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Soluble conjugated copolymers constituted of pyridine and phenylene units
ELSEVIER
Synthetic Metals 102 (1999) 1524-1525
Soluble conjugated copolymers constituted of pyridine and phenylene units Susumu Tanakaa, Masami Kumeib a National
Instirure of Materials
and Chemical Research; l-l Higashi, Tsukuba 305-8565, Japan
b Stanley Electric Co., Ltd. 5-9-5 Tokodai, Tsukuba 300-2635, Japan
Abstract Poly(2,5-dihexyl-1,4-phenylene-alt-2,5-pyridinediyl) (PDHP-2,5-Py) was prepared in a high yield by the Suzuki reaction of 2,5dihexylbenzene-1,4-bisboronic acid and p-dibromopyridine. The copolymer was soluble in organic solvents such as chloroform, THF and dichloromethane. GPC indicated that it had an average molecular weight of 1.1~10~. A cast film deposited on a platinum plate was used for cyclic voltammetry. The filmshowed a cathodic peak at -2.2 V (vs. Ag wire). It wasgreen below the reduction potential and transparent in the neutral state. Keywords: Couplingreactions;Transition-metal-catalyzed
reactions; Electroctrochemical
type doping[4-61. Although PPPs have been considered for applications in various fields of optoelectronics[7,8], it is difficult to produce films by chemical techniques because of its insolubility.
1. Introduction Many studies have been devoted to conjugated polymers from scientific and industrial points of view because of their interesting electrical and optical properties[l-31. However, most of the studies have been conducted with p-type conjugated polymers produced by chemical and electrochemical oxidation. Studies on n-type conjugated polymers have been limited in spite of their importance. Poly-p-phenylene (PPP) has been attractive because of excellent thermal stability of the neutral polymer and possibility of p- and n-
BuLi
Br
doping; Other conjugated polymers
-
BP%)3 -
In this study, we report the preparation of new conjugated alternate copolymers constituted of pyridine and phenylene units by palladium catalyzed coupling of 2,5-dihextylbenzene-1,4bisboronic acid with 2,5-dibromopyridine (Scheme 1). The copolymer was soluble in organic solvents such as chloroform, THF and dichloromethane. GPC indicated that it had an average molecular weight of 1.1X104. The cyclic voltammogram of the polymer film showed reversible n-type doping and undoping with a color change between transparent (undoped) and green (n-doped).
2. Results and Discussion 2.1. Procedure of poly(2,5-dihexyl-1,4-phenyleneah-2,5pyridinediyl) (PDHP-2,5-Py) by palladium-catalyzed coupling Scheme I
Scheme 1. Preparation of poly(2,5-dihexyl-1,4-phenyleneneaft-2,5-pyridinediyl) (PDHP-2,5-Py)
1,4-Dihexylbenzene-2,5-bisboronic acid was prepared as previously reported[9,10]. A mixture of 2,5-dibromopyridine (0.237 g, 1.0 mmol), tetrakis(triphenylphosphine) palladium(O) (34.6 mg, 0.03 mmol)and an aqueous solution of Na2C03 (1.2 ml of a 2M solution) was stirred in 2 ml of toluene at room temperature under argon. An argon-purged solution of 1,4-dihexylbenzene-2,5-
0379-6779/99/$ - see front matter 0 1999 Elsevier Science S.A. All rights reserved. PII: SO379-6779(98)01051-O
S. Tanaka,
M. Kumei
I Synthetic
bisboronicacid (0.367 g, 1.1 mmol) in 2.5 ml ofethanol was added. The polymerization was conducted overnight at 80°C. The residue after evaporation of the solvent was poured into 20 ml of acetone and washed twice with 30 ml of 1 N HCI to afford light yellow powder. Yield: 0.301 g (94%). In the same way, poly(2,5-dihexyl-1,4phenylene-all-2,6-pyridinediyl) (PDHP-2,6-Py) was obtained using 2,6-dibromopyridine instead of 2,5dibromopyridine. Yield: 0.308 g (96%). Thus, this palladium catalyzed coupling reaction of dibromide with bisboronic acid was found to give an alternate copolymer in an excellent high yield. 2.2. FTlR and UV-VIS
spectra
Fig. 1 shows FTlR spectra of 2,5dibromopyridine, 1,4dihexylbenzene-2,5-bisboronic acid and PDHP-2,5-Py. 2,5dibromopyridine has a band at 482 cm-‘, assignable to a C-Br bond. Two bands were observed for the bisboronicacid at 1336 and 3300 cm-‘, due to the stretching vibrations of B-O and O-H bonds, respectively. These bands almost disappeared in PDHP-2,5-Py, indicating that bromine and boronic acid reacted with each other to form a C-C bond. UV-VIS spectrum of PDHP-2,5-Py had a band at 292 nm and no absorption was found in visible regions, impling that the polymer film was transparent. With 2,5-dibromopyridine and 1,4-dihexylbenzene-2,5-bisboronic acid, peak positions existed at shorter wavelengths than that of the polymer. This indicates that ri -conjugation has developed in the polymer.
Metals
102 (1999)
1525
1524-1525
2..3. Cyclic voltammograms
of PDHP-2,5-Py
A cast film deposited on a platinum plate was used for cyclic voltammetry. Reference electrode was Ag wire and supporting electrolyte was a 0.2 mol/l Bu4NBF4 solution of acetonitrile. Fig. 2 shows the cyclic voltammograms of the polymer. A cathodic peak was found at -2.2 V and an anodic peak at -2.05 V. The film was transparent in the neutral state and green in the n-doped state. The value ofQ, exchanged during the redox cycle, was found to be 0.20 electron per monomeric unit, suggesting that PDHP-2,5-Py can be used as a charge storage material such as an electrode for secondary batteries.There was no peak at positive potential regions.
lopAl /P-V
-2.5
-2.0
-1.5
-1.0
E 1 V VS. Ag wire Fig. 2. CV of PDHP-2,5-Py with 0.2 molil Bu4NBF4 tonitrile. Sweep rate: 100 mV/s.
in ace-
References
> b
2000 Wavenumber
1200 I
400
cm-1
Fig. 1. FAIR spectra of (a) 2,5-dibromopyridine, (b) 1,4dihexylbenzene-2,5-bisboronicacid and (c) PDHP-2,5-Py.
[l] T.A.Skotheim, Ed., “HandbookofConductive Polymers”, Marcel Dekker, Inc., Base1 1989 [2] M.G.Kanatzidis, Chem. Eng. News, 68 (1990) 36 [3] J.R.Reynolds and M.Ponerantz, in “Electroresponsive Mole clar and Polymer Systems”,T.A.Skotheim, Ed., Marcel Dekker, Inc., Base], 1991, vol. 2, chapter4 [4] M.Satoh, K.Kaneto and K.Yoshino, J. Chem. Sot., Chem. Commum.,(1985)1629 [5] S.Aeiyach and P.C.Lacaze, J. Polym. Sci., Polym. Chem., 27 (1989)515 [6] A.Aboulkassium and C.Chevrot, Polymer, 30(1993)401 f7] G.Grem, GLeditzky, B.Ulrich and G.Leising, Synth. Met.,51 (1992)383 [8]Y.Yang,Q.PeiandA.J.Heeger,J.Appl.Phys.,79(1993)934 [9] R.Rehehn,A.-DSchluterand W.J.Feast,Synthesis,(1988)386 [lo] R.Rulkens, M.Schulze and G.Wegner, Macromol. Rapid Commun., 15(1994)669
Synthetic Metals 102 (1999) 1524-1525
Soluble conjugated copolymers constituted of pyridine and phenylene units Susumu Tanakaa, Masami Kumeib a National
Instirure of Materials
and Chemical Research; l-l Higashi, Tsukuba 305-8565, Japan
b Stanley Electric Co., Ltd. 5-9-5 Tokodai, Tsukuba 300-2635, Japan
Abstract Poly(2,5-dihexyl-1,4-phenylene-alt-2,5-pyridinediyl) (PDHP-2,5-Py) was prepared in a high yield by the Suzuki reaction of 2,5dihexylbenzene-1,4-bisboronic acid and p-dibromopyridine. The copolymer was soluble in organic solvents such as chloroform, THF and dichloromethane. GPC indicated that it had an average molecular weight of 1.1~10~. A cast film deposited on a platinum plate was used for cyclic voltammetry. The filmshowed a cathodic peak at -2.2 V (vs. Ag wire). It wasgreen below the reduction potential and transparent in the neutral state. Keywords: Couplingreactions;Transition-metal-catalyzed
reactions; Electroctrochemical
type doping[4-61. Although PPPs have been considered for applications in various fields of optoelectronics[7,8], it is difficult to produce films by chemical techniques because of its insolubility.
1. Introduction Many studies have been devoted to conjugated polymers from scientific and industrial points of view because of their interesting electrical and optical properties[l-31. However, most of the studies have been conducted with p-type conjugated polymers produced by chemical and electrochemical oxidation. Studies on n-type conjugated polymers have been limited in spite of their importance. Poly-p-phenylene (PPP) has been attractive because of excellent thermal stability of the neutral polymer and possibility of p- and n-
BuLi
Br
doping; Other conjugated polymers
-
BP%)3 -
In this study, we report the preparation of new conjugated alternate copolymers constituted of pyridine and phenylene units by palladium catalyzed coupling of 2,5-dihextylbenzene-1,4bisboronic acid with 2,5-dibromopyridine (Scheme 1). The copolymer was soluble in organic solvents such as chloroform, THF and dichloromethane. GPC indicated that it had an average molecular weight of 1.1X104. The cyclic voltammogram of the polymer film showed reversible n-type doping and undoping with a color change between transparent (undoped) and green (n-doped).
2. Results and Discussion 2.1. Procedure of poly(2,5-dihexyl-1,4-phenyleneah-2,5pyridinediyl) (PDHP-2,5-Py) by palladium-catalyzed coupling Scheme I
Scheme 1. Preparation of poly(2,5-dihexyl-1,4-phenyleneneaft-2,5-pyridinediyl) (PDHP-2,5-Py)
1,4-Dihexylbenzene-2,5-bisboronic acid was prepared as previously reported[9,10]. A mixture of 2,5-dibromopyridine (0.237 g, 1.0 mmol), tetrakis(triphenylphosphine) palladium(O) (34.6 mg, 0.03 mmol)and an aqueous solution of Na2C03 (1.2 ml of a 2M solution) was stirred in 2 ml of toluene at room temperature under argon. An argon-purged solution of 1,4-dihexylbenzene-2,5-
0379-6779/99/$ - see front matter 0 1999 Elsevier Science S.A. All rights reserved. PII: SO379-6779(98)01051-O
S. Tanaka,
M. Kumei
I Synthetic
bisboronicacid (0.367 g, 1.1 mmol) in 2.5 ml ofethanol was added. The polymerization was conducted overnight at 80°C. The residue after evaporation of the solvent was poured into 20 ml of acetone and washed twice with 30 ml of 1 N HCI to afford light yellow powder. Yield: 0.301 g (94%). In the same way, poly(2,5-dihexyl-1,4phenylene-all-2,6-pyridinediyl) (PDHP-2,6-Py) was obtained using 2,6-dibromopyridine instead of 2,5dibromopyridine. Yield: 0.308 g (96%). Thus, this palladium catalyzed coupling reaction of dibromide with bisboronic acid was found to give an alternate copolymer in an excellent high yield. 2.2. FTlR and UV-VIS
spectra
Fig. 1 shows FTlR spectra of 2,5dibromopyridine, 1,4dihexylbenzene-2,5-bisboronic acid and PDHP-2,5-Py. 2,5dibromopyridine has a band at 482 cm-‘, assignable to a C-Br bond. Two bands were observed for the bisboronicacid at 1336 and 3300 cm-‘, due to the stretching vibrations of B-O and O-H bonds, respectively. These bands almost disappeared in PDHP-2,5-Py, indicating that bromine and boronic acid reacted with each other to form a C-C bond. UV-VIS spectrum of PDHP-2,5-Py had a band at 292 nm and no absorption was found in visible regions, impling that the polymer film was transparent. With 2,5-dibromopyridine and 1,4-dihexylbenzene-2,5-bisboronic acid, peak positions existed at shorter wavelengths than that of the polymer. This indicates that ri -conjugation has developed in the polymer.
Metals
102 (1999)
1525
1524-1525
2..3. Cyclic voltammograms
of PDHP-2,5-Py
A cast film deposited on a platinum plate was used for cyclic voltammetry. Reference electrode was Ag wire and supporting electrolyte was a 0.2 mol/l Bu4NBF4 solution of acetonitrile. Fig. 2 shows the cyclic voltammograms of the polymer. A cathodic peak was found at -2.2 V and an anodic peak at -2.05 V. The film was transparent in the neutral state and green in the n-doped state. The value ofQ, exchanged during the redox cycle, was found to be 0.20 electron per monomeric unit, suggesting that PDHP-2,5-Py can be used as a charge storage material such as an electrode for secondary batteries.There was no peak at positive potential regions.
lopAl /P-V
-2.5
-2.0
-1.5
-1.0
E 1 V VS. Ag wire Fig. 2. CV of PDHP-2,5-Py with 0.2 molil Bu4NBF4 tonitrile. Sweep rate: 100 mV/s.
in ace-
References
> b
2000 Wavenumber
1200 I
400
cm-1
Fig. 1. FAIR spectra of (a) 2,5-dibromopyridine, (b) 1,4dihexylbenzene-2,5-bisboronicacid and (c) PDHP-2,5-Py.
[l] T.A.Skotheim, Ed., “HandbookofConductive Polymers”, Marcel Dekker, Inc., Base1 1989 [2] M.G.Kanatzidis, Chem. Eng. News, 68 (1990) 36 [3] J.R.Reynolds and M.Ponerantz, in “Electroresponsive Mole clar and Polymer Systems”,T.A.Skotheim, Ed., Marcel Dekker, Inc., Base], 1991, vol. 2, chapter4 [4] M.Satoh, K.Kaneto and K.Yoshino, J. Chem. Sot., Chem. Commum.,(1985)1629 [5] S.Aeiyach and P.C.Lacaze, J. Polym. Sci., Polym. Chem., 27 (1989)515 [6] A.Aboulkassium and C.Chevrot, Polymer, 30(1993)401 f7] G.Grem, GLeditzky, B.Ulrich and G.Leising, Synth. Met.,51 (1992)383 [8]Y.Yang,Q.PeiandA.J.Heeger,J.Appl.Phys.,79(1993)934 [9] R.Rehehn,A.-DSchluterand W.J.Feast,Synthesis,(1988)386 [lo] R.Rulkens, M.Schulze and G.Wegner, Macromol. Rapid Commun., 15(1994)669