π-Conjugated donor-acceptor copolymers constituted of π-excessive and π-deficient arylene units. Optical and electrochemical properties in relation to CT structure of the polymer

Article abstract of DOI:10.1021/ja961550t

Various π-conjugated copolymers constituted of π-excessive thiophene, selenophene, or furan units (Ar) and π-deficient pyridine or quinoxaline (Ar') units have been prepared in high yields by the following organometallic polycondensation methods: (i) n X-Ar-Ar'-X + n Ni(0)Lm → (Ar-Ar')(n) (X = halogen, Ni(0)-Lm = zerovalent nickel complex), (ii) n X-Ar-X + n Me₃Sn-Ar'-SnMe₃ → (Ar-Ar')(n) (palladium catalyzed), and (iii) a X-Ar-X + b X-Ar'-X + (a + b)Ni(0)Lm → (Ar)(x)(Ar')(y). Powder X-ray diffraction analysis confirms an alternative structure of a polymer prepared by the method ii. The copolymers have a molecular weight of 5.4 x 10³ to 3.3 x 10⁵ and an [η] value of 0.37 to 4.4 dL g^-1. π-π* absorption bands of the copolymers generally show red shifts from those of the corresponding homopolymers, (Ar)(n) and (Ar')(n), and the red shifts are accounted for by charge-transferred CT structures of the copolymers. For example, an alternative copolymer of thiophene and 2,3-diphenylquinoxaline gives rise to an absorption band at λ(max) = 603 nm, whereas homopolymers of thiophene and 2,3-diphenylquinoxaline exhibit absorption peaks at about 460 and 440 nm, respectively. The CT copolymers are electrochemically active in both oxidation and reduction regions, showing oxidation (or p-doping) peaks in a range of 0.39 to 1.32 V vs Ag/Ag⁺ and reduction (or n-doping) peaks in a range of -1.80 to -2.22 V vs Ag/Ag⁺, respectively. Copolymers of pyridine give unique cyclic voltammograms exhibiting p-undoping peaks at potentials much different (about 2-3 V lower) from the corresponding p-doping potentials, and this large difference between p-doping and p-undoping potentials is explained by an EC mechanism. They are converted into semiconductors by chemical and electrochemical oxidation and reduction. Copolymers of thiophene with pyridine and quinoxaline show the third-order nonlinear optical susceptibility χ((3)) of about 5 x 10^-11 esu at the three-photon resonant wavelength, which is 5-7 times larger than those of the corresponding homopolymers and related to the CT structure in the copolymers.

Full text of DOI:10.1021/ja961550t

J. Am. Chem. Soc. 1996, 118, 10389-10399
10389
π-Conjugated Donor-Acceptor Copolymers Constituted of
π-Excessive and π-Deficient Arylene Units. Optical and
Electrochemical Properties in Relation to CT Structure of the
Polymer
Takakazu Yamamoto,*,† Zhen-hua Zhou,† Takaki Kanbara,† Masaki Shimura,†
Kenichi Kizu,† Tsukasa Maruyama,† Yoshiyuki Nakamura,† Takashi Fukuda,†
Bang-Lin Lee,† Naoki Ooba,‡ Satoru Tomaru,‡ Takashi Kurihara,‡
Toshikuni Kaino,‡ Kenji Kubota,§ and Shintaro Sasaki|
Contribution from the Research Laboratory of Resources Utilization,
Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226, Japan,
NTT Opto-electronics Laboratories, Nippon Telegraph and Telephone Corporation,
Naka-gun, Ibaraki 319-11, Japan, Fuculty of Engineering, Gunma UniVersity, Tenjincho,
Kiryu 376, Japan, and School of Material Science, Japan AdVanced Institute of Science and
Technology, 1-1 Asahidai, Tatsunokuchi, Ishikawa 923-12, Japan
ReceiVed May 9, 1996X
Abstract: Various π-conjugated copolymers constituted of π-excessive thiophene, selenophene, or furan units
(Ar) and π-deficient pyridine or quinoxaline (Ar′) units have been prepared in high yields by the following
organometallic polycondensation methods: (i) n X-Ar-Ar′-X + n Ni(0)Lm f (-Ar-Ar′)-n (X ) halogen, Ni(0)-
Lm ) zerovalent nickel complex), (ii) n X-Ar-X + n Me3Sn-Ar′-SnMe3 f (-Ar-Ar′-)n (palladium catalyzed),
and (iii) a X-Ar-X + b X-Ar′-X + (a + b)Ni(0)Lm f (-Ar)x(Ar′)-y. Powder X-ray diffraction analysis confirms
an alternative structure of a polymer prepared by the method ii. The copolymers have a molecular weight of 5.4 ×
103 to 3.3 × 105 and an [η] value of 0.37 to 4.4 dL g-1. π-π* absorption bands of the copolymers generally show
red shifts from those of the corresponding homopolymers, (-Ar)-n and (-Ar′)-n, and the red shifts are accounted for by
charge-transferred CT structures of the copolymers. For example, an alternative copolymer of thiophene and 2,3-
diphenylquinoxaline gives rise to an absorption band at λmax ) 603 nm, whereas homopolymers of thiophene and
2,3-diphenylquinoxaline exhibit absorption peaks at about 460 and 440 nm, respectively. The CT copolymers are
electrochemically active in both oxidation and reduction regions, showing oxidation (or p-doping) peaks in a range
of 0.39 to 1.32 V Vs Ag/Ag+ and reduction (or n-doping) peaks in a range of -1.80 to -2.22 V Vs Ag/Ag+,
respectively. Copolymers of pyridine give unique cyclic voltammograms exhibiting p-undoping peaks at potentials
much different (about 2-3 V lower) from the corresponding p-doping potentials, and this large difference between
p-doping and p-undoping potentials is explained by an EC mechanism. They are converted into semiconductors by
chemical and electrochemical oxidation and reduction. Copolymers of thiophene with pyridine and quinoxaline
show the third-order nonlinear optical susceptibility ø(3) of about 5 × 10-11 esu at the three-photon resonant wavelength,
which is 5-7 times larger than those of the corresponding homopolymers and related to the CT structure in the
copolymers.
Introduction
In this papepr, we report preparation of various π-conjugated
polymers with the CT structure and their electrochemical
and optical properties (UV-visible, photoluminescence, and
nonlinear optical properties). This paper deals with the
π-conjugated copolymers constituted of heterocycles. Examples
Chemical and physical properties of charge-transfer (CT)
complexes have attracted strong interest, and a large number
of papers have been published about compounds with the
CT structures.1-3 π-Conjugated polymers have also attracted
strong interest and been the subject of many recent papers.4
Although several papers have recently been published on the
preparation and properties of π-conjugated polymers with the
CT structure,5,6 more detailed studies seem to be required for
revealing their basic properties.
(3) E.g., (a) Priyadarshy, S.; Therien, M. J.; Beratan, D. N. J. Am.
Chem. Soc. 1996, 118, 1504. (b) Maslak, P.; Chopra, A.; Moylan,
C. R.; Wortmann, R.; Lebus, S.; Rheingold, A. L.; Yap, G. P. A. J. Am.
Chem. Soc. 1996, 118, 1471. (c) Roest, M. R.; Verhoeven, J. W.;
Schuddeboom, W.; Warman, J. M.; Lawson, J. M.; Paddon-Row, M. N. J.
Am. Chem. Soc. 1996, 118, 1762. (d) Bryan, C. D.; Cordes, A. W.;
Goddard, J. D.; Haddon, R. C.; Hicks, R. G.; MacKinnon, C. D.;
Mawhinney, R. C.; Oakley, R. T.; Palstra, T. T. M.; Perel, A. S. J. Am.
Chem. Soc. 1996, 118, 330. (e) Fukuzumi, S. AdV. Electron Transf. Chem.
1992, 2, 67.
(4) (a) Skotheim, T. A., Ed. Handbook of Conducting Polymers; Marcel
Dekker: New York, 1986; Vols. I and II. (b) Salaneck, W. R.; Clark, D.
L.; Samuelsen, E. J. E. Science and Applications of Conducting Polymers;
Adam Hilger: New York, 1990. (c) MacDiarmid, A. G.; Heeger, A. J.
NRL Memo. Rep. (Proc. Mol. Electron DeVices Workshop) 1981 AD-A
05816,208. (d) Bradley, D. D. C.; Mori, Y. In Electronic Properties of
Conjugated Polymers III; Kuzmany, H., Mehring, M., Roth, S., Eds.;
Springer: Berlin, 1989.
† Research Laboratory of Resources Utilization, Tokyo Institute of
Technology.
‡ NTT Opto-electronics Laboratories, Nippon Telegraph and Telephone.
§ Gunma University.
| Japan Advanced Institute of Science and Technology.
X Abstract published in AdVance ACS Abstracts, October 1, 1996.
(1) (a) Briegleb, G. Elektronen-Donator Acceptor-Komplexe; Springer:
Berlin, 1961. (b) Foster, F. Organic Charge-transfer Complexes; Academic
Press: New York: 1969.
(2) (a) Mulliken, R. S. J. Am. Chem. Soc. 1950, 72, 600. (b) Mulliken,
R. S. J. Am. Chem. Soc. 1952, 74, 811.
S0002-7863(96)01550-8 CCC: $12.00 © 1996 American Chemical Society

10390 J. Am. Chem. Soc., Vol. 118, No. 43, 1996
Yamamoto et al.
are:
Scheme 1. Order of π-Electron-Donating and -Accepting
Ability of the Monomer Unit
It is established in the chemistry (e.g., in chemical reactivity)
of heterocyclic compounds that five-membered ring heterocycles
such as thiophene and furan have a π-excessive nature whereas
six-membered ring compounds with electron-withdrawing imine
(CdN) nitrogens (e.g., pyridine and quinoxaline) exhibit a
π-deficient nature.7 Actually, the electron-donating and -ac-
cepting ability of the heterocyclic compounds8-12 (and also their
polymers4,13,14) are in the order illustrated in Scheme 1. On
these bases, the copolymers are considered to have CT structures
such as
IP
EA
by using a Stille reaction16 are also used in this research for
investigation of their structure and optical properties. Applica-
tion of the type B polymerization to a new monomer (Ar′ )
2-butyl-3-phenylquinoxaline-5,8-diyl) affords a new copolymer
PThQx(BuPh), and this copolymer is also used (Chart 2).
On the other hand, random type copolymers shown in Chart
3 have been prepared by using the Ni-promoted polyconden-
sation.
The aforementioned polymerizations give the polymers in
high yields (80-100% (Table 1)). Data from elemental analysis
and NMR agree with chemical structures of the polymers
prepared according to eqs 1-3 (cf. the Experimental Section
and supporting information). The composition (m:n) of the
copolymers prepared according to eq 4 roughly agrees with the
feeding ratio of the two monomers (supporting information).
The copolymers reported in this paper are considered to
possess linear molecular structures without branching since
organometallic polymerization methods applied for the prepara-
tion of the copolymers proceed selectively at functional groups
of monomers. Due to the CT and linear structure, the
copolymers are expected to show interesting and unique
chemical and physical properties.
Results and Discussion
IR and NMR. IR spectra of the copolymers give rise to IR
peaks originated from the two aromatic units, Ar and Ar′.
However, ring deformation bands of Ar and Ar′ groups often
show splitting. For example, the ring deformation band of the
pyridine ring of poly(pyridine-2,5-diyl) PPy13a at 1584 cm-1 is
split into two bands at 1592 and 1580 cm-1 in PThPy. Carbon-
Preparation. Polycondensation using a zero valent nickel
complex13,15 gives the copolymers shown in Chart 1 in high
yields as summarized in Table 1. The following previously
reported5d copolymers, PThQx(diph)-PFuQx(diHep), prepared
(5) (a) Zhou, Z.-H.; Maruyama, T.; Kanbara, T.; Ikeda, T.; Ichimura,
K.; Yamamoto, T.; Tokuda, K. J. Chem. Soc., Chem. Commun. 1991, 1210.
(b) Yamamoto, T.; Shimura, M.; Osakada, K.; Kubota, K. Chem. Lett. 1992,
1003. (c) Kurihara, T.; Kaino, T.; Zhou, Z.-H.; Kanbara, T.; Yamamoto,
T. Electron. Lett. 1992, 28, 681. (d) Kanbara, T.; Miyazaki, Y.; Yamamoto,
T. J. Polym. Sci. Part A: Polym. Chem. 1995, 33, 999.
(6) (a) Havinga, E. E.; Ten Hoeve, W.; Wynberg, H. Polym. Bull. (Berlin)
1992, 29, 119. (b) Ferraris, J. P.; Bravo, A.; Kim, W.; Hrncir, D. C. J.
Chem. Soc., Chem. Commun. 1994, 991. (c) Karikomi, M.; Kitamura, C.;
Tanaka, S.; Yamashita, Y. J. Am. Chem. Soc. 1995, 117, 6791.
(7) Newkome, G. R.; Paudler, W. W. Contemporary Heterocyclic
Chemistry; John Wiley: New York, 1982.
(8) (a) Lias, S. A.; Bartmess, J. E.; Holmes, J. L.; Levin, R. D.; Liebman,
J. F.; Mallard, W. G. J. Phys. Chem. Ref. Data Suppl. 1988, 17, 1. (b)
Kagakubenran Kisohen; Jpn. Chem. Soc. Ed.; Maruzen: Tokyo; 1993, II-
620 and II-630. (c) Distefano, G.; Pignatro, S.; Innorta, G.; Fringuelli, F.;
Marioni, G.; Taticchi, A. Chem. Phys. Lett. 1973, 22, 132. (d) Cooper, C.
D.; Williamson, A. D.; Miller, J. C.; Compton, R. N. J. Chem. Phys. 1980,
73, 1527. (e) Johnston, R. A. W.; Melon, F. A. J. Chem. Soc. Faraday
Trans. 2 1973, 69, 1155.
halogen stretching bands of the monomers are not observed in
the IR spectra of the copolymers.
1H-NMR as well as 13C-NMR data of the copolymers shown
above are reasonable for their structures, (cf. the Experimental
Section and supporting information). As shown in Figure 1,
13C{1H}-NMR spectra of symmetrical PPyThPy (chart a) and
PPyPhPy (chart c) show a simple absorption pattern with seven
peaks, respectively, whereas those of PThPy and PPhPy (chart
b) exhibit complicated absorption patterns presumably due to
the presence of both the head-to-tail (HT) and head-to-head
(HH) units. The 13C{1H}-NMR signals of PPyThPy and
PPyPhPy are tentatively assigned as shown in Figure 1 by
comparing the 13C{1H}-NMR data with those of known pyri-
(9) (a) Jordan, K. D.; Burrow, P. D. Acc. Chem. Res. 1978, 11, 341. (b)
Jordan, K. D.; Burrow, P. D. Chem. ReV. 1987, 87, 557. (c) Nenner, I.;
Schulz, G. J. J. Chem. Phys. 1975, 62, 1747. (d) Modelli, A.; Guerra, M.;
Jones, D.; Distefano, G.; Irgolic, K. J., French, K.; Pappalardo, G. C. Chem.
Phys. 1984, 88, 455.
(10) Janousek, B. A.; Brauman, J. I. In Gas Phase Ion Chemistry; Ed.
Bowers, M. T.; Academic Press: New York: 1979; Vol. 2, p 53.
(11) Wiberg, K. B.; Lewis, T. P. J. Am. Chem. Soc. 1970, 92, 7154.
(12) (a) Perichon, J.; Herlem, M.; Bobilliart, F.; Thiebault, A.; Nyberg,
K. Encyclopedia of Electrochemistry of the Element; Bard, A. J., Lund, H.,
Eds.; Marcel Dekker: New York, 1978; Vol. XI, p 2. (b) Baumga¨rtel, H.;
Retzlav, K.-J. Ibid. 1984; Vol. XV, p 167.
(13) (a) Yamamoto, T.; Maruyama, T.; Zhou, Z.-H.; Ito, T.; Fukuda, T.;
Yoneda, Y.; Begum, F.; Ikeda, T.; Sasaki, S.; Takezoe, H.; Fukuda, A.;
Kubota, K. J. Am. Chem. Soc. 1994, 116, 4832. (b) Yamamoto, T.; Morita,
A.; Miyazaki, Y.; Maruyama, T.; Wakayama, H.; Zhou, Z.-H.; Nakamura,
Y.; Kanbara, T.; Sasaki, S.; Kubota, K. Macromolecules 1992, 25, 1214.
(c) Yamamoto, T.; Sugiyama, K.; Kushida, T.; Inoue, T.; Kanbara, T. J.
Am. Chem. Soc. 1996, 118, 3930.
(14) (a) Zotti, G.; Schiavon, G.; Comisso, N.; Berlin, A.; Pagani, G. Synth.
Met. 1990, 36, 337. (b) Wernet, W.; Wegner, G. Makromol. Chem. 1987,
188, 1465. (c) Yamamoto, T.; Wakayama, H.; Fukuda, T.; Kanbara, T. J.
Phys. Chem. 1992, 96, 8677. (d) Diaz, A. F.; Castillo, J. I.; Logan, J. A.;
Lee, W.-Y. J. Electroanal. Chem. 1981, 129, 115. (e) Dian, G.; Barbey,
G.; Decroix, B. Synth. Met. 1986, 13, 281. (f) Yoshino, K.; Kohno, Y.;
Shiraishi, T.; Kaneto, K.; Inoue, S.; Tsukagoshi, K. Synth. Met. 1985, 10,
319. (g) Yamamoto, T. J. Polym. Sci., Part A: Polym. Chem. 1996, 34,
997.
(15) (a) Wang, Y.; Quirk, R. P. Macromolecules 1995, 28, 3495. (b)
Kreyenschmidt, M.; Uckert, F.; Mu¨llen, K. Macromolecules 1995, 28, 4577.
(16) (a) Echavarren, A. M.; Stille, J. K. J. Am. Chem. Soc. 1987, 109,
5478. (b) Bao, Z.; Chan, W.; Yu, L. Chem. Mater. 1993, 5, 2.

π-Conjugated Donor-Acceptor Copolymers
J. Am. Chem. Soc., Vol. 118, No. 43, 1996 10391
Chart 1
Chart 2
of the copolymers under vacuum affords the original polymers
as proved by IR spectroscopy. Although UV-visible absorption
peaks of the copolymers in the acidic solutions show shifts from
those in solvent-free films (Table 1), the results indicate that
the solvent does not form stable salts with the copolymers and
can be removed under vacuum. Sometimes, a small amount of
CF3COOH remained in the polymer sample after the drying
under the vacuum. However, treatment of the sample with NH3-
(aq) followed by drying under vacuum gives solvent-free
original polymer.
Introduction of unsymmetrical substituents in the quinoxaline
13c
unit
as in PThQx(BuPh) (eq 3) renders the polymer some
solubility in nonacidic solvents such as CHCl3 and toluene.
The light scattering measurement reveals that PThPy, PSN13,
and PSN11 have the Fv (degree of depolarization)18 values of
0.09, 0.024, and 0.022, respectively, in formic acid. The Fv
value of PThPy is smaller than that (Fv ) 0.33)13a of rigidly
linear PPy (Vide ante); however, the value of 0.09 is comparable
to that of a stiff poly(aromatic amide), poly(p-benzamide),18c
and suggests PThPy also takes a rather stiff structure in the
solution. The copolymers have large refractive index increments
dine-, thiophene-, and benzene derivatives17 as well as with those
of 2-(R-terthienyl)pyridine Th3R-Py, 3-(R-terthienyl)pyridine
Th3â-Py, and 5,5′-(2-pyridyl)-2,2′-bithiophene R-PyTh2R-Py
prepared in this research.
of ∆n/∆c ) 0.53 - 0.69 cm3 g-1
.
1H-NMR spectra of PFuQx(diHep) and PThQx(BuPh) (charts
a and b in Figure 2) also agree with their structures; splitting of
the butyl signals of PThQx(BuPh) is attributed to the presence
of the HT and HH units with respect to the Qx(BuPh) group.
Molecular Weight, Solubility, and Molecular Structure.
PThPy (run 1 in Table 1) has a molecular weight (mw) of 5400
corresponding to the degree of polymerization of 35, as
determined by a light scattering method.18 A large [η] value
(2.26 dL g-1) of PThPy for its Mw value is attributed to its
stiff structure. PPyThPy (run 9) gives an [η] value of as high
Because of the stiff structure, PThPy molecules in a stretched
poly(vinyl alcohol) (PVA) film exhibit a fairly strong dichroism.
Similar dichroism was reported for rigidly linear PPy.13a The
dichroic ratio Rd13a observed with the PVA-PThPy film (curve
a in Figure 3) is as large as 15 at a stretching ratio Rs of 15;
however, it is smaller than that observed with a PVA-PPy film
(broken line b in Figure 3) due to a less rigid structure of PThPy.
Microstructure and Crystallinity. PThPh, the copolymer
of benzene and thiophene, gives rise to sharp powder X-ray
110, 200, and 210 diffraction peaks at d ) 4.5, 3.9, and 3.1 Å,
respectively. It is known that the p-phenylene Ph unit in poly-
(p-phenylene) PPP19a-c and thiophene-2,5-diyl Th unit in poly-
(thiophene-2,5-diyl)PTh19d,e take almost the same crystallo-
graphic dimensions. The sharp diffraction peaks of PThPh
indicate that it can take a crystalline structure due to the almost
the same crystallographic dimensions of the Ph and Th units,
as 4.4 dL g-1
. In the case of the random copolymers of
thiophene and pyridine (PSN13 and PSN11, runs 16 and 17),
they have a Mw of 5 × 104-3.3 × 105.
The copolymers containing the pyridine unit are generally
soluble in formic acid, whereas the copolymers containing the
quinoxaline unit are soluble in CF3COOH. Drying up solutions
(17) (a) Stothers, J. B. Carbon-13 NMR Spectroscopy; Academic Press:
New York, 1972. (b) Johnson, L. F.; Jankowski, W. C. Carbon-13 NMR
Spectra; John Wiley: New York, 1972.
(18) (a) Kubota, K.; Urabe, H.; Tominaga, Y.; Fujime, S. Macromolecules
1984, 17, 2096. (b) Kubota, K.; Chu, B. Biopolymers 1983, 22, 1461. (c)
Zero, K.; Aharoni, S. M. Macromolecules 1987, 20, 1957. As for Fv, cf.
ref 12a.
(19) (a) Kovacic, P.; Feldman, M. B.; Kovacic, J. P.; Lando, J. B. J.
Appl. Polym. Sci. 1968, 12, 1735. (b) Froyer, G.; Maurice, F.; Mercier, J.
P.; Riviere, D.1 Le Cun, M.; Auvray, P. Polymer 1981, 22, 992. (c) Sasaki,
S.; Yamamoto, T.; Kanbara, T.; Morita, A.; Yamamoto, T. J. Polym. Sci.
1992, 30, 293. (d) Mo, Z.; Lee, K.-B.; Moon, Y. B.; Kobayashi, M.; Heeger,
A. J.; Wudl, F. Macromolecules 1985, 18, 1972. (e) Bru¨ckner, S.; Porzio,
W. Makromol. Chem. 1988, 189, 961.

10392 J. Am. Chem. Soc., Vol. 118, No. 43, 1996
Yamamoto et al.
Chart 3
Table 1. Preparation and Optical Properties of the Donor-Acceptor Copolymersa
absorption,h λmax
,
)
photo-
typec of
polymerization catalystd yielde mol wtf
ligand or
%
[η],g nm (ꢀ, M-1 cm-1
luminescence,i
f
run
monomerb
BrThPyBr
BrThPyBr
BrThPyBr
ClThPyBr
IThPyBr
BrSePyBr
BrPhPyBr
BrThPhBr
BrPyThPyBr
Fv
dL g-1
2.26
in solutionh
film
475j,k
λmax, nm
1
2
3
4
5
6
7
8
9
A(1)
A(1)
A(1)
A(1)
A(1)
A(1)
A(1)
A(1)
A(2)
A(2)
bpy
PPh3
phen
bpy
bpy
bpy
bpy
bpy
bpy
bpy
100 5.4 × 103 0.09
492 (42000)
489
556
100 2.3 × 103
100 2.3 × 103
487
100
96
466
474
477j
485j
562
95
491
95
1.9
382 (35000)
98
85l
100
100
96
4.4
2.8
0.37
0.47
440 (35000)
366 (52000)
605 (5000)
546 (5000)
10 BrPyPhPyBr
384j
603j
580
11 polymer ) PThQx(diPh)4d
12 polymer ) PThQx(diHep)5d
13 polymer ) PFuQx(diPh)5d
14 polymer ) PFuQx(diHep)5d
15 Me3SnTh-SnMe3 +
96
94
692
601
600j
544j
515j
95
B(3)
Pd(PPh3)4
83
0.43
556
634 (721 in film)
BrQx(BuPh)Br
16 BrThBr + BrPyBr ) 1:3
17 BrThBr + BrPyBr ) 1:1
18 BrSeBr + BrPyBr ) 1:4
A(4)
A(4)
A(4)
bpy
bpy
bpy
92 5.1 × 104 0.024 0.92
94 3.3 × 105 0.022
431
407j
441j
376
471
455
428
80
92
1.23
360
ca. 420sh
363
ca. 420sh
ca. 480sh
362
ca. 420sh 517
19 BrSeBr + BrPyBr ) 1:1
A(4)
bpy
430
505
20 BrPhBr + BrPyBr ) 1:1
A(4)
bpy
96
378
a Polymerization conditions: in N,N-dimethylformamide; at 60 °C for runs 1-10 and 15-20, at 85 °C for runs 11-14; for 16-24 h. b The
monomers to give the copolymers shown in eqs 1-4. Th ) thiophene-2,5-diyl. Py ) pyridine-2,5-diyl. Se ) selenophene-2,5-diyl. Ph )
p-phenylene. Qx(diPh) ) 2,3-diphenylquinoxaline-5,8-diyl. Ox(diHep) ) 2,3-diheptylquinoxaline-5,8-diyl. Qx(BuPh) ) 2-butyl-3-phenylqui-
noxaline-5,8-diyl. c Type of polymerization and the number (in the parentheses) of the corresponding equation (cf. text). d Ligand L added in eqs
1, 2, and 4 (bpy ) 2,2′-bipyridyl; PPh3 ) triphenylphosphine; phen ) 1,10-phenanthroline) or catalyst added in eq 3. e Based on carbon recovered.
f Determined by light scattering method. Fv ) degree of depolarization. g Intrinsic viscosity. dL ) 100 mL. Solvent: HCOOH for runs 1, 7, 9,
10, 16, and 18; CCl2COOH for run 15; CF3COOH for runs 11 and 12. At 30 °C. h Solvent: HCOOH for runs 1-10 and 16-20; CF3COOH for
runs 11-14; toluene for run 15. Molecular absorption coefficient (ꢀ). sh ) shoulder peak. i Solvent: the same solvent described in footnote h.
j Film formed on glass substrate by casting. k In PVA film. l Vacuum deposited film on glass substrate.
in spite of containing both the head-to-tail HT and head-to-
head HH units.
of one-dimensional order. The distance of 15.86 Å is assigned
to the following repeating unit in a monoclinic unit cell based
on molecular model and calculation based on the Lennard-
Jones potential. Detailed X-ray structural analysis of PThQx-
To the contrary, a powder X-ray diffraction pattern of PThPy
exhibits only a broad diffraction band due to different crystal-
lographic dimensions between the Th and pyridine-2,5-diyl
units,13a which make it difficult to make microcrystals of PThPy
containing both the HT and HH units.
(diPh) agrees with the assignment and will be reported
elsewhere. Although the copolymerization expressed by eq 3
is believed to give the alternative copolymer, confirmation of
PThQx(diPh) (density ) 1.18 g cm-1) gives sharp powder
X-ray diffraction peaks at d ) 15.86 Å/n (15.86 Å, 7.92 Å,
5.29 Å, and 3.94 Å; n ) 1, 2, 3, 4),20 which indicate the presence
(20) Other peaks are observed at d ) 6.53, 4.70, 4.46, and 3.41 Å.

π-Conjugated Donor-Acceptor Copolymers
J. Am. Chem. Soc., Vol. 118, No. 43, 1996 10393
Figure 2. 1H-NMR spectra of (a) PFuQx(diHep) and (b) PThQx(BuPh)
in trifluoroacetic acid-d.
Figure 1. 13C{1H}-NMR spectra of (a) PPyThPy, (b) PPhPy, and (c)
PPyPhPy in formic acid.
this by X-ray crystallography has no precedent.
Optical and Electrical Properties
UV-Visible Absorption. It may be assumed that the
copolymer shows its π-π* absorption band at a middle position
between the absorption peaks of the corresponding two ho-
mopolymers.
Figure 3. Curve (a): dichroic ratio Rd observed with the lowest energy
π-π* absorption band of PVA-PThPy film. Broken line (b): that of
the PVA-PPy film.13a Definition of the dichroic ratio (Rd) and a
stretching ratio (Rs) was given in ref 13a.
However, a solvent-free film of PThQx(diPh) exhibits a UV-
visible absorption peak at a longer wavelength (λmax ) 603 nm)
than those of films of the corresponding homopolymers PTh
(λmax ) 420-490 nm)21 and poly(2,3-diphenylquinoxaline-5,8-
diyl) PQx(diPh) (λmax ) 444 nm).13c,22 PThQx(diHep), PThPy,
and PSePy also give analogous results. Scheme 2 compares
the λmax values of the related polymers in the state of solvent-
free films (or in CHCl3).
The appearance of the absorption band of the copolymer at
a longer wavelength than the λmax positions of the corresponding
homopolymers suggests formation of a unique electronic state
related to the postulated CT structure of the copolymers.24 The
dichroism observed with the stretched PVA-PThPy film (Vide
ante; Figure 3) indicates that the π-π* absorption of PThPy
has its transition moment essentially along the direction of the
polymer chain.
(21) (a) Yamamoto, T.; Sanechika, K.; Yamamoto, A. Bull. Chem. Soc.
Jpn. 1983, 56, 1497. (b) Tourillon, G. In Handbook of Conducting
Polymers; Skotheim, T. A., Ed.; Marcel Dekker: New York, 1986; Vol. 2,
p 293. (c) Okano, M.; Toda, A.; Mochida, K. Bull. Chem. Soc. Jpn. 1990,
63, 1716. λmax of PTh depends on synthetic methods and conditions for
the measurement. Vacuum-deposited PTh thin film13b exhibits λmax at 410
nm.
PThQx(BuPh) also shows an absorption peak at a longer
wavelength than those of the corresponding homopolymers, PTh
(22) Kanbara, T.; Yamamoto, T. Macromolecules 1993, 26, 3464.

10394 J. Am. Chem. Soc., Vol. 118, No. 43, 1996
Scheme 2. Comparison of λmax of Polymer Films
Yamamoto et al.
(Scheme 2) and poly(2-butyl-3-phenylquinoxaline-5,8-diyl)
PQx(BuPh),13c both in the state of a film and a solution in
toluene.
moves in a direction of the λmax position of PPy (run 9 in Table
1). The random type 1:1 copolymers, PSN11 and PCN11 (eq
4), give the absorption bands near those of PThPy and PPhPy,
respectively. Increase in the pyridine content (PSN13) leads
to shift of the absorption band in the direction of the absorption
band of PPy.
As for low molecular weight organic intermolecular CT
complexes, occurrence of neutral-to-ionic phase transition is
sometimes observed at low temperature as manifested by
changes in their UV-visible spectrum.27,28 However, such a
phase transition has not been observed with the present CT
copolymers (films) in a temperature range of room temperature
through -196 °C.
Photoluminescence. The copolymers of pyridine show
strong photoluminescence both in solutions and films, and peak
positions of the photoluminescence observed in solutions are
shown in Table 1. The peaks of the photoluminescence, except
for that of PSeN type copolymers, appear at onset positions of
their absorption bands, as usually observed with photolumines-
cent aromatic compounds. Excitation spectra of the copolymers
show peaks at the positions of their absorption peaks. These
results indicate that the photoluminescence takes place by
migration of electron in a conduction band (π* level) to a
valence band (π level).
Block Structure of PSeN and Energy Transfer. Among
the PSN and PSeN type copolymers shown in eq 4, PSN type
copolymers seem to have a random sequence whereas the PSeN
type copolymers seem to possess a block type structure, as
judged from their UV-visible and photoluminescence spectra.
PSN11 shows one UV-visible absorption band (chart a in
Figure 4) assigned to a CT absorption band near an absorption
band of PThPy. To the contrary, the PSeN type copolymers
exhibit three UV-visible absorption bands (charts b and c in
Figure 4). Two absorption bands are observed near the
absorption bands of the corresponding homopolymers and one
near the CT band of PSePy (chart d in Figure 4). These results
The peak position of PThQx(BuPh) in the film is shifted
to a longer wavelength, compared with that in toluene, sug-
gesting the presence of interchain CT interaction in the film in
addition to the above discussed intrachain CT interaction.
PThQx(BuPh) shows an [η] value of 0.43 dL g-1 in dichloro-
acetic acid.
UV-visible absorption bands of films of copolymers of furan
also show similar bathochromic shifts from those of the
corresponding homopolymers. λmax of a film of poly(furan-
2,5-diyl)25 appears at 468 nm. On the other hand, the UV-
visible spectra of the CT polymers, PFuQx(diPh) and PFuQx-
(diHep), show the UV-visible absorption peaks at longer
wavelengths, 692 and 601 nm, respectively, in the state of film
(runs 13 and 14 in Table 1).
MNDO calculation of model compounds H(ArAr′)3H and the
aromatic monomer units (HArH and HAr′H) indicates that there
holds roughly linear correlations for both (i) between the
observed π-π* transition energy (Eπ-π*) of the copolymer and
calculated π-π* transition energy of the model compound
H(ArAr′)3H and (ii) between Eπ-π* and energy difference
between LUMO of the electron-accepting heterocyclic com-
pound HAr′H and HOMO of the electron-donating heterocyclic
compound HArH. The correlation ii is associated with the
concept of the CT structure.
A CT structure in a low molecular weight compound, 2-(2′-
thienyl)pyridine (ThPy), which corresponds to the repeating unit
of PThPy, has been proposed on the basis of its chemical
reactivity.26
(24) Insertion of a less bulky five-membered ring unit like thiophene
may release the steric repulsion in the homopolymer of quinoxaline to
contribute to the red shift partly. However, as for pyridine copolymers,
such an effect seems to be minor.
(25) Glenis, S.; Benz, M.; LeGoff, E.; Schindler, J. L.; Kannewurf, C.
R.; Kanatzidis, M. G. J. Am. Chem. Soc. 1993, 115, 12519.
(26) Koffmann, T.; Beissner, G.; Mainbaum, R. Angew. Chem., Int. Ed.
Engl. 1971, 10, 740.
(27) (a) Torrance, J. B.; Vazquez, J. E.; Mayerle, J. J.; Lee, V. Y. Phys.
ReV. Lett. 1981, 46, 253. (b) Torrance, J. B.; Girlando, A.; Mayerle, J. J.;
Crowley, J. I.; Lee, V. Y.; Batail, P. Ibid. 1981, 47, 1747.
(28) Koshihara, S.; Tokura, Y. Kotaibutsuri 1992, 27, 367.
By increasing the fraction of pyridine unit from 1/2 (in the
case of PThPy) to 2/3 (in the case of PPyThPy), the λmax position
(23) A CHCl3-soluble part of PSe prepared by dehalogenation polycon-
densation of 2,5-dibromoselenophene (cf. eq 1) exhibits λmax at 421 nm.
Electrochemically prepared PSe gives λmax at about 440 nm.14f

π-Conjugated Donor-Acceptor Copolymers
J. Am. Chem. Soc., Vol. 118, No. 43, 1996 10395
at various modes, suggests occurrence of an energy transfer (E-
transfer) from the photoactivated PPy unit to the PSe unit. Such
E-transfer has been the subject of recent interest.30 In contrast
to PSeN, PSN gives rise to only one photoluminescence peak
(run 17 in Table 1).
Electrochemical and Chemical Redox (Doping) Reaction.
Figure 5 depicts cyclic voltammograms (CV’s) of a cast PThPy
film on a Pt plate. The CV data reveal the following basic
electrochemical properties of the film.
(a) In the potential range between -2.4 and 0.6 V Vs Ag/
Ag+ (Figure 5a), the CV curve shows four peaks A-D. The
position of peak A corresponds to the oxidation potential of
PTh,4a and the positions of the C-D couple roughly agree with
the doping and undoping potentials of PPy (-2.58 and -2.19
V Vs Ag/Ag+, respectively).13a Color change observed during
the electrochemical redox reaction are shown in Figure 5.
(b) In the range -1.95 to 0.6 V, only the A-B couple is
observed (Figure 5b), whereas scanning in the range -2.4 to 0
V gives rise to only the C-D couple (Figure 5c).
(c) Both the anodic and cathodic peak currents are essentially
proportional to the scanning rate, indicating that the electric
current is determined by the mass of PThPy, and the whole of
PThPy can participate in the redox reaction due to the conductive
properties of the copolymer film.
(d) Use of various electrolytes including [Et4N]X (X ) BF4
or ClO4) and [Bu4N]X (Bu ) butyl; X ) BF4, ClO4 or PF6)
affords essentially the same CV curves. CV data of PThPy
and other polymers are summarized in Table 2.31
Figure 4. UV-visible spectra of (a) PSN11, (b) PSeN14, (c) PSeN11,
and (d) PThPy or PSePy. PThPy and PSePy give the peak at almost
the same position (Table 1). The λmax positions of PPy and PSe are
also shown by bars. Solvent: HCOOH for PSeN, PSN, and PPy; CHCl3
for PSe (soluble part).
Scheme 3. Random Structure of PSN11 and Block Structure
of PSeN
These observations indicate that the A-B couple is mainly
related to the oxidation (p-doping) and reduction (p-undoping)
of thiophene units (eq 5), whereas the C-D couple is mainly
related to the reduction (n-doping) and oxidation (n-undoping),
of the pyridine unit (eq 6). The positive charge and negative
Scheme 4. Energy Transfer in Photoluminescence of PSePy
support the random and block structures of PSN and PSeN,
respectively. The possibility that PSeN contains the homopoly-
mers, PSe and PPy, is excluded, since PSe is insoluble in formic
acid whereas the whole of PSeN14 is soluble in formic acid.
Irradiation of a solution of PSeN with 360 nm light, which
induces absorption by the PPy block,13a causes appearance of
two photoluminescence peaks at positions of light emission from
PPy13a and PSe.29
charge formed according to eqs 5 and 6, respectively, are
delocalized along the polymer chain; however, they are con-
sidered to mainly exist in the thiophene ring and pyridine ring,
respectively. The doping level related to eq 5 is ca. 0.15,
whereas that related to eq 6 is ca. 0.40, as determined from the
electric current.
(30) (a) Watkins, D. M.; Fox, M. A.; J. Am. Chem. Soc. 1994, 116, 6441.
(b) Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.;
Mackay, K.; Friend, R. H.; Burns, P. L.; Holmes, A. B. Nature 1990, 347,
539. (c) Goulle, V.; Harriman, A.; Lehn, J.-M. J. Chem. Soc., Chem.
Commun. 1993, 1034. (d) Okamoto, Y.; Kido, J. Mater. Res. Soc. Symp.
Proc. 1992, 277, 65.
Detailed examination of the photoluminescence (cf. support-
ing information), including measurement of excitation spectra
(29) PSe14f shows a PL peak at 504 nm.

10396 J. Am. Chem. Soc., Vol. 118, No. 43, 1996
Yamamoto et al.
(Table 2). Use of PPyThPy with a higher content of the pyridine
unit affords CV curves similar to those of PThPy, showing larger
peaks originated from the n-doping and n-undoping of the
pyridine unit.
Quinoxaline Copolymers. In contrast to the copolymers of
pyridine, the copolymers of quinoxaline give (a) p-doping and
p-undoping peaks of the thiophene and furan rings and (b)
n-doping and n-undoping peaks of the quinoxaline rings at
normal positions without such large difference between the
p-doping and p-undoping potentials (nos. 9-13 in Table 2).5d
These results indicate that such an EC process observed with
the copolymers of pyridine does not proceed with the p-doping
and p-undoping of the copolymers of quinoxaline.
This distinct difference between the two types of copolymers
may be ascribed to the difference in packing structure between
the two types of polymers, which will affect the ease of the
chemical and/or structural change after the oxidation. Redox
behavior of polymer-modified electrode has been the subject
of recent interest, and many papers have been published.32
The copolymers themselves show low electrical conductivi-
ties. Due to the capability to accept both the p-doping and
n-doping, their electrical conductivity is raised by chemical
doping with iodine (p-doping) and sodium naphthalide (n-
doping). The iodine-doped copolymers exhibit the electrical
conductivity of 6.6 × 10-9 (PSeN14) through 4.2 × 10-2
S
cm-1 (PThPh), whereas the sodium-doped copolymers give the
electrical conductivity of 6.6 × 10-6 (PSeN11) through 1.2 ×
10-3 S cm-1 (PThQx(diPh)).
Electrochemically p-doped PThPy show electrical conductivi-
ties similar to that of the iodine-doped PThPy. The electrical
conductivity of the electrochemically p-doped PThPy exhibits
high stability against time, presumably due to the stability of
p-doped state because of the large difference in the p-doping
and p-undoping potentials. On the other hand, electrochemically
p-doped polyalkylthiophene shows a fairly large time-dependent
decrease in its electrical conductivity.33 The electrical conduc-
tivity of each sample is given in supporting information.
Optical Third-Order Nonlinear Susceptibility ø(3). Pro-
cessable polymer materials with a large ø(3) are considered to
be important materials for rapid switching of light.4 Since it is
known that a narrower band gap of a π-conjugated polymer
brings about a larger ø(3),4 the shift of the π-π* absorption
band to the longer wavelength in the present CT polymers is
expected to contribute to enhancement of the ø(3) value. Figure
6a shows UV-visible and ø(3) spectra of a cast film of PThQx-
(diHep), the latter of which are measured by an optical third
harmonic generation (THG) method. As shown in Figure 6 and
Table 3 (no. 3), PThQx(diHep) film gives maximum ø(3) of
about ø(3)max ) 5 × 10-11 esu at a three-photon resonant region
of the polymer [fundamental wavelength λf(max) ) 1700 nm;
λf(max)/3 ) 567 nm; fundamental wavelength λf ) wavelength
of light irradiated against the sample].
Figure 5. Cyclic voltammograms of a PThPy film (3.8 × 10-8 mol
of monomer unit on a 1 cm × 1 cm Pt electrode in a CH3CN solution
of [Et4N]BF4 (0.1 M). Potential sweep range (Vs Ag/Ag+): (a) -2.4
to 0.6 V; (b) -1.95 to 0.6 V; (c) -2.4 to 0 V.
The unusually large potential difference, ∆E ) Epa - Epc
)
2.1 V, between the A and B peaks of PThPy (eq 5) strongly
suggests the occurrence of chemical and/or structural change
after the oxidation (peak A) of the thiophene ring (EC
mechanism). Since CV charts of 2-(R-terthienyl)pyridine Th3R-
Py, 3-(R-terthienyl)pyridine Th3â-Py, and 5,5′-(2-pyridyl)-2,2′-
bithiophene R-PyTh2R-Py in solutions show normal redox cycles
in both the oxidation and reduction ranges, the unique electro-
chemical behavior is characteristic of the polymer system in
the solid state. Occurrence of a phase transfer due to a change
in Coulombic lattice energy caused by the p-doping and/or
solvation of the p-doped film seems to contribute, at least partly,
to the large difference in the p-doping and p-undoping potentials.
Other copolymers of pyridine exhibit similar CV curves with
such large difference in the p-doping and p-undoping potentials
ø(3)max of π-conjugated molecules usually appears at the three-
photon resonant region, which means that the λf(max)/3 value
corresponds to the position of the π-π* absorption band
contributing to ø(3). Actually, the PThQx(diHep) film gives the
λf(max)/3 agreeing with the λmax of the π-π* absorption (Figure
(31) The A-B couple (Figure 5b) is observable only after the potential
is scanned at least once beyond -2.4 V to give the C-D couple.
(32) E. g., (a) Hilman, A. R. Electrochemical Science and Technology
of Polymers; Linford, R. G., Ed.; Elsevier: New York, 1987. (b) Anson,
F. C.; Blauch, D. N.; Save´ant, J.-M.; Shu, C.-F. J. Am. Chem. Soc. 1991,
113, 1922.
(33) Miyazaki, Y.; Yamamoto, T. Synth. Met. 1994, 64, 69.

π-Conjugated Donor-Acceptor Copolymers
Table 2. CV Data of the Copolymers
J. Am. Chem. Soc., Vol. 118, No. 43, 1996 10397
redox potential, V Vs Ag/Ag+ b
no.
polymer
PThPy
PThPy
PThPy
electrolytea
p-doping (Epa)
p-undoping (Epc)
n-doping (Epc)
n-undoping (Epa)
1
2
3
4
5
6
7
8
9
[Et4N]BF4
[Et4N]ClO4
[Bu4N]BF4
[Et4N]BF4
[Et4N]BF4
[Et4N]BF4
[Et4N]BF4
[Et4N]BF4
[Et4N]BF4
0.39
0.40
0.41
0.5
1.16
0.86
0.66
1.32
0.64
-1.68
-1.69
-1.70
-1.6
-1.97
d
-1.65
-1.94
0.60
-2.20
-2.21
-2.22
-2.1
-2.49
-2.14
-2.24
-2.36
-1.80e
-1.94
-2.14
-2.02
-2.01
-2.02
-1.9
-2.21
d
PSePy
PPhPy
PThPhc
PThBpy
PPhBpy
PThQx(diPh)f
-2.03
-2.11
-1.60
-1.85
-1.90
-2.15e
-1.77
-1.82e
-1.96e
-2.06
-2.01
-1.72
-1.98
-2.03
-1.99
-2.05
-2.06
10
11
12
13
PThQx(diHep)f
PFuQx(diPh)f
PFuQx(diHep)f
PThQx(BuPh)
[Et4N]BF4
[Et4N]BF4
[Et4N]BF4
[Et4N]BF4
0.50
0.50
0.35
0.53
0.35
ca. 0.5g
ca. 0.3g
ca. 0.42
-1.86
-2.08
-2.19
-1.90
-2.09
-2.20
-2.14
-2.23
-2.14
-2.26
14
15
16
17
18
PSN13
PSN11
PSeN14
PSeN11
PCN11
[Bu4N]ClO4
[Bu4N]ClO4
[Et4N]BF4
[Et4N]BF4
[Bu4N]ClO4
0.85f
ca. 0.6
ca. 1.1
0.88
-1.95
-1.94
-1.85e
d
ca. 1.2
-2.00e
a Bu ) butyl. b Peak potentials are shown: Epa ) peak anode potential; Epc ) peak cathode potential. Measured in CH3CN. c Measured with
vacuum-deposited thin film of PThPh on ITO glass electrode due to insolubility of PThPh in solvents. d The CV curve shows clear p-doping and
n-doping peaks; however, the corresponding undoping peak(s) are obscure. e Shoulder peak. f Data from ref 5b. g Broad peak.
6a). PThQx(diPh) and PThPy34 films also give similar ø(3)
spectra exhibiting a peak of the λf(max)/3 value near the π-π*
absorption band.
Table 3 summarizes the ø(3)
values of thin films of the
max
copolymers and homopolymers. As shown in Table 1, PThPy
shows a considerably larger ø(3) value compared with those
max
of PTh and PPy (nos. 1, 6, and 7). PThQx(diPh) and PThQx-
(diHep) give analogous ø(3)
values (nos. 2 and 3).
max
The random copolymers PSN11 and PSN13 give about a half
ø(3) value of PThPy, indicating that the concentration of the
donor-acceptor junction in the copolymer strongly influences
the nonlinear optical properties. In addition, the λf(max)/3
position of the PSN11 film deviates from the λmax position of
its π-π* absorption and appears near the λmax position of PThPy
as shown in Figure 6b. PSN13 film shows the UV-visible
absorption band at a shorter wavelength by 34 nm than that of
PSN11 film (runs 16 and 17 in Table 1); however, the PSN13
film gives the same λf(max) value of 1400 nm or a λf(max)/3
value of 467 nm (nos. 4 and 5 in Table 3). These results indicate
that enhancement of ø(3) for the copolymers of thiophene and
pyridine originates from an electronic state corresponding to
the π-π* absorption at about 470 nm, which is related to the
CT structure in the copolymer. However, revealing the first-
excited and second-excited electronic states of the π-conjugated
polymer will also be important, since a balance of transient
dipole moments between such excited states is also regarded
as an important factor to determine ø(3) as discussed theoreti-
cally.35
Conclusion
Organometallic polycondensations give various π-conjugated
CT copolymers constituted of electron-donating and electron-
(34) We previously reported a ø(3)
However, this value was obtained at a so-called “backside” mode, which
gave a considerably larger ø(3) value than that measured at the mode adopted
in the present study (supporting information).
value of 1.5 × 10-10 esu.5c
max
(35) (a) Guo, D.; Mazumdar, S.; Neher, D.; Stegeman, G. I.; Torruellas,
W. In Organic Materials for Non-linear Optics III; Ashwell, G. J.; Bloor,
D., Eds.; The Royal Society of Chemistry: Cambridge, 1993. (b) Mori,
Y.; Kurihara, T.; Kaino, T.; Tomaru, S. Jpn. J. Appl. Phys. 1992, 31, 896.
Figure 6. UV-visible and ø(3) spectra of (a) PThQx(diHep) film (0.079
µm thickness) and (b) PSN11 film (0.054 µm thickness).

10398 J. Am. Chem. Soc., Vol. 118, No. 43, 1996
Yamamoto et al.
Table 3. Three-Photon Resonant ø(3) Values, ø(3)max, of Thin Films
of π-Conjugated Polymersa
([M-Cl]+, 40, 40), 159 ([M - Br - Cl]+, 70). IR(cm-1): 3048, 1572,
1460, 1431, 1208, 1093, 1006, 830, 793, 738. Anal. Found: C, 39.4;
H, 1.7; N, 5.2; Br+Cl, 41.8; S, 11.4. Calcd for C9H5NBrClS: C, 39.4;
H, 1.8; N, 5.1; Br+Cl, 42.0; S, 11.7%.
no.
polymer
ø(3)max × 1011, esu λf(max), nm λf(max)/3, nm
1
2
3
4
5
6
7
PThPy
4.9
4.5
4.8
2.1
2.5
0.9
0.7d
1500
1700
1700
1400
1400
1700
500
567
567
467
467
567
BrThPyBr. BrThPyBr was prepared according to the following
procedures a and b. Procedure a was similar to the above described
procedure for the preparation of 2-chloro-5-(5-bromo-2-pyridyl)-
thiophene. The product was separated by column chromatography
(silica gel, ether as eluent). Some oligomers and polymer were also
produced and separated from BrThPyBr. Yield of BrThPyBr was 20%.
Mp 111-112 °C. 1H-NMR (CDCl3, ppm): 8.49 (dd, 0.2 Hz and 0.7
Hz, 1H, 6-H at Py-ring), 7.68 (dd, 2.2 Hz and 8.5 Hz, 1H, 4-H at Py-
ring), 7.31 (dd, 8.5 Hz and 0.7 Hz, 1H, 3-H at Py-ring), 7.17 (d, 4.0
Hz, 1H, H at Th-ring), 6.97 (d, 4.0 Hz, 1H, H at Th-ring). 13C-NMR
(CDCl3, ppm): Py-ring, 150.8 (6-C), 150.3 (2-C), 139.4 (4-C), 119.4
(3-C), 118.9 (5-C); Th-ring, 145.3 (5-C), 131.3 (3-C), 125.1 (4-C), 115.9
(2-C). UV-vis (THF): λmax ) 322 nm. Mass (m/e, relative intensity):
321, 319, 317 (M+, 49, 90, 47), 240, 238 ([M - Br]+, 89, 89), 159
([M - 2Br]+, 100). IR(cm-1): 3046, 1571, 1460, 1424, 1208, 1093,
1007, 831, 791, 738. Anal. Found: C, 34.1; H, 1.6; N, 4.4; Br, 49.8;
S, 10.2. Calcd for C9H5NBr2S: C, 33.9; H, 1.6; N, 4.4; Br, 50.1; S,
10.1%.
Procedure b: BrThPyBr was prepared from 2-(5-bromo-2-pyridyl)-
thiophene (Minato, A.; Suzuki, K.; Tamao, K.; Kumada, M. J. Chem.
Soc., Chem. Commun. 1984, 337). 2-(5-Bromo-2-pyridyl)thiophene
(20.23 g, 84.3 mmol) was dissolved in a mixture of acetic acid (150
mL) and chloroform (75 mL), and the solution was cooled to 0 °C in
an ice-water bath. Then, to the solution was added bromine (13.4 g,
84.3 mmol) dissolved in 20 mL of acetic acid very slowly (ca. 3 h).
The mixture was stirred overnight at room temperature, and a large
amount of white solid was separated. The solvent (chloroform) was
removed under reduced pressure, and the residue was poured into 300
mL of ice-water. After filtration and washing with water, the crude
light yellow solid was dried under vacuum and recrystallized from
propanol and chloroform (1:1). Thus, white crystals of BrThPyBr were
obtained (24.7 g, 92%).
PThQx(diPh)
PThQx(diHep)
PSN11
PSN13
PThb,c
PPyb
a Maximum ø(3), ø(3)max, is observed at an irradiated fundamental
wavelength of λf(max). øf(max)/3 is considered to reflect the position
of a π-π* absorption band contributing to ø(3). Measured with cast
film unless otherwise noted. b ø(3) values for PTh and PPy are estimated
from the ø(3) value measured at a so-called backside mode (cf.
supporting information). Corrected ø(3)max values, which are calculated
from relative ø(3) values against that of PThPy (no. 1), are given.
max
c Measured with vacuum-deposited PTh film.13b d Value measured at
3λmax/λf (or hν/Eg)5c ) 0.95.
accepting units. The copolymers exhibit absorption bands at
longer wavelengths than those of the corresponding homopoly-
mers. A copolymer, PSeN, having the block-type structure gives
rise to the energy-transferred photoluminescence. The copoly-
mers are electrochemically active in both the oxidation (p-
doping) and reduction (n-doping) regions, and the copolymers
of pyridine exhibit unique p-doping and p-undoping behavior,
which can be explained by the EC mechanism. Films of PThPy,
PThQx(diPh), and PThQx(diHep) give relatively large ø(3) values
of about 5 × 10-11 esu at their resonant regions, and the
relatively large ø(3) values are considered to be related to the
CT structure.
Experimental Section
Materials. Solvents were dried, distilled, and stored under N2. 2,5-
Dibromopyridine, 1,4-dibromobenzene, 2,5-dibromothiophene, 2,2′-
bipyridine, triphenylphosphine, o-phenanthroline, and 1,5-cycloocta-
diene were purchased from Tokyo Chemical Industry Co. Ltd.
Ni(cod)2,13 Pd(PPh3)4,5d 2,5-dibromoselenophene,36 2,3-diphenyl-5,8-
dibromoquinoxaline,13 2,3-diheptyl-5,8-dibromoquinoxaline,13c and 2-bu-
tyl-3-phenyl-5,8-dibromoquinoxaline13c were prepared as previously
reported. 2,5-Bis(trimethylstannyl)thiophene and 2,5-bis(trimethyl-
stannyl)furan were prepared by modifying a reported method.37
Monomers. XThPyBr (X ) Cl, Br, and I) was prepared as follows.
ClThPyBr. To a suspension of magnesium turnings (0.224 g, 9.2
mmol) in 5 mL of THF was added 2,5-dichlorothiophene (1.408 g, 9.2
mmol) in 10 mL of THF at room temperature dropwise. Then, the
mixture was allowed to stir at room temperature until magnesium
turnings were consumed completely (ca. 4 h). The produced Grignard
reagent was added to a mixture of 2,5-dibromopyridine (2.30 g, 9.7
mmol) and PdCl2(dppb) (0.061 g, 0.10 mmol) suspended in 30 mL of
THF at -30 °C dropwise. After the addition was finished, the mixture
was stirred overnight from -30 °C to room temperature, and it became
a brown homogeneous solution. After THF was removed under reduced
pressure, the residue was added to 100 mL of water. The aqueous
solution was neutralized by dilute hydrochloric acid and then extracted
with benzene (40 mL × 3). The organic layer was washed with water
and dried over sodium sulfate. After filtration and concentration, the
crude product was recrystallized from 1-propanol. Thus, light yellow
crystals were obtained (2,27 g, yield 90%). Mp 108-109 °C. 1H-
NMR (CDCl3, ppm): 8.55 (d, 2.2 Hz, 1H, 6-H at Py-ring), 7.77 (dd,
2.2 Hz and 8.5 Hz, 1H, 4-H at Py-ring), 7.42 (d, 8.55 Hz, 1H, 3-H at
Py-ring), 7.30 (d, 4.0 Hz, 1H, H at Th-ring), 6.90 (d, 8.55 Hz, 1H, 3-H
at Th-ring). 13C-NMR (CDCl3, ppm): Py-ring, 150.5 (6-C), 150.3 (2-
C), 139.2 (4-C), 119.1 (3-C), 118.7 (5-C); Th-ring; 142.2 (5-C), 133.0
(2-C), 127.3 (4-C), 124.1 (3-C). UV-vis (THF): λmax ) 321 nm. Mass
(m/e, relative intensity): 227, 275, 273 (M+, 20, 100, 73), 240, 238
IThPyBr. 2-(5-Bromo-2-pyridyl)thiophene (2.5 g, 10.4 mmol) was
dissolved in 15 mL of dichloromethane. Then, iodine (1.4 g, 0.55
mmol) and 4.2 mL of 6 M nitric acid were added. The mixture was
refluxed for 2.5 h. After cooling to room temperature, the mixture
was poured into an aqueous solution of sodium thiosulfide and extracted
with chloroform (40 mL × 4). The organic layer was dried over sodium
sulfate and decolored by active carbon. After filtration and concentra-
tion, the crude product was recrystallized from acetone to obtain yellow
flake crystal (3.6 g, yield 95%). Mp 124-125 °C. 1H-NMR (CDCl3,
ppm): 8.57 (d, 2.4 Hz, 1H, 6-H at Py-ring), 7.79 (dd, 8.5 Hz and 2.4
Hz, 1H, H at Th-ring), 7.44 (d, 8.5 Hz, 1H, 3-H at Py-ring), 7.25 (d,
3.9 Hz, 1H, 4-H at Py-ring), 7.19 (d, 3.9 Hz, 1H, H at Th-ring). UV-
vis (THF): λmax ) 327 nm. Mass (m/e, relative intensity): 367, 365
(M+, 100, 100), 240, 238 ([M-I]+, 70, 70), 159 ([M - I - Br]+, 60).
IR(cm-1): 3042, 1562, 1448, 1408, 1362, 1093, 1000, 814, 798, 738.
Anal. Found: C, 29.8; H, 1.4; N, 3.9; Br+I, 56.1; S, 8.6. Calcd for
C9H5NBrIS: C, 29.5; H, 1.4; N, 3.8; Br+I, 56.5; S, 8.8%.
Polymerization. Dehalogenation polycondensations using the zero
valent nickel complexes were carried out in manners similar to those
previously reported.13 Copolymers shown in eq 3, except for PThQx-
(BuPh), were prepared as previously reported.5d PThQx(BuPh) was
prepared in an analogus manner.
PThPy. To a solution of bis(1,5-cyclooctadiene)nickel(0) Ni(cod)2
(0.570 g, 2.07 mmol) in 18 mL of dried DMF at room temperature
was added 2,2′-bipyridine (0.322 g, 2.07 mmol). After stirring for 1
h, BrThPyBr (0.510 g, 1.60 mmol) was added at once directly to the
reaction system. The mixture was allowed to react for 28 h at 60-70
°C. After cooling to room temperature, it was added to 100 mL of 2
M HCl and stirred overnight. After filtration, the reddish brown powder
was washed with a mixture of methanol (60 mL) and concd HCl (10
mL), a warm aqueous solution of EDTA (pH ) 9, then pH ) 3), dilute
ammonia, water, and methanol repeatedly, and dried under vacuum
for 20 h at 80 °C to obtain PThPy (run 1 in Table 1) (0.261 g, yield )
ca. 100%). Anal. Found: C, 65.8; H, 3.0; N, 8.2; Br, 1.9. Mw (light
scattering) ) 5400 calcd for H(Py-Th)33Br: C, 66.9; H, 3.1; N, 8.7;
Br, 1.5. Mw ) 5335 calcd for Br(Py-Th)33Br: C, 65.9; H, 3.1; N,
(36) Gronowitz, S.; Frejd, T. Acta Chem. Scand. B 1976, 30, 313.
(37) van Pham, C.; Macomber, R. S.; Mark, H. B., Jr.; Zimmer, H. J.
Org. Chem. 1984, 49, 5250.

π-Conjugated Donor-Acceptor Copolymers
J. Am. Chem. Soc., Vol. 118, No. 43, 1996 10399
8.5; Br, 3.0. Mw ) 5414. IR (cm-1): 1585, 1557, 1525, 1461, 1396,
1384, 1292, 828, 794, 750. 13C-NMR (HCOOH, ppm): 126.0, 129.5,
130.7, 133.3, 133.8, 134.3, 141.0, 143.9, 145.4, 147. CP/MAS 13C-
NMR(ppm): 119.5 (relative peak area (RPA) ) 1), 128 (RPA ) 4.7),
146 (RPA ) 3.6), 152.5 (RPA ) 1.9). PThPy’s prepared analogously
from ClThPyBr and IThPyBr, respectively, showed some differences
in the IR and 13C-NMR spectra. PThPy from ClThPyBr (run 4): IR
(cm-1): 1585, 1558, 1464, 1385, 1333, 1293, 832, 797, 752. 13C-
NMR (HCOOH (50 °C), ppm): 125.1, 128.4, 129.7, 130.7, 132.7,
133.0, 135.0, 138.7, 140.6, 142.4, 143.1, 144.6, 146.2. PThPy from
IThPyBr (run 5): IR (cm-1): 1585, 1558, 1539, 1525, 1461, 1396,
1340, 1291, 1058, 826, 794, 750. 13C-NMR (HCOOH, ppm): 126.1,
126.4, 129.8, 130.9, 131.4, 133.8, 134.3, 140.8, 142.1, 144.1, 145.1,
146.0, 148.7, 149.0.
measurement of the UV-visible spectra at low temperatures.
Thanks are due to Profs. T. Ikeda and K. Osakada of our
laboratory for their helpful discussion.
Supporting Information Available: Synthetic and analytical
data of monomers other than those described in the Experimental
Section, analytical data of polymers other than that described
in the Experimental Section, experimental details of measure-
ments, synthetic data of Th3R-Py, Th3â-Py, and R-PyTh2R-Py,
table of electrical conductivity of the original and doped
polymers, and the photoluminescence spectrum of PSeN14, as
well as IR, NMR, powder X-ray diffraction, and thermogravi-
metric charts of selected polymers (23 pages). These material
is contained in many libraries on microfiche, immediately
follows this article in the microfilm version of the journal, and
can be ordered from the ACS, and can be downloaded from
the Internet; see any current masthead page for ordering
information and Internet access instruction.
PPhPy was prepared in a similar manner. Anal. Found: C, 85.4;
H, 4.8; N, 9.1; Br, 0. Calcd for (C11H7N)n: C, 86.2; H, 4.6; N, 9.1%.
IR (cm-1): 3040, 3010, 1585, 1542, 1457, 815, 754. 13C-NMR
(HCOOH, ppm): 127.3, 129.2, 129.8, 130.6, 132.2, 140.9, 144.0, 146.2,
153.0.
Preparation of other polymers using the Ni(0) complex was carried
out analogously.
Acknowledgment. We are grateful to Professor H. Takezoe
of our university for allowing us to use apparatus for the
JA961550T