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Poly(3′,4′-dibutyl-α-terthiophene-phenylene-vinylene): a new soluble and dopable phenylene-vinylene-based conjugated polymer
ELSEVIER
Synthetic Metals 74 ( 1995) 71-74
Poly( 3’,4’-dibutyl-cu-terthiophene-phenylene-vinylene) : a new soluble and dopable phenylene-vinylene-based conjugated polymer Chenggang Wang a, Xusheng Xie a, Eugene LeGoff a, Joyce Albritton-Thomas b, Carl R. Kannewurf b, Mercouri G. Kanatzidis a,**1 aDepartment of Chemistry and Centerfor Fun&mental Materials Research, Michigan State University, East Lansing, MI 48824, USA h Department of Electrical Engineering and Computer Science, Northwestern University, Evanston, IL 60208-3118, USA Received 3 March 1995; accepted 26 April 1995
Abstract A new soluble and dopable copolymer consisting of 3’,4’-dibutyl-2,2’:5’,2”-terthiophene and phenylene-vinylene units has been designed and prepared via a Wittig reaction. This title copolymer is soluble in common organic solvents such as THF and CHCla, and can be doped with iodine achieving an electrical conductivity of about 3.2 X lo-* S/cm at room temperature. Films of this copolymer are electroactive and turn reversibly and rapidly from red to green-blue upon doping and undoping electrochemically. Keywords: Poly( 3’,4’-dibutyl-a-terthiophene-phenylene-vinylene);
Doping
1. Introduction
Conjugated polymers such as poly (arylenevinylene) s, polythiophenes and poly (p-phenylene) s [ 1] exhibit interesting electrical, nonlinear optical and electrooptical properties which make them good candidates for applications in rechargeable batteries [ 21, supercapacitors [ 31, field-effect transistors [ 41, sensors [ 51, electrochromic display devices [ 61 and light-emitting diodes (LEDs) [ 71. Since the discovery of polymer-based electroluminescent (EL) devices [ 81, tremendous effort has been focused on the design and synthesis of new soluble electro-active polymers to gain control of color and efficiency of light emission. Among a variety of polymer systems, p-phenylene-vinylene-based polymers are the most studied, possibly due to the fact that poly(p-phenylene-vinylene) (PPV) was the first to demonstrate electroluminescence [ 81. Different synthetic approaches have since emerged from several research groups, such as controlling the extent of conjugation length [ 93, incorporating isolated chromophors and non-coplanar structures into the polymer structure [ lo], producing saturated chain polymers with pendant conjugated side-groups [ 111 and synthesizing main chain polymers with intermittent sequences of conjugated and * Corresponding
author. ’ Camille and Henry Dreyfus Teacher Scholar 1993-95. Internet address: [email protected]. Fax: 517-353-1793. 0379-6779/95/$09.50 0 1995 Elsevier Science S.A. All rights reserved SSDI0379-6779(95)03348-N
non-conjugated segments [ 121. From a design and synthesis point of view, the Wittig reaction [ 131 is especially applicable to the PPV-based polymer system [ 143. Recently, two papers have demonstrated the use of appropriate Wittig reactions to synthesize PPV derivatives in order to vary the color of emitted light [ 151. (poly (DBPoly (3’,4’-dibutyl-2,2’:5’,2”-terthiophene) IT) ) is soluble in common organic solvents and shows interesting electrical and photoluminescent (PL) properties [ 161. This polymer is based on the monomer 3’,4’-dibutyl2,2’:5’,2”-terthiophene (DBTT, 1). Now we have successfully synthesized a dialdehyde derivative of 1, namely 2,5”-diformyl-3’,4’-dibutyl-2,2’:5,2”-terthiophene (DFDBT, 2)) which affords us a great opportunity to exploit the Wittig reaction to synthesize interesting new polymers by employing the appropriate bis-ylides.
1
2
The resulting tailor-made copolymers should lead to materi-
als with ‘tunable’properties, while maintaining the enhanced solubility imparted by the DB’IT building block.
C. Wang et al. /Synthetic
12
Metals 74 (1995) 71-74
CH=PPh3
ii 4
+
CHo
-
Fig. 1. Solid state electronic absorption spectra of solution-cast films of the. copolymer PBTPV at room temperature for neutral samples and samples doped with iodine. 5 PBTPV
Scheme 1. Reagents and conditions: (i) n-BuLi, dry THF, Nz; (ii) THF, Na, reflux, followed by precipitation with MeOH.
In this communication we report the synthesis and characterisation of a new soluble conjugated copolymer consisting of 3’,4’-dibutyl-2,2’:5’,2”-terthiophene and phenylene-vinylene units *.
2. Experimental and results The copolymer, poly(3’,4’-dibutyl-2,2’:5’,2”-terthiophene- 1,2-ethenylene- 1,Cphenylene- 1,2-ethenylene ( PBTPV) was prepared as shown in Scheme 1. The material is red in the neutral state and is polycrystalline as indicated by Xray powder diffraction (XRD). It is soluble in common organic solvents such as THF and CHC&. The average molecular weights of PBTPV measured by the gel permeation chromatography (GPC) method (using polystyrene as calibration standards) are jt?,,_ 1.43 X 103, & _ 1.89 X lo3 with polydispersity of 1.32. The elemental analysis and the spectral properties of the PBTPV are consistent with the expected structure ‘. Thus, the strong absorption band in the IR spectrum of the dialdehyde comonomer 2 at 1660 cm- ’ (-CHO) is absent in the spectrum of PBTPV, indicating that the aldehyde group has reacted with the ylide. In addition, the ‘H NMR peak at S 9.89 in the spectrum of the dialdehyde 2 is absent in that of PBTPV. The UV-Vis-NIR spectrum of PBTPV shows an absorption maximum at 450 nm in THF solution with an onset at 536 nm. A film cast from THF solution shows an absorption band with the same maximum as in solution, but the onset of absorption (i.e. bandgap of PBTPV) shifts to 605 nm (about 2.0 eV) (see Fig. 1). The bandgap of PBTPV is comparable to that of poly (DBTT) ( Eg - 2.0 eV) [ 161 and smaller than * The reaction of 1,4-xylenebis(triphenylphosphonium bromide) 3 with n-BuLi under NZ in situ afforded the bis-ylide 4. Subsequently, the Wittig reaction of 4 with dialdehyde 2 provide copolymer 5 (PBTPV) in 77.8% yield. Anal. Calc. for CaeH3,,S3(repeat unit): C, 74.07; H, 6.17. Found: C, 71.53; H, 6.34%. This copolymer can be considered as a hybrid polymer between polythiophenes and poly(p-phenylene-vinylene)s.
that of PPV (E, - 2.5 eV) [ 171 Photoexcitation (A,, = 350 nm) of the PBTPV in dilute THF solution at 23 “C results in broad-band luminescence (halfwidth about 0.20 eV) with a peak maximum at 2.23 eV (555 nm). The corresponding photoluminescence maximum of PPV [ 151 was found at 550 nm and that of poly (DBTT) [ 161 at 557 nm (for fraction I). Thermogravimetric analysis (TGA) of PBTPV shows that it is stable up to 378 “C under nitrogen and 260 “C under oxygen atmosphere. Differential scanning calorimetry (DSC) measurements between 30 and 300 “C detected no phase transitions. PBTPV can be doped readily by exposure to iodine vapor or dipping in acetonitrile solutions of iodine 3. Upon doping, the red films turn to dark brown. The solid state W-VisNIR absorption spectrum of a doped film of PBTPV cast from THF solution on a quartz slide is shown in Fig. 1. The r* ti absorption band at 2.76 eV loses intensity and shifts to slightly higher energy, while two new subgap absorption bands appear at 0.80 and 1.7 1 eV. This result is consistent with charge storage predominantly in bipolarons [ 181. The electrical conductivity of the iodine-doped material was measured by the standard four-probe method on pressed pellets as a function of temperature (Fig. 2). While the neutral form of PBTPV is nearly insulating (cr < lo-” S/cm at room temperature), the doped form has an electrical conductivity of about 3.2 X lo-* S/cm at room temperature. Films of PBTPV were studied by cyclic voltammetry (CV) on various electrodes (i.e. Pt and ITO). The polymer films turn green-blue upon anodic oxidation in a process 3Doping experiments of the copolymer PBTPV: (a) doping with iodine vapor. A film of the copolymer PBTPV, solution (THF) cast on a quarts slide, was put into a closed chamber filled with iodine crystal and stored for 0.5 h. The original orange film turned dark brown. (b) Doping with iodine in acetonitrile. To a stirred 45 ml 0.1 M iodine acetonitrile solution, 0.026 g red solid of the copolymer PBTPV was added. The ted powder turned black immediately. After sting for 10 h, the black solid (dark green) was collected, washed several times with acetonitrile and vacuum dried overnight. The yield was quantitative. The sample was pressed into pellets for the electrical conductivity measurements. The doping level is about 0.61 13per repeat unit, as estimated from the sulfur-to-iodine ratio obtained by the SEM-EDS method.
C. Wang et al. /Synthetic
Metals 74 (1995) 71-74
13
spaced by flexible-chain aromatic and aliphatic segments [191.
Acknowledgments
-12
Financial support from the National Science Foundation (DMR-93-06385) and the Center for Fundamental Materials Research at Michigan State University is gratefully acknowledged. At Northwestern University this work made use of Central Facilities supported by the NSF through the Materials Research Center (DMR-9 l-2052 1) .
~s,,,,,,,,,,,,,,,,,,,,,,,,,,,,I 0
50
100
150 200 Temperature (K)
250
300
Fig. 2. Four-probe variable-temperature electrical conductivity of the copolymer PBTPV doped with iodine.
References [ 1] (a) J. Roncali, Chem. Rev., 92 ( 1992) 71 l-738 and Refs. therein; (b) T.A. Skotheim (ed.), Handbook of Conducting Polymers, Vols. 1 and 2, Marcel Dekker, New York, 1986; (c) T.A. Skotheim (ed.), Electroresponsive Molecular and Polymeric System, Vols. 1 and 2, Marcel Dekker, New York, 1991. [ 21 (a) T. Nakajima and T. Kawagoe, Synth. Met., 28 ( 1989) C629; (b) M. Mizumoto, M. Namba, S. Nishimura, H. Miyadera, M. Kosehi and Y. Kobayashi, Synth. Met., 28 (1989) C639. [3] (a) S.C. Huang,S.M. Huang, H. NgandR.B. Kaner,Synth. Met., 5557 ( 1993) 4047; (b) R.H. Baughman, Makromol. Chem., Macromol. Symp., 51 (1991) 193; (c) B.E. Conway, J. Electrochem. Sot., 138 (1991) 1.539; (d) D.J. Guerrero, X. Ren and J.P. Ferraris, Chem. Mater., 6 (1994) 1437-1443. [4] G. Horowitz, D. Fichou, X. Peng and F. Gamier, Synth. Met., 41-43
Fig. 3. Typical cyclic voltammogmm of a solution-cast film of PBTPV on a pt electrode in CH,CN/O.l M (Bu,N)ClO,,. Scan rate 20 mV/s; potential vs. SCE.
which shows a current maximum at 0.84 V versus SCE (using a Pt electrode at 0.020 V/s in 0.1 M Bu,NCIO, acetonitrile solution). The color returns to red in the reverse scan which shows a current maximum at 0.72 V versus SCE (see Fig. 3). At higher scan rates (up to 1 V/s), the CV curves are less well resolved, but the observed color changes continued to respond well to the potential changes. The electrochemical properties of PBTPV suggest that it may have application in electrochromic devices. A full characterization of this material is in progress [ 191.
(1991) 1127 and Refs. therein. [5] (a) A. Galal, H.B. Mark, Jr. and P.L. Bishop, Proc. Polym. Mater. Sci. Eng.. 71 (1994) 654-655; (b) A. Guiseppi-Elieand A.M. Wilson, Proc. Polym. Mater. Sci. Eng., 71 (1994) 381-382. [6] (a) S. Panero, S. Passerini and B. Scrosati, Mol. Cryst. Liq. Cryst., 229 ( 1993) 97; (b) M.T. Nguyen and L.H. Dao, J. Electrochem. Sot.. 136 (1989) 2131. [7] (a) D. Braun, G. Gustafsson, D. McBranch and A.J. Heeger, J. Appl. Phys., 72 (1992) 564-568; (b) G. Gustafsson, Y. Cao, G.M. Tracy, F. Klavetter, N. Colaneri and A.J. Heeger, Nature, 357 (1992) 477; (c) G. Ohmori, M. Uchida and K. Yoshino, Solid State Commun., 80 ( 1991) 605; (d) H. Vestweber, A. Greeiner, U. Lemmer, R.F. Mahrt, R. Richert, W. Heitz and H. Bassler, Adv. Mater., 4 (1992) 661. [8] J.H. Burroughes, D.D.C. Bradley, A.R. Brown, R.N. Marks, K. Mackay, R.H. Friend, P.L. Burn and A.B. Holmes, Namre, 347 ( 1990) 539-541. [PI (a) P.L. Bum, A.B. Holmes, A. Kraft, D.D.C. Bradley, A.R. Brown and R.H. Friend, J. Chem. Sot., Chem. Commun., (1990) 32; (b) C. Zhang, D. Braun and A.J. Heeger, J. Appl. Phys., 73 ( 1993) 51775180.
3. Conclusions A new soluble copolymer has been designed and prepared by combining conjugated terthiophene units with phenylenevinylene units through the Wittigreaction. The product shows interesting fully reversible electrochromic behavior with reasonably high electrical conductivity in the doped form. The basic strategy in the synthesis of this material can be applied to synthesize other useful new copolymers containing the rigid conjugated block 3’,4’-dibutyl-2,2’:5’,2”terthiophene
[lo] H.V. Seggem, P. Schmidt-Winkel, C. Zhang, K. Pakbaz, B. Kraabel, A.J. Heeger and H.-W. Schmidt, Polym. Prepr., 34 (1993) 532-533. [ 111 (a) T.T. Trial and R.K. Khanna, Polym. Prepr., 34 (1993) 869-870; (b) R.K. KhannaandH. Cui, Macromolecules, 26 (1993) 70767078; (c) R.K. Khanna and N. Bhingare, Chem. Marer., 5 (1993) 899-901; (d) J. Ying and R.K. Khanna, Polym. Prepr., 35 ( 1994) 753-754. 1121 (a) P.L. Bum, A.B. Holmes, A. Kraft, D.D.C. Bradley, A.R. Brown, R.H. Friend and R.H. Gymer, Nature, 356 ( 1992) 47 and Refs. therein; (b) G.G. Malliaras, J.K. Herrema, J. Wildeman, R.H. Wieringa, R.E. Gill, S. Lampoura and G. Hadziioannou, Adv. Mater., 5 (1993) 721123. [13] J. March (ed.), Advanced Organic Chemistry, Wiley, New York, 3rd edn., 1985, pp. 845-854 and Refs. therein.
14
C. Wang et al. /Synthetic Metals 74 (1995) 71-74
[14] (a) K.-Y. Jen, M.P. Cava, W.S. Huang and A.G. MacDiannid, J. Chem. Sot., Chem. Commun., (1983) 1502-1503; (b) W.S. Huang, K.-Y. Jen, M. Angelopoulos, A.G. MacDiarmid and M.P. Cava, Mol. Cryst. Liq. Ctyst., 189 (1990) 237-254. [ 151 (a) M.F. Hay, Y. Yang and F.L. Klavetter, Pofym. Prepr., 35 ( 1994) 293-294; (b) Z. Yang, I. Sokolik and F.E. Karasz, Macromolecules, 26(1993)1188-1190. [ 161 (a) C. Wang, M.E. Benz, E. LeGoff, J.L. Scbindler, C.R. Kannewurf and M.G. Kanatzidis, Polym. Prepr., 34 (1993) 422-423; (b) C.
Wang, M.E. Benz, E. LeGoff, J.L. Scbindler, J. Allbritton-Thomas, CR. Kannewurf and M.G. Kanatzidis, Chem. Mater., 6 (1994) 401411. [17] (a) D.D.C. Bradley, N.F. Colaneri and R.H. Friend, Synch. Met., 29 (1989) E121-E127; (b) R.H. Friend, D.D.C. Bradley and P.D. Townsend, J. Phys. D: Appl. Phys., 20 (1987) 1367. [18] A.O. Patil, A.J. Heeger and F. Wudl, Chem. Rev., 88 ( 1988) 183200. [ 191 C. Wang, X. Xie, E. LeGoff and M.G. Kanatzidis, work in progress.
Synthetic Metals 74 ( 1995) 71-74
Poly( 3’,4’-dibutyl-cu-terthiophene-phenylene-vinylene) : a new soluble and dopable phenylene-vinylene-based conjugated polymer Chenggang Wang a, Xusheng Xie a, Eugene LeGoff a, Joyce Albritton-Thomas b, Carl R. Kannewurf b, Mercouri G. Kanatzidis a,**1 aDepartment of Chemistry and Centerfor Fun&mental Materials Research, Michigan State University, East Lansing, MI 48824, USA h Department of Electrical Engineering and Computer Science, Northwestern University, Evanston, IL 60208-3118, USA Received 3 March 1995; accepted 26 April 1995
Abstract A new soluble and dopable copolymer consisting of 3’,4’-dibutyl-2,2’:5’,2”-terthiophene and phenylene-vinylene units has been designed and prepared via a Wittig reaction. This title copolymer is soluble in common organic solvents such as THF and CHCla, and can be doped with iodine achieving an electrical conductivity of about 3.2 X lo-* S/cm at room temperature. Films of this copolymer are electroactive and turn reversibly and rapidly from red to green-blue upon doping and undoping electrochemically. Keywords: Poly( 3’,4’-dibutyl-a-terthiophene-phenylene-vinylene);
Doping
1. Introduction
Conjugated polymers such as poly (arylenevinylene) s, polythiophenes and poly (p-phenylene) s [ 1] exhibit interesting electrical, nonlinear optical and electrooptical properties which make them good candidates for applications in rechargeable batteries [ 21, supercapacitors [ 31, field-effect transistors [ 41, sensors [ 51, electrochromic display devices [ 61 and light-emitting diodes (LEDs) [ 71. Since the discovery of polymer-based electroluminescent (EL) devices [ 81, tremendous effort has been focused on the design and synthesis of new soluble electro-active polymers to gain control of color and efficiency of light emission. Among a variety of polymer systems, p-phenylene-vinylene-based polymers are the most studied, possibly due to the fact that poly(p-phenylene-vinylene) (PPV) was the first to demonstrate electroluminescence [ 81. Different synthetic approaches have since emerged from several research groups, such as controlling the extent of conjugation length [ 93, incorporating isolated chromophors and non-coplanar structures into the polymer structure [ lo], producing saturated chain polymers with pendant conjugated side-groups [ 111 and synthesizing main chain polymers with intermittent sequences of conjugated and * Corresponding
author. ’ Camille and Henry Dreyfus Teacher Scholar 1993-95. Internet address: [email protected]. Fax: 517-353-1793. 0379-6779/95/$09.50 0 1995 Elsevier Science S.A. All rights reserved SSDI0379-6779(95)03348-N
non-conjugated segments [ 121. From a design and synthesis point of view, the Wittig reaction [ 131 is especially applicable to the PPV-based polymer system [ 143. Recently, two papers have demonstrated the use of appropriate Wittig reactions to synthesize PPV derivatives in order to vary the color of emitted light [ 151. (poly (DBPoly (3’,4’-dibutyl-2,2’:5’,2”-terthiophene) IT) ) is soluble in common organic solvents and shows interesting electrical and photoluminescent (PL) properties [ 161. This polymer is based on the monomer 3’,4’-dibutyl2,2’:5’,2”-terthiophene (DBTT, 1). Now we have successfully synthesized a dialdehyde derivative of 1, namely 2,5”-diformyl-3’,4’-dibutyl-2,2’:5,2”-terthiophene (DFDBT, 2)) which affords us a great opportunity to exploit the Wittig reaction to synthesize interesting new polymers by employing the appropriate bis-ylides.
1
2
The resulting tailor-made copolymers should lead to materi-
als with ‘tunable’properties, while maintaining the enhanced solubility imparted by the DB’IT building block.
C. Wang et al. /Synthetic
12
Metals 74 (1995) 71-74
CH=PPh3
ii 4
+
CHo
-
Fig. 1. Solid state electronic absorption spectra of solution-cast films of the. copolymer PBTPV at room temperature for neutral samples and samples doped with iodine. 5 PBTPV
Scheme 1. Reagents and conditions: (i) n-BuLi, dry THF, Nz; (ii) THF, Na, reflux, followed by precipitation with MeOH.
In this communication we report the synthesis and characterisation of a new soluble conjugated copolymer consisting of 3’,4’-dibutyl-2,2’:5’,2”-terthiophene and phenylene-vinylene units *.
2. Experimental and results The copolymer, poly(3’,4’-dibutyl-2,2’:5’,2”-terthiophene- 1,2-ethenylene- 1,Cphenylene- 1,2-ethenylene ( PBTPV) was prepared as shown in Scheme 1. The material is red in the neutral state and is polycrystalline as indicated by Xray powder diffraction (XRD). It is soluble in common organic solvents such as THF and CHC&. The average molecular weights of PBTPV measured by the gel permeation chromatography (GPC) method (using polystyrene as calibration standards) are jt?,,_ 1.43 X 103, & _ 1.89 X lo3 with polydispersity of 1.32. The elemental analysis and the spectral properties of the PBTPV are consistent with the expected structure ‘. Thus, the strong absorption band in the IR spectrum of the dialdehyde comonomer 2 at 1660 cm- ’ (-CHO) is absent in the spectrum of PBTPV, indicating that the aldehyde group has reacted with the ylide. In addition, the ‘H NMR peak at S 9.89 in the spectrum of the dialdehyde 2 is absent in that of PBTPV. The UV-Vis-NIR spectrum of PBTPV shows an absorption maximum at 450 nm in THF solution with an onset at 536 nm. A film cast from THF solution shows an absorption band with the same maximum as in solution, but the onset of absorption (i.e. bandgap of PBTPV) shifts to 605 nm (about 2.0 eV) (see Fig. 1). The bandgap of PBTPV is comparable to that of poly (DBTT) ( Eg - 2.0 eV) [ 161 and smaller than * The reaction of 1,4-xylenebis(triphenylphosphonium bromide) 3 with n-BuLi under NZ in situ afforded the bis-ylide 4. Subsequently, the Wittig reaction of 4 with dialdehyde 2 provide copolymer 5 (PBTPV) in 77.8% yield. Anal. Calc. for CaeH3,,S3(repeat unit): C, 74.07; H, 6.17. Found: C, 71.53; H, 6.34%. This copolymer can be considered as a hybrid polymer between polythiophenes and poly(p-phenylene-vinylene)s.
that of PPV (E, - 2.5 eV) [ 171 Photoexcitation (A,, = 350 nm) of the PBTPV in dilute THF solution at 23 “C results in broad-band luminescence (halfwidth about 0.20 eV) with a peak maximum at 2.23 eV (555 nm). The corresponding photoluminescence maximum of PPV [ 151 was found at 550 nm and that of poly (DBTT) [ 161 at 557 nm (for fraction I). Thermogravimetric analysis (TGA) of PBTPV shows that it is stable up to 378 “C under nitrogen and 260 “C under oxygen atmosphere. Differential scanning calorimetry (DSC) measurements between 30 and 300 “C detected no phase transitions. PBTPV can be doped readily by exposure to iodine vapor or dipping in acetonitrile solutions of iodine 3. Upon doping, the red films turn to dark brown. The solid state W-VisNIR absorption spectrum of a doped film of PBTPV cast from THF solution on a quartz slide is shown in Fig. 1. The r* ti absorption band at 2.76 eV loses intensity and shifts to slightly higher energy, while two new subgap absorption bands appear at 0.80 and 1.7 1 eV. This result is consistent with charge storage predominantly in bipolarons [ 181. The electrical conductivity of the iodine-doped material was measured by the standard four-probe method on pressed pellets as a function of temperature (Fig. 2). While the neutral form of PBTPV is nearly insulating (cr < lo-” S/cm at room temperature), the doped form has an electrical conductivity of about 3.2 X lo-* S/cm at room temperature. Films of PBTPV were studied by cyclic voltammetry (CV) on various electrodes (i.e. Pt and ITO). The polymer films turn green-blue upon anodic oxidation in a process 3Doping experiments of the copolymer PBTPV: (a) doping with iodine vapor. A film of the copolymer PBTPV, solution (THF) cast on a quarts slide, was put into a closed chamber filled with iodine crystal and stored for 0.5 h. The original orange film turned dark brown. (b) Doping with iodine in acetonitrile. To a stirred 45 ml 0.1 M iodine acetonitrile solution, 0.026 g red solid of the copolymer PBTPV was added. The ted powder turned black immediately. After sting for 10 h, the black solid (dark green) was collected, washed several times with acetonitrile and vacuum dried overnight. The yield was quantitative. The sample was pressed into pellets for the electrical conductivity measurements. The doping level is about 0.61 13per repeat unit, as estimated from the sulfur-to-iodine ratio obtained by the SEM-EDS method.
C. Wang et al. /Synthetic
Metals 74 (1995) 71-74
13
spaced by flexible-chain aromatic and aliphatic segments [191.
Acknowledgments
-12
Financial support from the National Science Foundation (DMR-93-06385) and the Center for Fundamental Materials Research at Michigan State University is gratefully acknowledged. At Northwestern University this work made use of Central Facilities supported by the NSF through the Materials Research Center (DMR-9 l-2052 1) .
~s,,,,,,,,,,,,,,,,,,,,,,,,,,,,I 0
50
100
150 200 Temperature (K)
250
300
Fig. 2. Four-probe variable-temperature electrical conductivity of the copolymer PBTPV doped with iodine.
References [ 1] (a) J. Roncali, Chem. Rev., 92 ( 1992) 71 l-738 and Refs. therein; (b) T.A. Skotheim (ed.), Handbook of Conducting Polymers, Vols. 1 and 2, Marcel Dekker, New York, 1986; (c) T.A. Skotheim (ed.), Electroresponsive Molecular and Polymeric System, Vols. 1 and 2, Marcel Dekker, New York, 1991. [ 21 (a) T. Nakajima and T. Kawagoe, Synth. Met., 28 ( 1989) C629; (b) M. Mizumoto, M. Namba, S. Nishimura, H. Miyadera, M. Kosehi and Y. Kobayashi, Synth. Met., 28 (1989) C639. [3] (a) S.C. Huang,S.M. Huang, H. NgandR.B. Kaner,Synth. Met., 5557 ( 1993) 4047; (b) R.H. Baughman, Makromol. Chem., Macromol. Symp., 51 (1991) 193; (c) B.E. Conway, J. Electrochem. Sot., 138 (1991) 1.539; (d) D.J. Guerrero, X. Ren and J.P. Ferraris, Chem. Mater., 6 (1994) 1437-1443. [4] G. Horowitz, D. Fichou, X. Peng and F. Gamier, Synth. Met., 41-43
Fig. 3. Typical cyclic voltammogmm of a solution-cast film of PBTPV on a pt electrode in CH,CN/O.l M (Bu,N)ClO,,. Scan rate 20 mV/s; potential vs. SCE.
which shows a current maximum at 0.84 V versus SCE (using a Pt electrode at 0.020 V/s in 0.1 M Bu,NCIO, acetonitrile solution). The color returns to red in the reverse scan which shows a current maximum at 0.72 V versus SCE (see Fig. 3). At higher scan rates (up to 1 V/s), the CV curves are less well resolved, but the observed color changes continued to respond well to the potential changes. The electrochemical properties of PBTPV suggest that it may have application in electrochromic devices. A full characterization of this material is in progress [ 191.
(1991) 1127 and Refs. therein. [5] (a) A. Galal, H.B. Mark, Jr. and P.L. Bishop, Proc. Polym. Mater. Sci. Eng.. 71 (1994) 654-655; (b) A. Guiseppi-Elieand A.M. Wilson, Proc. Polym. Mater. Sci. Eng., 71 (1994) 381-382. [6] (a) S. Panero, S. Passerini and B. Scrosati, Mol. Cryst. Liq. Cryst., 229 ( 1993) 97; (b) M.T. Nguyen and L.H. Dao, J. Electrochem. Sot.. 136 (1989) 2131. [7] (a) D. Braun, G. Gustafsson, D. McBranch and A.J. Heeger, J. Appl. Phys., 72 (1992) 564-568; (b) G. Gustafsson, Y. Cao, G.M. Tracy, F. Klavetter, N. Colaneri and A.J. Heeger, Nature, 357 (1992) 477; (c) G. Ohmori, M. Uchida and K. Yoshino, Solid State Commun., 80 ( 1991) 605; (d) H. Vestweber, A. Greeiner, U. Lemmer, R.F. Mahrt, R. Richert, W. Heitz and H. Bassler, Adv. Mater., 4 (1992) 661. [8] J.H. Burroughes, D.D.C. Bradley, A.R. Brown, R.N. Marks, K. Mackay, R.H. Friend, P.L. Burn and A.B. Holmes, Namre, 347 ( 1990) 539-541. [PI (a) P.L. Bum, A.B. Holmes, A. Kraft, D.D.C. Bradley, A.R. Brown and R.H. Friend, J. Chem. Sot., Chem. Commun., (1990) 32; (b) C. Zhang, D. Braun and A.J. Heeger, J. Appl. Phys., 73 ( 1993) 51775180.
3. Conclusions A new soluble copolymer has been designed and prepared by combining conjugated terthiophene units with phenylenevinylene units through the Wittigreaction. The product shows interesting fully reversible electrochromic behavior with reasonably high electrical conductivity in the doped form. The basic strategy in the synthesis of this material can be applied to synthesize other useful new copolymers containing the rigid conjugated block 3’,4’-dibutyl-2,2’:5’,2”terthiophene
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