Stereocontrolled synthesis and optical properties of all-cis poly(phenylene vinylenes) (PPVs): A method for direct patterning of PPVs

Article abstract of DOI:10.1021/ja042853n

Geometrically pure, all-cis poly(phenylene vinylenes) (PPVs) are synthesized by Suzuki-Miyaura-type polycondensation of 2,5-dioctyloxy-1,4- benzenediboronic acid with (Z,Z)-bis(2-bromoethenyl)benzenes, which are prepared by ruthenium-catalyzed (Z)-selecti

Full text of DOI:10.1021/ja042853n

Published on Web 03/04/2005
Stereocontrolled Synthesis and Optical Properties of All-cis
Poly(phenylene vinylenes) (PPVs): A Method for Direct
Patterning of PPVs
Hiroyuki Katayama,*,† Masato Nagao,† Tatsuro Nishimura,† Yukio Matsui,†
Kazutoshi Umeda,† Kensuke Akamatsu,‡ Takaaki Tsuruoka,‡
Hidemi Nawafune,‡ and Fumiyuki Ozawa*,†
Contribution from the International Research Center for Elements Science (IRCELS), Institute
for Chemical Research, Kyoto UniVersity, Uji, Kyoto 611-0011, Japan, and Faculty of Science
and Engineering, Konan UniVersity, Higashinada-ku, Kobe 658-8501, Japan
Received November 27, 2004; Revised Manuscript Received January 14, 2005; E-mail: hiroyuki@scl.kyoto-u.ac.jp; ozawa@scl.kyoto-u.ac.jp
Abstract: Geometrically pure, all-cis poly(phenylene vinylenes) (PPVs) are synthesized by Suzuki-Miyaura-
type polycondensation of 2,5-dioctyloxy-1,4-benzenediboronic acid with (Z,Z)-bis(2-bromoethenyl)benzenes,
which are prepared by ruthenium-catalyzed (Z)-selective double hydrosilylation of diethynylbenzenes,
followed by bromodesilylation of the resulting (Z,Z)-bis(2-silylethenyl)benzenes with N-bromosuccinimide.
The all-cis PPVs thus obtained undergo one-way photoisomerization to the corresponding trans-PPVs both
in solution and in the solid. This phenomenon is applied to direct microscale patterning of PPVs onto a
quartz substrate.
Poly(phenylene vinylenes) (PPVs) belong to the group of
π-conjugated polymers that have applications in light-emitting
diodes (LEDs),1,2 lasers,3 and solar cells.4 Considerable efforts
have been made to improve their emission color and efficiency
in LEDs by introducing substituents to the polymer skeletons.
On the other hand, although stereoregularity of vinylene linkages
in the polymer backbone is also known to profoundly affect
the optical properties of PPVs,5 efficient ways of regulating the
geometries of vinylene linkages have remained almost unex-
plored. It is particularly difficult to prepare geometrically pure
all-cis PPVs using previous polymerization methods based on
Gilch, Heck, and Wittig reactions.
We recently examined a stereocontrolled synthesis of trans-
and cis-PPVs using Hiyama-type polycondensations of
2,5-dioctyloxy-1,4-diiodobenzene with (E,E)- and (Z,Z)-1,4-
bis(2-silylethenyl)benzenes.6 All-trans PPV was successfully
prepared by this method, but stereoregularity for cis-PPV was
limited to 66%. Herein, we report that all-cis PPVs are
synthesized by Suzuki-Miyaura coupling.7 The resulting poly-
mers exhibit a rather unique photochemical property that allows
the direct microscale patterning of PPVs onto a quartz substrate.
† Kyoto University.
‡ Konan University.
Results and Discussion
(1) (a) Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.;
Mackay, K.; Friend, R. H.; Burn, P. L.; Holmes, A. B. Nature 1990, 347,
539. (b) Burn, P. L.; Holmes, A. B.; Kraft, A.; Bradley, D. D. C.; Brown,
A. R.; Friend, R. H.; Gymer, R. W. Nature 1992, 356, 47. (c) Greenham,
N. C.; Moratti, S. C.; Bradley, D. D. C.; Friend, R. H.; Burn, P. L.; Holmes,
A. B. Nature 1993, 365, 628. (d) Gustafsson, G.; Cao, Y.; Treacy, G. M.;
Klavetter, F.; Colaneri, N.; Heeger, A. J. Nature 1992, 357, 477.
(e) Hoofman, R. J. O. M.; de Haas, M. P.; Siebbeles, L. D. A.; Warman,
J. M. Nature 1998, 392, 54. (f) Welter, S.; Brunner, K.; Hofstraat, J. W.;
De Cola, L. Nature 2003, 421, 54.
(2) For reviews, see: (a) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew.
Chem., Int. Ed. 1998, 37, 402. (b) Friend, R. H.; Gymer, R. W.; Holmes,
A. B.; Burroughes, J. H.; Marks, R. N.; Taliani, C.; Bradley, D. D. C.;
Dos Santos, D. A.; Bre´das, J. L.; Lo¨gdlund, M.; Salaneck, W. R. Nature
1999, 397, 121. (c) Scherf, U. Top. Curr. Chem. 1999, 201, 163. (d)
Akcelrud, L. Prog. Polym. Sci. 2003, 28, 875.
(3) (a) Tessler, N.; Denton, G. J.; Friend, R. H. Nature 1996, 382, 695.
(b) Hide, F.; Diaz-Garcia, M. A.; Schwartz, B. J.; Andersson, M. R.; Pei,
Q.; Heeger, A. J. Science 1996, 273, 1833. (c) McGehee, M. D.; Heeger,
A. J. AdV. Mater. 2000, 12, 1655. (d) Nguyen, T.-Q.; Martini, I. B.; Liu,
J.; Schwartz, B. J. J. Phys. Chem. B 2000, 104, 237.
(4) (a) Yu, G.; Gao, J.; Hummelen, J. C.; Wudl, F.; Heeger, A. J. Science
1995, 270, 1789. (b) Dittmer, J. J.; Petritsch, K.; Marseglia, E. A.; Friend,
R. H.; Rost, H.; Holmes, A. B. Synth. Met. 1999, 102, 879. (c) Gebeyehu,
D.; Brabec, C. J.; Padinger, F.; Fromherz, T.; Hummelen, J. C.; Badt, D.;
Schindler, H.; Sariciftci, N. S. Synth. Met. 2001, 118, 1. (d) Martens, T.;
D’Haen, J.; Munters, T.; Beelen, Z.; Goris, L.; Manca, J.; D’Olieslaeger,
M.; Vanderzande, D.; De Schepper, L.; Andriessen, R. Synth. Met. 2003,
138, 243.
The PPV synthesis was performed with p- and m-isomers of
(Z,Z)-bis(2-bromoethenyl)benzene (4a,b) as monomers, which
were prepared by a two-step procedure given in Scheme 1.8
The first step is (Z)-selective double hydrosilylation of 1,4- and
(5) (a) Son, S.; Dodabalapur, A.; Lovinger, A. J.; Galvin, M. E. Science 1995,
269, 376. (b) Liao, L.; Ding, L.; Karasz, F. E. Pang, Y. J. Polym. Sci.,
Part A: Polym. Chem. 2004, 42, 303. (c) Liao, L.; Pang, Y.; Ding, L.;
Karasz, F. E. Macromolecules 2001, 34, 6756. (d) Pang, Y.; Li, J.; Hu, B.;
Karasz, F. E. Macromolecules 1999, 32, 3946. (e) Sarker, A. M.; Gu¨rel,
E. E.; Ding, L.; Styche, E.; Lahti, P. M.; Karasz, F. E. Synth. Met. 2003,
132, 227. (f) Drury, A.; Maier, S.; Ru¨ther, M.; Blau, W. J. J. Mater. Chem.
2003, 13, 485. (g) Cassano, T.; Tommasi, R.; Babudri, F.; Cardone, A.;
Farinola, G. M.; Naso, F. Synth. Met. 2003, 139, 827. (h) Ronchi, A.;
Cassano, T.; Tommasi, R.; Babudri, F.; Cardone, A.; Farinola, G. M.; Naso,
F. Synth. Met. 2003, 139, 831. (i) Dalton, A. B.; Coleman, J. N.; in het
Panhuis, M.; McCarthy, B.; Drury, A.; Blau, W. J.; Paci, B.; Nunzi, J.-M.;
Byrne, H. J. J. Photochem. Photobiol., A 2001, 144, 31.
(6) Katayama, H.; Nagao, M.; Moriguchi, R.; Ozawa, F. J. Organomet. Chem.
2003, 676, 49.
(7) (a) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457. (b) Miyaura, N.
In Metal-Catalyzed Cross-Coupling Reactions, 2nd ed.; de Meijere, A.,
Diederich, F., Eds.; Wiley-VCH: Weinheim, Germany, 2004; Chapter 2.
(8) Compound 4a has been prepared from 1,4-benzenedicarboxaldehyde in
moderate yield (42%) by a double Wittig reaction: Romero, M. A.; Fallis,
A. G. Tetrahedron Lett. 1994, 35, 4711.
9
4350
J. AM. CHEM. SOC. 2005, 127, 4350-4353
10.1021/ja042853n CCC: $30.25 © 2005 American Chemical Society

Method for Direct Patterning of PPVs
A R T I C L E S
Scheme 1
1,3-diethynylbenzenes (2a,b) with HSiMe2An (An ) 4-meth-
oxyphenyl) to give (Z,Z)-1,4- and (Z,Z)-1,3-bis(2-silylethenyl)-
benzenes (3a,b), respectively. While this reaction was previously
carried out with RuCl2(CO)(PPri3)2 (10 mol %) as a catalyst in
91-92% selectivities,6 it was found that a newly prepared
ruthenium complex 1 bearing an sp2-hybridized phosphorus
ligand (DPCB-OMe)9 serves as a more efficient catalyst with
higher reactivity and selectivity.10-12 Thus, the reaction of 2a
with HSiMe2An (1.9 equiv) in toluene, in the presence of
0.5 mol % of 1, was complete in 1 h at room temperature to
give (Z,Z)-3a in over 99% regio- and stereoselectivities.
Treatment of the product with N-bromosuccinimide (NBS) in
acetonitrile at 0 °C formed (Z,Z)-4a in 65% yield (two steps).13
The m-isomer (Z,Z)-4b was similarly prepared from 2b in 56%
yield. Complex 1 was prepared in 49% yield by treatment of
Ru(η3-allyl)Cl(CO)314 with DPCB-OMe in toluene, followed by
treatment with dry HCl in ether (see Supporting Information).
Polycondensation of (Z,Z)-4a with 1 equiv of 2,5-dioctyloxy-
1,4-benzenediboronic acid (5) was performed in toluene at
80 °C for 24 h in the presence of Pd(PPh3)4 (1.5 mol %), Bu4-
Figure 1. 1H NMR spectra of all-cis 6a (Mn ) 2700) (A), (Z,Z)-7
(B), and all-trans 6a obtained by photoisomerization (C).
NBr (1 equiv), and aqueous K3PO4 (3 equiv). The reaction
solution was then poured into excess MeOH to precipitate an
orange solid of all-cis PPV 6a (Mn ) 4700, PDI ) 1.92, 95%
yield).15 Similarly, all-cis 6b (Mn ) 5100, PDI ) 2.13) was
obtained in 99% yield, starting from (Z,Z)-4b and 5. All
procedures must be performed in the dark to avoid cis-to-trans
isomerization of PPVs (vide infra). The use of KOH instead of
K3PO4 as a base provided comparable results. On the other hand,
the molecular weight of 6a lowered (Mn ) 2700, PDI ) 1.79)
in the absence of Bu4NBr as a phase-transfer catalyst.
An all-cis arrangement of vinylene linkages was confirmed
by NMR spectroscopy. Figure 1 shows the 1H NMR spectrum
of 6a (Mn ) 2700), together with the spectrum of (Z,Z)-2,5-
dioctyloxy-4′-(2-bromoethenyl)stilbene (7), which was prepared
as a minimum model of an all-cis PPV. As already shown by
Pang et al.,5c the signal at δ 3.54 is due to OCH2 protons of
octyloxy groups adjacent to (Z)-vinylene units. On the other
hand, the corresponding signal for the trans-PPV structure
(δ 4.08) was not detected. The small signals observed at
δ 3.95 (a) and 3.65 (b) with the same intensities are assignable
to a 2,5-dioctyloxyphenyl group at a polymer end by comparison
with the spectrum of 7.16 Furthermore, vinylic proton signals
at δ 7.00 (c) and 6.38 (d) are ascribed to the presence of a
BrCHdCH group at the other end of the polymer.
(9) DPCB-OMe ) 1,2-bis(4-methoxyphenyl)-3,4-bis[(2,4,6-tri-tert-butylphe-
nyl)phosphinidene]cyclobutene: Minami, T.; Okamoto, H.; Ikeda, S.;
Tanaka, R.; Ozawa, F.; Yoshifuji, M. Angew. Chem., Int. Ed. 2001, 40,
4501.
(10) The (Z)-selective hydrosilylation of terminal alkynes has been rationalized
by the modified Chalk-Harrod mechanism involving a silylruthenium(II)
complex as a key intermediate,11,12 which may be effectively stabilized by
strong π-accepting ability of DPCB-OMe ligand,9 leading to the high
catalytic reactivity and selectivity.
(11) (a) Seitz, F.; Wrighton, M. S. Angew. Chem., Int. Ed. 1988, 27, 289.
(b) Randolph, C. L.; Wrighton, M. S. J. Am. Chem. Soc. 1986, 108, 3366.
(c) Ferna´ndez, M. J.; Esteruelas, M. A.; Jime´nez, M. S.; Oro, L. A.
Organometallics 1986, 5, 1519. (d) Ojima, I.; Fuchikami, T.; Yatabe, M.
J. Organomet. Chem. 1984, 260, 335. (e) Onopchenko, A.; Sabourin, E.
T.; Beach, D. L. J. Org. Chem. 1983, 48, 5101. (f) Schroeder, M. A.;
Wrighton, M. S. J. Organomet. Chem. 1977, 128, 345.
(12) (a) Maruyama, Y.; Yamamura, K.; Nakayama, I.; Yoshiuchi, K.; Ozawa,
F. J. Am. Chem. Soc. 1998, 120, 1421. (b) Maruyama, Y.; Yamamura, K.;
Sagawa, T.; Katayama, H.; Ozawa, F. Organometallics 2000, 19, 1308.
(c) Katayama, H.; Taniguchi, K.; Kobayashi, M.; Sagawa, T.; Minami, T.;
Ozawa, F. J. Organomet. Chem. 2002, 645, 192.
(13) (a) Tamao, K.; Akita, M.; Maeda, K.; Kumada, M. J. Org. Chem. 1987,
52, 1100. (b) Stamos, D. P.; Taylor, A. G.; Kishi, Y. Tetrahedron Lett.
1996, 37, 8647.
(14) Sbrana, G.; Braca, G.; Piacenti, F.; Pino, P. J. Organomet. Chem. 1968,
13, 240.
All-cis PPVs thus prepared were isomerized to all-trans PPVs
under photoirradiation. Figure 2A shows a change of the
UV-vis spectrum of 6a during the isomerization. When a dilute
solution of all-cis 6a (Mn ) 4700) in benzene was irradiated
(15) GPC data based on polystyrene standards.
(16) 2,5-Dioctyloxyphenyl groups may be generated by hydrolytic deboronation.
9
J. AM. CHEM. SOC. VOL. 127, NO. 12, 2005 4351

A R T I C L E S
Katayama et al.
Figure 3. IR-RAS spectra of a film of all-cis 6a before (solid line) and
after (dotted line) photoirradiation.
Figure 2. Changes of UV-vis absorption spectra of all-cis 6a (Mn ) 4700)
under photoirradiation in benzene (A) and in a film (B).
with a high-pressure Xe lamp (2.1 mW cm-2) at room
temperature, the π-π* transition at 382 nm decreased
rapidly, to be replaced with a strong absorption at 463 nm
(ꢀ ) 38200 M-1 cm-1), which was almost identical to that of
all-trans 6a (Mn ) 5000). The spectroscopic change occurred
within a few minutes, maintaining isosbestic points at 334 and
388 nm. The formation of all-trans 6a was also confirmed by
1H NMR spectroscopy (Figure 1C).6 Thus, the PPV 6a was
found to undergo a clean “one-way” photoisomerization17 from
the all-cis isomer to the all-trans isomer, and this behavior is in
contrast to the reversible isomerization of stilbene- and azoben-
zene-containing polymers.18
Figure 4. Fluorescent images of micropatterned 6a (A) and 6b (B).
atmosphere. The color of the film gradually changed from pale
yellow to orange and became unchanged after 45 min (Figure
2B). The UV-vis spectrum at this stage was consistent with
the formation of trans-PPV, and IR-RAS analysis of the film
supported this conclusion (Figure 3). Interestingly, the PPV film
thus prepared was much less soluble than that before irradiation.
Accordingly, a very simple method for direct patterning of trans-
PPV on a micrometer scale was developed. Thus, UV light was
irradiated for 45 min through a photomask onto a film of all-
cis 6a coated on a quartz plate. The plate was rinsed with CHCl3
to remove those parts of the PPV film that were not irradiated.
Figure 4A shows an optical image of the resulting plate, which
was photographed under UV light. A well-resolved pattern is
observed with yellowish green emission. In a similar procedure,
a micropattern with blue-light emission was developed from
all-cis 6b with m-phenylene units (Figure 4B).
The cis-to-trans isomerization of PPVs also took place in the
solid state. A thin film of all-cis PPV 6a (ca. 90 nm thick),
which was prepared from a CHCl3 solution by spin-coating
on a quartz plate, was irradiated with strong UV light
(35.5 mW cm-2) at room temperature under a nitrogen
(17) Arai, T.; Tokumaru, K. Chem. ReV. 1993, 93, 23.
(18) (a) Momotake, A.; Arai, T. J. Photochem. Photobiol., C 2004, 5, 1.
(b) Macromol. Symp. (Azobenzene-Containing Materials); Natansohn, A.,
Ed.; Wiley-VCH: Weinheim, Germany, 1999; Vol. 139.
9
4352 J. AM. CHEM. SOC. VOL. 127, NO. 12, 2005

Method for Direct Patterning of PPVs
A R T I C L E S
Conclusion
Acknowledgment. We thank Prof. T. Arai (University of
Tsukuba) for helpful discussions. This work was supported by
a Grant-in-Aid for Scientific Research from the Ministry of
Education, Culture, Sports, Science and Technology, Japan.
In conclusion, a highly stereocontrolled synthesis of all-cis
PPVs has been successfully accomplished using the Suzuki-
Miyaura-type polycondensation. (Z,Z)-Bis(2-bromoethenyl)-
benzenes, used as starting monomers, were readily prepared by
using complex 1 bearing an sp2-hybridized phosphorus ligand
as a (Z)-selective double hydrosilylation catalyst for diethynyl-
benzenes. The all-cis PPVs thus prepared undergo one-way
photoisomerization to the corresponding PPVs with (E)-vinylene
linkages under photoirradiation. This property is applicable to
direct patterning of PPVs on a micrometer scale. The method
is extremely simple and should be useful for constructing
functional materials used in optoelectronics.19,20
Supporting Information Available: Experimental details
(PDF). This material is available free of charge via the Internet
at http://pubs.acs.org.
JA042853N
(20) (a) Renak, M. L.; Bazan, G. C.; Roitman, D. AdV. Mater. 1997, 9, 392.
(b) Gigli, G.; Rinaldi, R.; Turco, C.; Visconti, P.; Cingolani, R.; Cacialli,
F. Appl. Phys. Lett. 1998, 73, 3926. (c) DeAro, J. A.; Gupta, R.; Heeger,
A. J.; Buratto, S. K. Synth. Met. 1999, 102, 865. (d) Kobayashi, H.; Kanbe,
S.; Seki, S.; Kigchi, H.; Kimura, M.; Yudasaka, I.; Miyashita, S.; Shimoda,
T.; Towns, C. R.; Burroughes, J. H.; Friend, R. H. Synth. Met. 2000, 111,
125. (e) Liang, Z. Q.; Li, K.; Wang, Q. Langmuir 2003, 19, 5555.
(f) Pogantsch, A.; Trattnig, G.; Zojer, E.; Tillmann, H.; Horhold, H. H.;
Scherf, U.; Langer, G.; Kern, W. Synth. Met. 2003, 138, 85.
(19) For a review, see: Holdcroft, S. AdV. Mater. 2001, 13, 1753.
9
J. AM. CHEM. SOC. VOL. 127, NO. 12, 2005 4353