Alkyne metathesis with simple catalyst systems: Efficient synthesis of conjugated polymers containing vinyl groups in main or side chain

Article abstract of DOI:10.1021/ja0010251

The synthesis of novel conjugated polymers by acyclic diyne metathesis (ADIMET) is reported. These polymers are hybrids between poly(p-phenylenevinylene) and poly(p-phenyleneneethynylene) (PPE). They contain phenylene, ethynylene, and vinylene groups (-≡

Full text of DOI:10.1021/ja0010251

J. Am. Chem. Soc. 2000, 122, 12435-12440
12435
Alkyne Metathesis with Simple Catalyst Systems: Efficient Synthesis
of Conjugated Polymers Containing Vinyl Groups in Main or Side
Chain
Glen Brizius, Neil Gregory Pschirer, Winfried Steffen, Katherine Stitzer,
Hans-Conrad zur Loye, and Uwe H. F. Bunz*
Contribution from the Department of Chemistry and Biochemistry, The UniVersity of South Carolina,
Columbia, South Carolina 29208
ReceiVed March 22, 2000
Abstract: The synthesis of novel conjugated polymers by acyclic diyne metathesis (ADIMET) is reported.
These polymers are hybrids between poly(p-phenylenevinylene) and poly(p-phenyleneneethynylene) (PPE).
They contain phenylene, ethynylene, and vinylene groups (stsPhsdsPhs, PPVE). Simple in situ catalysts
formed from Mo(CO)6 and 4-chlorophenol were used to metathesize the dipropynyl(tetraalkyl)stilbene
monomers. The monomers are made by a combination of Horner reactions and Heck-type couplings. The
PPVEs form in high yields and are structurally defined. They show degrees of polymerization (Pn) of 30-220
repeating units (i.e. 60-450 benzene rings), demonstrating that the presence of the double bonds does not
interfere with alkyne metathesis. The PPVEs were structurally characterized by XRD and electron microscopy.
They show fibrillar and network-type morphologies, which should make them interesting for applications in
molecular electronics. Solid samples of PPVEs display powder XRD patterns almost identical to those of the
PPEs. PPVEs thus assume similar doubly lamellar structures as the PPEs. The aggregation behavior of PPVEs
was studied. In addition, ADIMET to a poly(2,7-fluorenyleneethynylene) carrying unsaturated side chains is
reported. In this case the presence of unsaturation does neither interfer with efficient alkyne metathesis.
Introduction
heterocyclic polymers have certainly played an important role
in these applications8-10 the hugely popular poly(p-phen-
ylenevinylene)s (PPV, 1) and the polyfluorenes dominate the
field of LEDs2 and similar applications, while the poly(p-phen-
yleneethynylene)s (PPE, 2) are increasingly important in diverse
sensing applications.6,7 However, the hybrid of these two
structure types, i.e., PPV and PPE, 3, which could be termed
PPVE, has, surprisingly, never been reported.
We have successfully exploited alkyne metathesis11 with
simple catalyst systems for the preparation of high-molecular-
weight dialkyl-PPEs 212 and polynaphthyleneethynylene-PPE
copolymers13 and in the ring-closing metathesis1 of dipro-
Herein is described the following: (a) “Instant” catalysts
formed from Mo(CO)6 and 4-chlorophenol in off-the-shelf 1,2-
dichlorobenzene perform clean alkyne metathesis of propyny-
lated substrates in the presence of double bonds.1 (b) The
catalysts allow the synthesis of alkyl-substituted poly(p-phe-
nyleneethynylene)/poly(p-phenylenevinylene) hybrids (PPVE,
3) and the preparation of poly(2,7-fluorenyleneethynylene)s (29)
decorated with unsaturated citronellyl side chains. (c) The solid-
state structure, aggregation, and supramolecular ordering of the
PPVEs 3 was determined by powder XRD, electron microscopy,
and UV-vis spectroscopy.
Conjugated polymers are organic semiconductors and as such
are important as active layers in light emitting diodes (LED),2
“plastic” lasers,3 light emitting electrochemical cells,4 thin film
transistors,5 and the growing area of chemical sensing.6,7 While
(6) McQuade, D. T.; Pullen, A. E.; Swager, T. M. Chem. ReV. 2000,
100, 2537. Swager, T. M. Acc. Chem. Res. 1998, 31, 201. Yang, J.-S.;
Swager, T. M. J. Am. Chem. Soc. 1998, 120, 11864.
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(8) Zhang, C. Y.; Tour, J. M. J. Am. Chem. Soc. 1999, 121, 8783. Zhang,
X. J.; Shetty, A. S.; Jenekhe, S. A. Macromolecules 1999, 32, 7422. Zhang,
X. J.; Shetty, A. S.; Jenekhe, S. A. Acta Polym. 1998, 49, 52. Chen, X. L.;
Jenekhe, S. A. Macromolecules 1997, 30, 1728.
(1) (a) Independently of us, Fu¨rstner has recently reported the tolerance
of double bonds in the metathesis of alkynes: Fu¨rstner, A.; Guth, O.;
Rumbo, A.; Seidel G. J. Am. Chem. Soc. 1999, 121, 11108. (b) For related
work of this group see: Fu¨rstner, A.; Seidel, G. Angew. Chem. 1998, 37,
1734. Fu¨rstner, A.; Mathes, C.; Lehmann, C. W. J. Am. Chem. Soc. 1999,
121, 9453. (c) For high yield ring closing alkyne metathesis of 2,n-diyne
hydrocarbons see: Weiss, K. Universita¨t Bayreuth, unpublished results.
(2) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew. Chem. 1998, 37,
402.
(3) (a) Scherf, U. J. Mater. Chem. 1999, 9, 1853. (b) Hide, F.; Diaz-
Garcia, M. A.; Schwartz, B. J.; Heeger, A. J. Acc. Chem. Res. 1997, 30,
430.
(4) Pei, Q.; Yang, Y. J. Am. Chem. Soc. 1996, 118, 7416.
(5) Gonzalez-Ronda, L.; Martin, D. C.; Nanos, J. I.; Politis, J. K.; Curtis,
M. D. Macromolecules 1999, 32, 4558. Nanos, J. I.; Kampf, J. W.; Curtis,
M. D.; Gonzalez, L.; Martin, D. C. Chem. Mater. 1995, 7, 2232. Curtis,
M. D.; Cheng, H.; Nanos, J. I.; Nazri, G.-A. Macromolecules 1998, 31,
205.
(9) (a) Patil, A. O.; Heeger, A. J.; Wudl, F. Chem. ReV. 1988, 88, 183.
(b) Rughooputh, S. D. D. V.; Hotta, S.; Heeger, A. J.; Wudl, F. J. Polym.
Sci., B 1987, 25, 1071. (c) For an excellent overview about polythiophenes
see: Reddinger, J. L.; Reynolds, J. R. AdV. Polym. Sci. 1999, 145, 58.
(10) (a) Lucht, B. L.; Mao, S. S. H.; Tilley, T. D. J. Am. Chem. Soc.
1998, 120, 4354. (b) Mao, S. S. H.; Liu, F. Q.; Tilley, T. D. J. Am. Chem.
Soc. 1998, 120, 1193. (c) Buretea, M. A.; Tilley, T. D. Organometallics
1997, 16, 1507. (d) Nguyen, P.; Gomez-Elipe, P.; Manners, I, Chem. ReV.
1999, 99, 1515 and references cited therein.
(11) Weiss, K.; Michel, A.; Auth, E. M.; Bunz, U. H. F.; Mangel, T.;
Mu¨llen, K. Angew. Chem. 1997, 36, 506. Bunz, U. H. F.; Kloppenburg, L.
Angew. Chem. 1999, 38, 478.
(12) Kloppenburg, L.; Song, D.; Bunz, U. H. F. J. Am. Chem. Soc. 1998,
120, 7973.
(13) Pschirer, N. G.; Vaughn, M. E.; Dong, Y. B.; zur Loye, H. C.; Bunz,
U. H. F. J. Chem. Soc., Chem. Commun. 2000, 85.
10.1021/ja0010251 CCC: $19.00 © 2000 American Chemical Society
Published on Web 12/02/2000

12436 J. Am. Chem. Soc., Vol. 122, No. 50, 2000
Brizius et al.
pynylated phenyl ethers,14 and planned to use ADIMET for the
synthesis of PPVEs 3.
Figure 1. ORTEP of dimer 15.
Results and Discussion
sensitive butadiene group or the limited compatibility of
heterocyclic building blocks such as thiophene to the relatively
harsh metathesis conditions employed here. Side products could
not be identified and starting material was not recovered.
However, this series of experiments shows that alkyne metath-
esis with simple catalyst systems has substantial potential in
small molecule organic chemistry.
Synthesis. At the outset1 of the investigation we were
skeptical if the “instant” catalysts would metathesize propyny-
lated substrates in the presence of double bonds. A series of
propynylated stilbene model compounds 7 (Scheme 1) was
prepared via a combination of organolithium, Heck, and Horner
chemistries. To our pleasant surprise, treatment of 7 with
Mo(CO)6 and 4-chlorophenol under standard metathesis condi-
tions (150 °C, 16-24 h) in off-the-shelf 1,2-dichlorobenzene
(ODCB) furnished the dimers 8b,c and the organometallic
representative 8e. Pure dimers 8 were obtained in almost
quantitative yield after acid and base wash of the reaction
mixture, which was followed by removal of the solvent. Neither
chromatography nor crystallization was necessary for the
purification of these dimers. This result demonstrates that
metathesis of alkynes proceeds smoothly if alkenes are present
in the same molecule. This is remarkable, because the opposite,
i.e., undisturbed olefin metathesis of vinylated, alkyne-contain-
ing substrates, is not common. Instead, alkynes actively
participate and enyne metathesis is observed, as was elegantly
shown by Grubbs and Zuercher.15
With these encouraging results in hand, a series of PPVEs 3
was synthesized. Scheme 2 shows the preparative route to the
monomers 25 and their polymerization to 3. A McMurry
reaction of 6 accessed 25 directly, but in very low yields. Instead
an in situ Horner approach, described by Smith and Salvatore,
was used.16 Reduction of 6 (Scheme 2) with LiAlH4, followed
by in situ reaction with methanesulfonyl chloride and Arbuzov
reaction delivers the phosphonates 24 in good-to-excellent
yields. Horner reaction of 24 with 6 in the presence of an excess
of NaH in dimethoxyethane leads to the monomers 25 in yields
of 70% starting from 6. The use of a Horner reaction, performed
at high temperature in the polar solvent DME, leads to
monomers 25 in which the double bond is solely trans-
1
configured. According to H NMR analysis the trans/cis ratio
These intriguing results prompted us to explore the limits of
tolerance of the simple metathesis catalysts with respect to vinyl
groups. As a consequence we prepared the propynylated
substrates 10, 12, 14, 16, 18, 20, and 22, which we subjected
to the standard metathesis conditions (Scheme 1). To our great
surprise, all of the monomers underwent alkyne metathesis under
standard conditions. Even unsupported styrenes in the meta or
para position (11, 13) are not polymerized but remain untouched
and perform well. Likewise the o-styryl-substituted propynyl
benzene 14 undergoes clean dimerization to 15 in a respectable
84% yield. To prove the structure of the dimer 15 unequivocally,
we performed a single-crystal X-ray study (for details including
packing diagrams see the Supporting Information), which is
shown in Figure 1. The molecule of 15 is Z-shaped and assumes
a fully planar extended conformation in the solid state (see
Supplementary Information). The bond lengths and angles are
in excellent agreement with the expected values.
is >100 in 25a-d. The monomers 25a-d are colorless powders
or almost colorless oils and are subjected to alkyne metathesis
under standard conditions in ODCB at 140-150 °C. The bright
yellow polymers 3a-d are isolated in high yield after acid and
base wash of the reaction mixtures followed by precipitation
into methanol (Scheme 3). Table 1 shows yield, degree of
polymerization (Pn), polydispersity (Mw/Mn), and optical proper-
ties (discussion vide infra) of 3a-d. Both yields and Pn are
substantial for 3 and reinforce that alkyne metathesis with the
instant catalyst is effective in the presence of double bonds.
The polymers 3 were characterized by high-temperature NMR
spectroscopy and their Pn and polydispersity obtained by GPC.
The 1H NMR spectrum of dodecyl-PPVE (3c) shows only three
signals in the aromatic region, assigned to the protons residing
on the trans double bond at δ 7.40 (s, 2 H) and the two different
aromatic protons at δ 7.28 and 7.48 (2s, 2 H each, total of 4
H). In the 13C NMR spectrum of 3c seven signals in the region
of δ 120-145 are observed for the stilbene core and one signal
at δ 92.7 representing the alkyne group.
If butadiene groups or heterocylces are present in the
precursors, the yield of the dimerized diphenylacetylenes (17,
19, and 23) drops to 37-45%, due to either the presence of the
The higher Pn of the polymer 3c when compared to its
congeners 3a,b,d can be explained by the superior purity of
(14) Pschirer, N. G.; Fu, W.; Adams, R. D.; Bunz, U. H. F. J. Chem.
Soc., Chem. Commun. 2000, 87.
(15) Kim, S. H.; Zuercher, W. J.; Bowden, N. B.; Grubbs, R. H. J. Org.
Chem. 1996, 61, 1073. Zuercher, W. J.; Scholl, M.; Grubbs, R. H. J. Org.
Chem. 1998, 63, 4291.
(16) Smith, A. B.; Friestad, G. K.; Barbosa, J.; Bertounesque, E.; Duan,
J. J. W.; Hull, K. G.; Iwashima, M.; Qiu, Y. P.; Spoors, P. G.; Salvatore,
B. A. J. Am. Chem. Soc. 1999, 121, 10478.

Alkyne Metathesis with Simple Catalyst Systems
J. Am. Chem. Soc., Vol. 122, No. 50, 2000 12437
Scheme 1
the corresponding monomer 25c. This monomer was available
on a 2-3 g scale and was multiply recrystallized. The removal
of trace impurities, often hard to detect by NMR, is important
if very high molecular weights are to be obtained in ADIMET.
That is not too surprising, since ADIMET is a polycondensation
process and sensitive to the purity of the utilized monomer. Still,
if only moderately pure monomers are used, PPVEs 3a,b,d of
substantial molecular weights were obtained. This demonstrates

12438 J. Am. Chem. Soc., Vol. 122, No. 50, 2000
Scheme 2. Substituent Pattern of 3, 6, and 24
Brizius et al.
Scheme 3a
a Reagents and conditions: (i) (S)-(+)-citronellyl bromide, BnNMe3+Cl-, DMSO, 18 h, 80%; (ii) propyne, (PPh3)2PdCl2, CuI, piperidine, 16 h,
84%; (iii) Mo(CO)6, 4-chlorophenol, ODCB, 150 °C, 22 h, 89%.
Table 1. Yield, Molecular Weight, Polydispersity, UV/Vis, and Fluorescence of PPVEs 3a-d
Pn
UV/Vis [nm]
fluorescence [nm]
3
substituents
yield (%)
NMR
GPC
Mw/Mn
solution
film
solution
film
a
b
c
3,7-dimethyloctyl
ethylhexyl
dodecyl
78
92
96
98
43
38
152
77
685
100
3.43
2.09
4.29
2.54
405
397
403
399
425, 456 sh
445
419, 460 sh
413, 458 sh
457, 482
458, 485
455, 485
455, 484
481, 514
471, 500
488, 518
496, 513
>150
d
octyl
60
that ADIMET is a sufficiently robust process to furnish PPVEs
in a straightforward manner.
Mo(CO)6 and 4-chlorophenol in off-the-shelf ODCB. This
makes ADIMET a very convenient tool for organic and polymer
synthesis.
Characterization, Optical Behavior, Aggregation, and
Supramolecular Ordering of PPVEs 3. We have recently
investigated aggregation,17 phase behavior,18 and solid-state
structure19 of PPEs (2). PPEs show doubly lamellar liquid
To further explore the tolerance of the metathesis catalysts
for double bonded functionalities, monomer 28 was prepared
according to Scheme 3 and subjected to the conditions of the
alkyne metathesis. Polymer 29 formed in 52% yield (soluble
fraction, some insoluble material) and with a substantial degree
1
(17) (a) Halkyard, C. E.; Rampey, M. E.; Kloppenburg, L.; Studer-
Martinez, S. L.; Bunz, U. H. F. Macromolecules 1998, 31, 8655. (b) Fiesel,
R.; Halkyard, C. E.; Rampey, M. E.; Kloppenburg, L.; Studer-Martinez, S.
L.; Scherf, U.; Bunz, U. H. F. Macromol. Rapid Commun. 1999, 20, 107.
(c) Miteva, T.; Palmer, L.; Kloppenburg, L.; Neher, D.; Bunz, U. H. F.
Macromolecules 2000, 33, 652.
of polymerization (Pn ) 82; Mw/Mn ) 5.3). H and 13C NMR
spectroscopy show that the double bond is intact in 29. From
the results gathered for both the dimers (Scheme 1) as well as
for the polymers 3 and 29 we can conclude that vinylic
functionalities do not interfere with the conditions of alkyne
metathesis when utilizing simple in situ catalysts formed from
(18) Kloppenburg, L.; Claridge, J. B.; zur Loye, H.-C.; Bunz, U. H. F.
Macromolecules 1999, 32, 4460.

Alkyne Metathesis with Simple Catalyst Systems
J. Am. Chem. Soc., Vol. 122, No. 50, 2000 12439
Table 2. X-ray Data of 3a-d (Values for the Corresponding PPEs
Are Given in Parentheses)
3
a
substituents
2Θ (deg)
d (Å)
area percent
3,7-dimethyloctyl
4.149
12.342
20.451
7.002
18.147
20.902
21.144
3.701
11.052
4.351
12.800
21.904
21.3 (21.3)
7.17 (7.2)
4.34
12.6 (12.4)
4.88
4.25 (4.3)
4.20 (4.1)
23.9 (25.0)
8.00 (8.5)
20.3
100.0
7.2
3.5
100.0
17.5
4.1
3.8
100.0
5.3
100.0
9.9
2.2
b
2-ethylhexyl
c
dodecyl
octyl
d
6.91
4.05
increased distances between the polymer chains and thus to
emission which is blue shifted and less disturbed by interchain
interactions. The 3,7-dimethyloctyl substituents in 3a are
moderately effective in this regard, but bisethylhexyl-PPVE 3b
shows a strong blue solid-state emission at 470 nm (Figure 2b).
A second much weaker emission is observed at 500 nm,
suggesting diminished interchain interactions.
In the powder-XRD (see Table 2) of the PPVEs 3 one
diffraction peak at low angles is visible for each of the polymers
3a-d. The low angle diffraction peak has d values from 12.6
(3b) to 23.9 Å for 3c and represents the lateral distance between
chains. Molecular modeling (MM2, Spartan Pro) of an oligo-
meric subunit of 3d shows that the wing span of the side chains
matches this 20.3 Å distance interpreted to be the interchain
distance in 3d. We have recently analyzed the packing behavior
and the solid-state structure of the dialkyl-PPEs 2.19 We find
that the powder X-ray diffraction patterns of 2 and 3 are almost
superimposable, with 2 having better developed and sharper
diffraction peaks. The close match in powder diffraction data
witnesses the structural similarity of 3 to the respective PPEs
2. Vinylene groups can isomorphically substitute alkyne linkages
in an organic solid-state structure. The slight length mismatch
and their out-of-plane rotation (according to MM2 calculations)
to avoid intramolecular steric repulsion does not seem to disrupt
packing. From these data, we conclude that PPVEs 3 form
lamellar phases similar to those observed in the PPEs 2.19,21
High molecular weight PPVEs 3a-d do not melt undecom-
posed according to DSC and variable-temperature polarizing
microscopy data, probably due to the decrease in stability
brought along by the vinylene groups. However, lyotropic liquid
crystalline (LC) phases form as evidenced by polarizing
microscopy. The lyotropic textures observed for 3b are indis-
tinguishable from the textures seen for bisethylhexyl-PPE 2b.18
The notion that side chains critically influence solid-state
structures of rigid rods is supported by the similarity of lyotropic
LC phases of 2 and 3.
Figure 2. (a) UV-vis spectra of polymer 3d in chloroform and after
addition of increasing amounts of methanol. (b) Solid-state emission
spectra of 3a-d (thin films).
crystalline phases,18,19 in which aggregation, phase behavior,
and optical properties go hand in hand.17c It was attractive to
compare the PPVEs 3 to the PPEs 2. How does the presence of
a vinylene group in PPVEs change the optical properties and
the morphology? The solution UV-vis spectra of 3a-d are
broad and unstructured but bathochromically shifted by 11-16
nm when compared to those of identically substituted PPEs.
Upon addition of methanol the PPVEs 3 show the development
of a second, red-shifted transition (460 nm, 3d), which is broad
and featureless (see Figure 2a). This second transition is
attributed to aggregation, induced by the addition of the
nonsolvent methanol. No vibronic fine splitting is observed,
contrary to the case of the PPEs.17 At the moment it is not clear
if the red-shifted aggregate band is due to planarization of the
polymer backbone17c or the formation of ground-state ag-
gregates.20
In solution all PPVEs 3 show emission at 460 nm, with
photoluminescence quantum yields ranging from 28 to 34%.
In the solid state (drop-cast films, slow evaporation) emission
of 3 is dependent on the side chains (Figure 2b, Table 1), with
photoluminescence quantum yields of approximately 5%.
Dodecyl and octyl-PPVE (3c,d) show the most red-shifted,
broad emissions (525 nm), suggesting the formation of solid-
state excimers.20 Substituent branching in 3 probably leads to
Electron microscopy of thin films of 3a,b,d are shown in
Figure 3a-c. Lamellar-fibrillar supramolecular structures form
(3a,d). These are quite similar to structures (nanowebs) observed
by Rabe and Mu¨llen22 and us19b in the self-assembly of dihexyl-
PPEs on mica or graphite. Independently, Swager20b found that
self-assembly of PPEs on the air-water interface gives fibrillar
morphologies. Bisethylhexyl-PPVE 3b on the other hand
displays more of a crystalline, star-shaped morphology (Figure
3b) where several lamellae originate from the same center. These
(19) (a) Bunz, U. H. F.; Enkelmann, V.; Kloppenburg, L.; Jones, D.;
Shimizu, K. D.; Claridge, J. B.; zur Loye, H.-C.; Lieser, G. Chem. Mater.
1999, 11, 1416. (b) Perahia, D.; Traiphol, R.; Bunz, U. H. F. Macromol-
ecules Submitted for publication.
(20) (a) Levitsky, I. A.; Kim, J. S.; Swager, T. M. J. Am. Chem. Soc.
1999, 121, 1466. (b) Kim, J. S.; McHugh, S. K.; Swager, T. M.
Macromolecules 1999, 32, 1500.
(21) The first structural characterization of dialkoxy-PPEs was performed
by Wrighton and Swager. They already suggested the presence of lamellar
phases. (a) Ofer, D.; Swager, T. M.; Wrighton, M. S. Chem. Mater. 1995,
7, 418. For an in-depth discussion of structural models of PPEs see: (b)
Bunz, U. H. F. Chem. ReV. 2000, 100, 1605.

12440 J. Am. Chem. Soc., Vol. 122, No. 50, 2000
Brizius et al.
stars correspond nicely to disclinations found in polarizing
micrographs of the lyotropic LC-preparations of 3b.
In the examined cases of 3 all of the observed fibrils are wire-
like approximately 6-27 nm wide and 80-250 nm long. The
width of the fibrils suggests that the long axes of the PPVE
molecules are arranged along the long axis of the fibril, because
in 3b as well as in 3d the length of a single rigid PPVE chain
considerably extends the width of one lamella. The values
obtained for the width of the lamellae from our fibrous PPVE
networks coincide nicely with the ones found by Rabe, who
interprets these features as fibrillar double ribbons of PPEs.20b,22c
At the same time our PPVE fibrils resemble the lamellar
structures we have recently observed in dialkyl-PPEs 2.20 From
the available evidence the formation of fibrillar-lamellar, wire-
like nanostructures seems a general feature for PPEs, a scheme
into which the related PPVEs 3 fit nicely.
Conclusion
Olefins are noncompetent substrates for alkyne metathesis
catalysts formed from mixtures of Mo(CO)6 and 4-chlorophenol.
On the basis of these finding, two novel types of conjugated
polymers were synthesized, viz. PPVEs 3 and the citronellyl-
substituted poly(fluorenylyeneethynylene)s 14.23 Optical proper-
ties, aggregation behavior, and supramolecular structure/
morphology were examined for 3a-d. While the optical
behavior of 3 is quite different from that of dialkyl-PPEs 2,
their solid-state structure must be isomorphous to that of the
PPEs, according to the powder XRD data. This conclusion is
supported by electron microscopy of thin films of 3 where
formation of fibrous-lamellar structures, closely related to those
observed for PPEs,20,22 was evidenced. We plan to investigate
PPVEs as active layers in light-emitting diodes, organic
semiconductor, and self-assembled nano-devices.
Acknowledgment. We wish to thank the Research Corpora-
tion and the NSF for generous support (CHE 9814118, 1999-
2001). U.H.F.B. is an NSF CAREER awardee (CHE 9981765,
2000-2003) and a Camille Dreyfus Teacher-Scholar (2000-
2004). W.S. thanks Dr. Dana Dunkelberger and Dr. Ute Kolb
(Mainz) for help with the TEM microscopy. We wish to thank
Willi Dindorf (Organisches Institut der Universita¨t Mainz) for
elemental analyses and Dr. Mark Smith for the performance of
the single crystal structure of 15.
Supporting Information Available: Detailed experimental
and procedural details including spectroscopic characterization
for 3-29 and details of the solution of the single-crystal structure
of 15 (PDF). This material is available free of charge via the
Internet at http://pubs.acs.org.
JA0010251
(22) (a) Recently Rabe and Mu¨llen investigated the supramolecular
ordering of PPEs by different microscopy techniques: Samori, P.; Francke,
V.; Mu¨llen, K.; Rabe, J. Thin Solid Films 1998, 336, 13. Samori, P.; Francke,
V.; Mu¨llen, K.; Rabe, J. Chem. Eur. J. 1999, 5, 2313. Samori, P.; Mu¨llen,
K.; Rabe, J. AdV. Mater. 2000, in press. (b) Thu¨nemann, A. F. AdV. Mater.
1999, 11, 127. (c) Schnablegger, H.; Antonietti, M.; Go¨ltner, C.; Hartmann,
J.; Co¨lfen, H.; Samori, P.; Rabe, J.; Ha¨ger, H.; Heitz, W. J. Colloid Interface
Sci. 1999, 212, 24.
Figure 3. Transmission electron micrographs of polymer 3. Films were
obtained by spreading a diluted solution of the respective polymer in
dichloromethane onto a water surface. The films were lifted off by an
immersed copper TEM grid. Scale bars are shown. (a) TEM picture of
3a. (b) TEM picture of 3b. (c) TEM picture of 3d.
(23) For the synthesis of poly[2,7-(9,9-dialkyl)fluorenyleneethynylene]s
see: Pschirer, N. G.; Bunz, U. H. F. Macromolecules 2000, 33, 3961.