gordon, G.; Epstein, A. J. Polymer 1992, 33, 4410-4418. (d) Chan, H. S. O.; Ng, S. C.; Sim, A. S.; Tan, K. L.; Tan, B. T. G. Macromolecules 1992, 25, 6029-6034. (e) DeArmitt, C.; Armes, S. P.; Winter, J.; Uribe, F. A.; Gottesfeld, S.; Mombourquette, C. Polymer 1993, 34, 158-162. (f) Nguyen, M. T.; Kasai, P.; Miller, J. L.; Diaz, A. F. Macromolecules 1994, 27, 3625-3631. (g) Ng, S. C.; Chan, H. S. O.; Huang, H. H.; Ho, P. K. H. J. Chem. Soc., Chem. Commun. 1995, 1327-1328. (h) Chan, H. S. O.; Ho, P. K. H.; Ng, S. C.; Tan, B. T. G.; Tan, K. L. J. Am. Chem. Soc. 1995, 117, 8517-8523. (i) Shimizu, S.; Saitoh, T.; Uzawa, M.; Yuasa, M.; Yano, K.; Maruyama, T.; Watanabe, K. Synth. Met. 1997, 85, 1337-1338. (j) Nicolas, M.; Fabre, B.; Marchand, G.; Simonet, J. Eur. J. Org. Chem. 2000, 1703-1710. (k) Shoji, E.; Freund, M. S. J. Am. Chem. Soc. 2001, 123, 3383-3384. (l) Ohno, N.; Wang, H.-J.; Yan, H.; Toshima, N. Polym. J. 2001, 33, 165-171. (m) Han, C.-C.; Lu, C.H.; Hong, S.-P.; Yang, K.-F.; Macromolecules 2003, 36, 79087915. (n) For a review: Malinauskas, A. J. Power Sources 2004, 126, 214-220. Chan, H. S. O.; Ng, S. C.; Ho, P. K. H. Macromolecules 1994, 27, 2159-2164. Preparation: (a) Cooper, R. J.; Camp, P. J.; Gordon, R. J.; Henderson, D. K.; Henry, D. C. R.; McNab, H.; De Silva, S. S.; Tackley, D.; Tasker, P. A.; Wight, P. Dalton Trans. 2006, 27852793. (b) Mucha, A.; Kunert, A.; Grembecka, J.; Pawełczak, M.; Kafarski, P. Eur. J. Med. Chem. 2006, 41, 768-772. (a) Hirao, T.; Matsunaga, T.; Ohshiro, Y.; Agawa, T. Synthesis 1981, 56-57. (b) Hirao, T.; Matsunaga, T.; Yamada, N.; Ohshiro, Y.; Agawa, T. Bull. Chem. Soc. Jpn. 1982, 55, 909-913. Xia, Y.; Wiesinger, J. M.; MacDiarmid, A. G. Chem. Mater. 1995, 7, 443-445. Dennany, L.; Innis, P. C.; Masdarolomoor, F.; Wallace, G. G. J. Phys. Chem. B 2010, 114, 2337-2341.
S0040-4039(14)00752-7 http://dx.doi.org/10.1016/j.tetlet.2014.04.115 TETL 44577
To appear in:
Tetrahedron Letters
Received Date: Revised Date: Accepted Date:
10 March 2014 22 April 2014 30 April 2014
Please cite this article as: Amaya, T., Abe, Y., Inada, Y., Hirao, T., Synthesis of self-doped conducting polyaniline bearing phosphonic acid, Tetrahedron Letters (2014), doi: http://dx.doi.org/10.1016/j.tetlet.2014.04.115
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Graphical Abstract To create your abstract, type over the instructions in the template box below. Fonts or abstract dimensions should not be changed or altered.
Synthesis of self-doped conducting polyaniline bearing phosphonic acid Toru Amaya, Yasushi Abe, Yuhi Inada, Toshikazu Hirao
Leave this area blank for abstract info.
1
Tetrahedron Letters journal homepage: www.elsevier.com
Synthesis of self-doped conducting polyaniline bearing phosphonic acid Toru Amayaa,*, Yasushi Abea,b, Yuhi Inadaa, Toshikazu Hiraoa,* a
Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Yamada-oka, Suita, Osaka 565-0871, Japan Osaka R&D Laboratory, Daihachi Chemical Industry Co.,LTD., 3-5-7 Chodo, Higashiosaka, Osaka 577-0056, Japan
b
ARTICLE INFO
ABSTRACT
Article history: Received Received in revised form Accepted Available online
As a self-doped conducting polyaniline bearing phosphonic acid, poly(2-methoxyaniline-5phosphonic acid) (PMAP) was synthesized via oxidative polymerization of 2-methoxyaniline-5phosphonic acid. The pyridinium salt of thus-obtained PMAP was water-soluble and its film exhibited conductivity. 2009 Elsevier Ltd. All rights reserved.
Keywords: Conducting polymer Polyaniline Phosphonic acid Self-doping Water-soluble
1 2 3 4 5 6 7 8 9 10 11
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Conducting polymers have attracted considerable interest due to their wide application for polymer-based electronics and biosensors.1 To exhibit their conductivity, the charge carriers must become mobile in the polymer chain. Therefore, the partial oxidation or reduction of intrinsically conducting -conjugated polymer is usually required to form the conductive state, and this process is called doping.2 In contrast to such redox-mediating doping, polyaniline (emeraldine base) can be doped by simple protonation to lead to conductive polysemiquinone radical cationic (polaronic) state via reorganization of the electronic structure (Figure 1a).3 Organic conducting polymers that contain covalently bound, charged, functional groups that impact the properties of the polymer are referred to as self-doped conducting polymers.4 A covalently attached acid group to the polyaniline backbone can dope itself without an external dopant. As such self-doped conducting polyanilines, sulfonated polyaniline was demonstrated by Epstein et al. in 1990.5 On the other hand, there is a great demand for highly water-soluble conducting polymers, particularly in applications with processing using aqueous solution or operated in biological environments.6 From this point of view, self-doped polyaniline possessing a hydrophilic group is also attractive. In our previous study, we have developed the hybrid systems consisted of poly(2-methoxyaniline-5-sulfonic acid) and transition metals,7 and reported their catalytic application for the oxidation reaction in aqueous solution. 7c-f Despite such attractive features for self-doped polyaniline, development of self-doped polyanilines is still limited, especially most of them have a quite low electrical conductivity.8 Concerning the synthesis, there are mainly two strategies to introduce an acid group. One is post-synthetic modifications of polyaniline. The other is the polymerization of monomer
33 34
35 36 37 38 39 40
possessing acid group. The latter should make the polymer design more flexible. In the present study, we chose polyaniline phosphonic acid 1 as a synthetic target (Figure 1b). Differing from sulfonic acid, two acidic protons are available in phosphonic acid. This feature would provide a base resistance property or further acid/base complexation. Alkylphosphonic acid is known to have an enough acidity to dope the polyaniline (emeraldine base).9 So far, self-
Figure 1. (a) Doping of polyaniline (emeraldine base). (b)
Polyaniline phosphonic acid 1.
2
Tetrahedron
doped polyaniline with phosphonic acid attached to the backbone through methylene unit was synthesized.8g,h In our designed polyaniline phosphonic acid, a directly attached acid group to the backbone is expected to show more efficient selfdoping. Herein, we describe the synthesis of poly(2methoxyaniline-5-phosphonic acid) (PMAP, 1b) via oxidative polymerization of 2-methoxyaniline-5-phosphonic acid. The pyridinium salt of thus-obtained PMAP was water-soluble and its film exhibited conductivity.
41 42 43 44 45 46 47 48 49
50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72
73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88
89 90 91 92 93
94 95 96 97 98 99 100 101 102 103 104
To synthesize 1a, oxidative polymerization of the monomer 2a10a or 2b10b was investigated using (NH4)2S2O8 as an oxidant (Scheme 1a). However, the reaction conditions to afford the conducting polymers were not found from both monomers despite several attempts of the conditions. To improve the reactivity for polymerization, monomer 6 possessing methoxy group was designed. The synthetic scheme for 6 is shown in Scheme 1b. Our developed Pd-catalysed coupling reaction was employed to introduce phosphonate group. 11 Commercially available bromide 3 was coupled with HPO(OEt)2 in the presence of Pd(OAc)2 (10mol%) to give diethylphosphonate 4 in 69% yield. Hydrogenation of nitro group followed by acid-catalysed hydrolysis gave the monomer 6 (2 steps 72% yield). The thusobtained monomer 6 was polymerized with (NH4)2S2O8 in 2.5 M aqueous pyridine solution at -5 °C for 5 days (Scheme 1c). After the treatment with 1 M aqueous HCl solution, the polymer 1b was obtained in 53% yield as a black solid. The obtained polymer 1b has a weight average molecular weight (Mw) of 2000 and a polydispersity index of 2.7, which were determined by GPC analysis (see Figure S1 in Supplementary Material). Although PMAP 1b did not exhibit a good solubility in an acidic to neutral aqueous solution, it was soluble in a basic aqueous solution. The pyridinium salt of PMAP 1b was also soluble in neutral water.
Scheme 1. (a) Polymerization of 2. (b) Synthesis of monomer 6. (c) Synthesis of PMAP 1b.
Figure 2 shows UV-vis-NIR spectra for 1b. Aqueous solution of the PMAP/pyridine complex (molar ratio = 1:1 based on the monomer unit) exhibited pH 5.35, and its color was brown. This complex has a maximum absorption at 281 and a shoulder peak around 420 nm. The shoulder peak around 420 nm should be attributed to a polaron band.12 Steadily increasing absorption starting from around 1000 nm was also observed (free carrier tail). Such free carrier tail is characteristic of doped conducting polyanilines.12 On the other hand, the pH 8.98 aqueous solution of the PMAP/pyridine complex (molar ratio = 1:1 based on the monomer unit) has maximum absorptions at 283 and 683 nm, and a shoulder peak was observed around 430 nm. The broad absorption around 680 nm should be assigned as a further localized polaron band.12 It is worth noting that the absorption from around 1000 nm was also found in the weakly basic solution.
Figure 2. UV-vis-NIR spectra for PMAP 1b at 298 K (4.9 x 10-4 M based on the monomer unit): PMAP/pyridine (1:1) in H2O (pH 5.35) (solid line) and in the pH 8.98 aqueous solution (dashed line).
ESR spectrum of the aqueous solution of the PMAP/pyridine complex (molar ratio = 1:2 based on the monomer unit) showed a single resonance line centered on around g = 2.0036 without hyperfine coupling in water (Figure 3). This is characteristic of delocalized free radicals.13 The electrical resistance of the polymer film was measured by the direct-current (DC) method (Table 1). The film was formed by drop-casting the aqueous 1% (w/w) suspension or solution of the pyridinium salt of PMAP 1b on a glass substrate, on which a pair of indium tin oxide (ITO) electrodes with a gap (width: 200 m, height: 150 nm, see the figure in Table 1) were placed. An aqueous suspension and solutions of PMAP 1b were prepared with changing the molar ratio of pyridine to the PMAP 1b. Addition of two molar equivalents of pyridine based on the monomer unit was required to prepare 1% (w/w) PMAP 1b solution in water. The electrical resistances of the film for the
Figure 3. ESR spectrum for PMAP/pyridine (1:2) in H2O at 298 K (4.9 x 10-2 M based on the monomer unit). 105 106 107
pyridinium salts of PMAP were ranged from 14 to k, which corresponds to 0.19 to 0.13 S/cm in terms of conductivity (Table 1, entries 1-3). The sheet resistance of the drop-cast film was
3 108 109 110 111 112 113 114 115 116 117 118 119
120 121 122
measured by a four-point probe method. The film was formed by drop-casting the aqueous 2% (w/w) solution of the pyridinium salt of PMAP 1b (molar ratio = 1:2 based on the monomer unit) on a glass substrate. The sheet resistance was 3.8 x 106 /□. The spin-coating film was also formed with the aqueous 2% (w/w) solution of the pyridinium salt of PMAP 1b (molar ratio = 1:2 based on the monomer unit) on a glass substrate. The photo of the film was shown in Figure 4. It was a transparent light brown film. The thickness was 18 nm. The scanning electron microscopy (SEM) images of the spin-coating film were shown in Figure S3 in Supplementary Material. The uniformly formed surface of the film was observed. Table 1. Electrical resistance and conductivity for the drop-cast films of the aqueous 1% (w/w) suspension or solution of the pyridinium salts of PMAP 1b
147
University for the conductivity measurements by the four-point probe method, and Dr. H. Yamamoto and Prof. T. Kozawa at Osaka University for the film thickness measurements. We also thank Comprehensive Analysis Center of the Institute of Scientific and Industrial Research, Osaka University for the ICPMS measurements and SEM analysis.
148
Supplementary Material
142 143 144 145 146
150
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/ .
151
References and notes
149
152
1.
153
Entry 1 2 3 123 124 125
Molar equivalents of pyridinea 1 2 4
Suspension or solution Suspension Solution Solution
Electrical resistance (k) 14 20 20
Conductivity (S/cm)b 0.19 0.13 0.13
a
Based on the monomer unit. bConductivity was calculated on the assumption that the gap (see the below figure) was filled with the polymer. Therefore, the obtained value is the minimum value.
154 155
2. 3.
156 157
4.
158 159 160 161 162 163
5. 6.
164 165 166
7.
167 168 169 126
170 171
127
172 128
173 174
8.
175 176 177 178 179 180 181 182 183 184 185 186 187 129
188
Figure 4. Photo of the spin-coating film formed with the aqueous 2% (w/w) solution of the pyridinium salt of PMAP 1b (molar ratio = 1:2 based on the monomer unit) on a glass substrate (26 x 26 mm) and its thickness.
189 190 191 192 193 194
130 195 131 132 133 134 135 136 137 138
139
140 141
In conclusion, the self-doped conducting polyaniline PMAP 1b was successfully synthesized via oxidative polymerization. This is the first synthesis of the polyaniline bearing phosphonic acid directly attached to the backbone. Self-doping of PMAP 1b was clearly shown by UV-vis-NIR and ESR measurements. The pyridinium salt of PMAP 1b was water-soluble and its film exhibited conductivity. The electrical materials application of PMAP is now underway. Acknowledgments We thank Dr. T. Suenobu and Prof. S. Fukuzumi at Osaka University for the ESR measurements, Dr. R. Tsuji at Osaka
9.
196 197
10.
198 199 200 201 202
11.
203 204 205
12.
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