Symmetrical Electron-Deficient Materials Incorporating Azaheterocycles

Article abstract of DOI:10.1002/chem.200305073

To investigate the potential of di- and tri-azaheterocycles as building blocks for π-conjugated materials with high electron affinity, linear oligomers incorporating pyrazine and a C₃-symmetric discotic molecule based on triazine were synthesiz

Full text of DOI:10.1002/chem.200305073

FULL PAPER
Symmetrical Electron-Deficient Materials Incorporating Azaheterocycles
Koen Pieterse, Anne Lauritsen, Albertus P. H. J. Schenning,
Jef A. J. M. Vekemans, and E. W. Meijer*[a]
Abstract: To investigate the potential
of di- and tri-azaheterocycles as build-
ing blocks for p-conjugated materials
with high electron affinity, linear
oligomers incorporating pyrazine and a
C3-symmetric discotic molecule based
on triazine were synthesized. The trido-
decyloxyphenyl end-capped ethynylene
pyrazinylene oligomers showed re-
markable solvatochroism in absorption
and emission in solution. The oligom-
ers containing one and two pyrazine
rings displayed liquid crystallinity in
the solid state. The largest ethynylene
pyrazinylene oligomer containing three
pyrazine rings had the lowest first re-
duction potential at ꢀ1.08 V. The tria-
zine-derived discotic molecule exhibit-
ed UV/Vis and fluorescence behavior
comparable to that of the linear
oligomers and featured a first reduc-
tion potential at ꢀ1.49 V, somewhat
lower than expected.
Keywords: conjugation ¥ electron-
deficient compounds
¥
liquid
crystals ¥ nitrogen heterocycles ¥
oligomers
Introduction
could be applied in thin film transistors by means of vapor
deposition. In all these cases fluorine atoms were used to in-
crease the electron deficiency of the p-conjugated system.[9]
Even sexithiophene, normally used as a p-type material, was
transformed into an n-type material in this manner.[10]
In principle, azaheterocycles can be used as the electron-
deficient units in p-conjugated materials. However, to
obtain materials which are stable under ambient conditions,
azaheterocyclic structures must be synthesized with first re-
duction potentials of around ꢀ0.5 V.[11] Although the suita-
bility of azaheterocycles as the basic building blocks for n-
type materials was shown by Yamamoto and co-workers,[12]
the use of azaheterocycles such as pyridine,[13] triazine[14] and
quinoline[15] has only been of limited value in polymer light
emitting diodes. Pyrazine especially has hardly been imple-
mented in electronic devices,[16] which might be the direct
result of difficulties encountered in the synthesis of function-
alized pyrazine monomers and polymers. This is illustrated
by the fact that, to our knowledge, only one polypyrazine
has been described up to now,[17] while reports of pyrazine-
containing copolymers are also scarce.[16,18] The electron-de-
ficient nature of s-triazine has led to the successful use of
this compound as a central acceptor group in the field of
nonlinear optics.[19,20] Recently, we started a program to ex-
plore the potential of azaheterocycles as the electron-defi-
cient building block for n-type materials.[21] We now report
on the synthesis and characterization of well-defined
oligomers containing pyrazine or triazine as azahetero-
cycles.
The application of p-conjugated materials in electronic devi-
ces such as field-effect transistors[1] and light-emitting
diodes[2] has gained much attention over the last two deca-
des. Their ease of modification and good processability po-
tentially help to reduce costs of the devices while on the
other hand the flexibility and, therefore, the applicability of
the devices might be enhanced. Most organic semiconduc-
tors reported so far exhibit p-type characteristics. However,
for the fabrication of real ’plastic electronics’, for example,
bipolar transistors, p-n junction diodes or complementary
circuits, both p-type (electron-rich) and n-type (electron-de-
ficient) materials are needed. For use as the n-type semicon-
ductors in these devices, materials like C60,[3] and naphtha-
lene-1,4,5,8-tetracarboxylic dianhydride[4] have been pro-
posed, but these structures cannot be used in air and are
also sparingly soluble. In fact, it is the environmental sensi-
tivity, low field mobility and difficult synthesis of the n-type
materials which has hampered major progress in this field.[5]
Recently, however, the groups of Bao,[6] Katz,[7] and Friend[8]
described organic n-type semiconductors which were air
stable, showed field mobilities of around 10ꢀ2 cm2 Vꢀ1 sꢀ1 and
[a] Prof. E. W. Meijer, Dr. K. Pieterse, A. Lauritsen,
Dr. A. P. H. J. Schenning, Dr. J. A. J. M. Vekemans
Laboratory of Macromolecular and Organic Chemistry
Eindhoven University of Technology, P.O. Box 513, 5600 MB Eind-
hoven (The Netherlands)
Fax : (+31)40-2451036
E-mail: e.w.meijer@tue.nl
5597
Chem. Eur. J. 2003, 9, 5597 5604
DOI: 10.1002/chem.200305073
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

FULL PAPER
Results and Discussion
(Scheme 1).[19] The latter was prepared in modest yield at
low temperature by the addition of n-butyllithium to a solu-
tion of a 3,4,5-tridodecyloxyphenylacetylene in THF.
The final products were fully characterized by 1H and
13C NMR, UV/Vis, and IR spectroscopy, MALDI-TOF mass
spectrometry, and elemental analysis. 1H NMR spectra of
the obtained oligomers 1, 2 and 3 featured signals of the
pyrazine protons around d=8.8 ppm. The signals at highest
field could be assigned to the protons closest to the elec-
tron-releasing tridodecyloxyphenyl group. Extension of the
oligomers from one to three pyrazine rings, led to a down-
field shift of the protons closest to the center of the mole-
cule due to the electron-withdrawing nature of the pyrazine
rings.
Synthesis: For the synthesis of the pyrazine oligomers, the
ethynylene moiety was introduced as a coupling unit be-
tween the pyrazine rings and end-capped by tridodecyloxy-
phenyl moieties. This should induce liquid crystallinity in
the oligomers and, therefore, can help to organize the mole-
cules in the solid phase. Instead of using the C2-symmetric
pyrazine unit as the electron-deficient building block, s-tria-
zine should also be capable of fulfilling that role. Its C3-sym-
metry leads to the formation of discotic molecules. The
latter generally feature liquid-crystalline mesophases over
broader temperature ranges than their linear analogues of
similar size. However, due to the meta-substitution of the
triazine unit, the effective conjugation length will be limited
to just one branch of the discotic molecule.
Thermotropic properties: To investigate the assumed liquid
crystalline behavior of the oligomers, their melting behavior
was examined by differential scanning calorimetry (DSC)
measurements and polarization microscopy. The smallest
oligomer 1 showed a liquid crystalline mesophase from
13.58C (DH=24 kJmolꢀ1) to 40.18C (DH=13 kJmolꢀ1)
during the second heating run (Figure 1), while the cooling
run was reversible and revealed transitions at 33.98C (DH=
ꢀ10 kJmolꢀ1) and 4.98C (DH=ꢀ16 kJmolꢀ1). Oligomer 2
exhibited two mesophases; the melting peak of the dodecy-
loxy tails was observed at 36.38C (DH=4.9 kJmolꢀ1), while
a transition from one mesophase to another was found at
58.38C (DH=1.0 kJmolꢀ1). Both DSC measurements as
well as polarization microscopy revealed a clearing tempera-
ture of 70.28C (DH=0.9 kJmolꢀ1). The cooling run featured
the same transitions, but the crystallization peak at 14.58C
(DH=ꢀ2.5 kJmolꢀ1) was smaller than its corresponding
melting peak. The latter might mean that 2 cannot crystal-
lize in its preferred orientation, which in turn might explain
the recrystallization peak observed in the heating run. The
mesomorphic behavior exhibited by oligomer 2 is not unusu-
al; molecules with rigid rod-like cores and half-disc shaped
mesogenic endgroups have been shown previously to display
nematic, smectic, cubic and columnar hexagonal mesophas-
es.[25] Therefore, it was even more surprising that oligomer 3
revealed no liquid crystalline behavior at all; it featured
As a first building block the synthesis of a monosubsti-
tuted pyrazine derivative was programmed. The reaction of
equimolar amounts of 2,5-dibromopyrazine and 3,4,5-trido-
decyloxyphenylacetylene (5),[22] using [Pd(PPh3)4] as the cat-
alyst,[23] however, led mainly to the formation of a disubsti-
tuted pyrazine 1 (Scheme 1).
To allow the synthesis of longer oligomers, monosubsti-
tution of the pyrazine unit is a prerequisite. An elegant solu-
tion to this problem would be the preparation of a pyrazine
building block containing two different halogens, since the
latter would also imply a difference in reactivity of the two
substituents. Therefore, 5-bromo-2-iodopyrazine (6) was syn-
thesized by a diazotation reaction starting from 5-bromopyr-
azine-2-amine (Scheme 1). Although initial yields were low,
asymmetric pyrazine 6 could be prepared in 41% yield after
some adaptations of the reaction procedure. Using asym-
metric pyrazine 6 as the starting material and Sonogashira
reaction conditions,[24] monosubstituted pyrazine 7 could,
indeed, be synthesized in high yield and selectivity. After
pyrazine 7 had been allowed to react with trimethylsilylace-
tylene, the trimethylsilyl group of the obtained pyrazine de-
rivative 8 was removed with tetrabutylammonium fluoride.
Even though the deprotection step should be quantitative,
compound 9 was obtained in only 47% yield, presumably
due to degradation of the product during the chromato-
graphic purification. To further elongate the p-conjugated
system and finalize the synthetic route towards oligomer 2,
pyrazine derivative 9 was subsequently coupled to 5-bromo-
2-iodopyrazine, followed by a reaction with 3,4,5-tridodecy-
loxyphenylacetylene to end-cap the oligomer.
To prepare the next oligomer in this series, disubstituted
pyrazine 11 was first synthesized starting from 2,5-dibromo-
pyrazine and trimethylsilylacetylene (Scheme 1). After re-
moval of the trimethylsilyl protecting groups by treatment
with tetrabutylammonium fluoride, 2,5-diethynylpyrazine
(12) was obtained, again only in a moderate yield after puri-
fication by column chromatography. The desired ethynylene
pyrazinylene oligomer could then be synthesized by cou-
pling 12 with two equivalents of bromopyrazine 7, affording
3 in 47% yield.
The discotic molecule 4 was obtained after nucleophilic
substitution of the triazine ring by reaction of cyanuric fluo-
ride with three equivalents of the appropriate acetylide
Figure 1. DSC thermograms of oligomers 1, 2, and 3.
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2003, 9, 5597 5604
5598

Electron-Deficient Materials
5597 5604
Scheme 1. a) [Pd(PPh3)4], KOAc, DMF/toluene, reflux, 2 h; 37%; b) 5-bromopyrazinamine, I2, HI, NaNO2, 08C, 3 h; 41 %; c) 5, [Pd(PPh3)2Cl2], CuI,
Et3N, 20 8C, 2 h; 94%; d) trimethylsilylacetylene, [Pd(PPh3)2Cl2], CuI, Et3N, 60 8C, 45 min; 63%; e) Bu4NF, THF, 208C, 10 min; 47%; f) 6, [Pd(PPh3)2Cl2],
CuI, Et3N, 70 8C, 20 min; 56%; g) 5, [Pd(PPh3)2Cl2], CuI, Et3N, reflux, 1 h; 14%; h) Bu4NF, THF, 208C, 1 min; 50%; i) 7, [Pd(PPh3)2Cl2], CuI, Et3N,
reflux, 2 h; 47%; j) nBuLi, THF, ꢀ788C, cyanuric fluoride, 208C, 2 h; 23%.
5599
Chem. Eur. J. 2003, 9, 5597 5604
www.chemeurj.org
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

E. W. Meijer et al.
FULL PAPER
only a crystalline to isotropic transition at 132.08C (DH=
15 kJmolꢀ1) in the heating run. The latter was confirmed by
polarization microscopy of the isotropic melt, which clearly
showed the growth of crystalline needles upon cooling. Simi-
lar to 2, oligomer 3 only revealed a broad crystallization
peak on the cooling runs and a recrystallization peak
around 908C in the heating runs. The melting behavior of
discotic compound 4 was also investigated by DSC and po-
larization microscopy (Figure 2) and showed a liquid crystal-
line mesophase from 22.98C (DH=32 kJmolꢀ1) to 60.38C
(DH=5.5 kJmolꢀ1) on the heating run. The cooling run was
reversible and featured transitions at 56.68C (DH=ꢀ5.4
kJmolꢀ1) and 16.28C (DH=ꢀ29 kJmolꢀ1). The temperature
range of the liquid crystalline state was similar to the one
observed for oligomer 2, despite the C3 symmetry of 4. The
latter might be a direct result of the shape of the core,
which has only a small p p overlap with neighboring discs.
Although a hexagonal columnar arrangement of the
molecules in the mesophase seems logical, the texture ob-
Figure 3. Circularly integrated X-ray diffraction patterns of neat 4 at dif-
ferent temperatures.
served by polarization microscopy displayed
a
pattern
cence spectra were measured (Table 1). As expected, the
lmax values increased with increasing length of the oligomers,
due to the extension of the p-conjugated system. Bathochro-
mic shifts were observed for all lmax values when the spectra
measured in the polar solvents were compared to those in
hexane, the red shift, however, being larger for the chloro-
form solutions. The lmax values of the excitation spectra
unlike those seen for other discotic molecules. Therefore, a
more in-depth investigation of the liquid crystalline behavior
of discotic molecule 4 was initiated by measuring X-ray dif-
fraction patterns at different temperatures (Figure 3). The
experiments clearly revealed a change in intensity and in
width of the peaks around 558C, which was rationalized by
the transition from the liquid crystalline phase to the iso-
tropic melt. The effect of the melting of the alkoxy tails on
the X-ray diffraction patterns was less pronounced and
could be observed around 158C by the disappearance of the
peak at 10.58. At low temperatures the X-ray diffraction
patterns revealed low intensity signals between 2 and 68
(Figure 3, inset), which could be assigned to higher order re-
flections. Unfortunately, these reflections also disappeared
around 158C and, hence, exact determination of the liquid
crystalline phase was not possible. The thermal stability of 4
was determined by thermal gravimetric analysis (TGA),
which revealed no degradation below 3008C.
Table 1. Spectroscopic data of 1 4.
Compd Solvent
UV/Vis
Excitation
lmax [nmꢀ1
Fluorescence
lmax [nmꢀ1
]
]
lmax [nmꢀ1
]
(e [Lꢀ1 molꢀ1
cmꢀ1])
1
2
3
4
hexane
369 (4.9î104) 384
383 (4.7î104) 389
409
484
472
438
535
536
451
579
579
399
514
chloroform
tetrahydrofuran 376 (4.8î104) 386
hexane
380 (6.6î104) 390
396 (6.0î104) 396
chloroform
tetrahydrofuran 393 (6.4î104) 392
hexane
395 (8.8î104) 391
404 (8.2î104) 400
chloroform
tetrahydrofuran 397 (8.9î104) 396
hexane
chloroform
358 (8.3î104) 358
370 (6.8î104) 373
Optical properties: To determine the optical properties of
the oligomers in solution, UV/Vis, excitation and fluores-
Figure 2. DSC thermogram of star-shaped 4 (left) and the texture of the liquid crystalline mesophase as observed by polarization microscopy at 328C
(right).
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2003, 9, 5597 5604
5600

Electron-Deficient Materials
5597 5604
showed less solvent dependency than those of the UV/Vis
spectra, but the trends displayed by both were comparable.
In contrast to the excitation spectra, the fluorescence
spectra of the oligomers revealed a strong solvent depend-
ency of the lmax values (Table 1). The Stokes shift of the lon-
gest oligomer 3 tripled, going from the hexane to the THF
solution (Figure 4). The intensity of the emission bands was
also directly related to the polarity of the solvent and
showed a decrease with increasing polarity. Again, the stron-
gest effects were observed for oligomer 3 (Table 1). The
strong solvent dependency of the Stokes shift as well as the
fluorescence intensity could point to the occurrence of a
twisted intramolecular charge transfer (TICT) state. The
latter has been observed previously for other donor accept-
or substituted ethynylene derivatives[26] and is due to the in-
terconversion from a locally excited to a charge transfer
state, facilitated by rotation about a bond. The charge trans-
fer state, which is stabilized by polar solvents, could in our
case lead to energy dissipation by nonradiative pathways
and thus explain the difference in fluorescence intensity be-
tween solutions of the oligomers in polar and apolar sol-
vents.
nm (Table 1, Figure 5), respectively, and were similar to
those found for smallest linear oligomer 1. The latter is in
agreement with the limited p-conjugation in discotic com-
pound 4 as a consequence of the meta-substitution of the tri-
azine unit.
Fluorescence spectroscopy revealed the same solvent de-
pendent emission behavior as observed for the linear
oligomers, showing an increase of the Stokes shift and a de-
crease in emission intensity with increasing solvent polarity
(Figure 5). Moreover, in contrast to the linear oligomers, the
lmax values of the excitation spectra of 4 also exhibited
strong solvent dependency.
Electrochemistry: To test the electron-withdrawing proper-
ties, the first reduction potentials of the synthesized
oligoꢀmers were determined by cyclic voltammetry (Figure
6). Oligomers 1, 2 and 3 showed quasi-reversible first reduc-
tion potentials (Epc) at ꢀ1.68, ꢀ1.38 and ꢀ1.08 V, respective-
ly. In addition, oligomer 3 could be quasi-reversibly reduced
a second time at ꢀ1.31 V, while all oligomers could be re-
duced once more below ꢀ2.3 V, but these reductions were
not reversible.
UV/Vis spectra of discotic molecule 4 in hexane and
chloroform solutions featured lmax values of 358 nm and 370
Since discotic compound 4 has limited p-conjugation, a
first reduction potential similar to the one obtained for
oligomer 1 (ꢀ1.68 V) was expected; however, a first reduc-
tion potential of ꢀ1.49 V was measured by CV. The latter is
obviously due to the higher electron affinity of the triazine
unit compared to pyrazine. Although multiple CV scans of 4
showed no change in signal intensity, the cyclic voltammo-
gram of the latter showed no oxidation wave and was thus
deemed irreversible. A second reduction, which was found
at ꢀ2.08 V, revealed the same electrochemical behavior.
Conclusion
A discotic molecule incorporating triazine and oligomeric
structures incorporating pyrazine were synthesized. Since
direct coupling of the pyrazine rings proved to be difficult,
ethynylene groups were introduced as coupling units. The
latter did not diminish the stability or negatively influence
Figure 4. Excitation and fluorescence spectra of oligomer 3 in various sol-
vents.
Figure 5. Excitation and fluorescence spectra of 4 in hexane and chloro-
form.
Figure 6. Cyclic voltammograms of ethynylene pyrazinylene oligomers 1,
2 and 3 (conditions: tetrahydrofuran, 0.1m Bu4NPF6, SCE, 100 mVsꢀ1).
5601
Chem. Eur. J. 2003, 9, 5597 5604
www.chemeurj.org
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

E. W. Meijer et al.
FULL PAPER
5-Bromo-2-iodopyrazine (6): In a 100 mL three-necked flask equipped
with a mechanical stirrer, 5-bromopyrazinamine[28] (2.0 g, 11.5 mmol) was
suspended in hydroiodic acid (57% in water, 7.4 mL), which was cooled
using an ice-salt bath. I2 (2.0 g, 7.8 mmol) was slowly added, keeping the
temperature of the mixture below 28C, followed by the addition of
NaNO2 (3.31 g, 48.0 mmol) over a period of 3 h. The mixture was made
alkaline by first adding a Na2S2O5 solution (10% in water, 50 mL) and
then a saturated Na2CO3 solution (30 mL). The obtained mixture was ex-
tracted with diethyl ether (3î80 mL) and the organic layer was subse-
quently washed with a Na2S2O5 solution (10% in water, 100 mL), dried
over MgSO4, filtered and evaporated to dryness. Purification of the resi-
due by column chromatography (SiO2, diethyl ether (25%) in hexane,
Rf =0.7) afforded pure 6 as a white solid (1.34 g, 4.70 mmol, 41%). 1H
NMR (CDCl3): d=8.61 (d, J=1.4 Hz, 1H; H-3), 8.50 ppm (d, J=1.4 Hz,
1H; H-6); 13C NMR (CDCl3): d=152.8 (C-3), 148.6 (C-6), 140.5 (C-5),
115.0 ppm (C-2).
the electronic properties of the oligomers. Although none of
the obtained structures showed a first reduction potential as
low as ꢀ0.5 V, they demonstrate the value of azaheterocy-
cles in the design and synthesis of electron-deficient materi-
als. The evolution of the first reduction potentials of the
ethynylene pyrazinylene series from ꢀ1.68 to ꢀ1.08 V (n=
1!3), suggests that with nꢁ6 the target value can be ap-
proached. The liquid crystalline or crystalline behavior ex-
hibited by the tridodecyloxyphenyl substituted compounds
might be used as a tool to organize the molecules on a nano-
scopic level and, thus, enhance their properties in organic-
based electronic devices.
2-Bromo-5-(3,4,5-tridodecyloxyphenylethynyl)pyrazine (7): 5-Bromo-2-
iodopyrazine (6, 0.43 g, 1.51 mmol) and 3,4,5-tridodecyloxyphenylacety-
lene[22] (0.98 g, 1.50 mmol) were dissolved in triethylamine (10 mL) and
the catalysts [Pd(PPh3)2Cl2] (0.0127 g, 0.0181 mmol, 1 mol%) and CuI
(0.0088 g, 0.046 mmol, 3 mol%) were added. The mixture was stirred at
room temperature for 2 h, evaporated to dryness, dissolved in toluene
and again evaporated to dryness to remove any residual triethylamine.
Purification by column chromatography (SiO2, hexane (40%) in di-
chloromethane, Rf =0.3) yielded 7 as a yellow-orange waxy solid (1.14 g,
1.40 mmol, 94%). 1H NMR (CDCl3): d=8.65 (d, J=1.5 Hz, 1H; H-6),
8.48 (d, J=1.5 Hz, 1H; H-3), 6.81 (s, 2H; HPh-2,6), 3.97 (m, 6H; OCH2),
1.84 1.72 (m, 6H; OCH2CH2), 1.46 (m, 6H; OCH2CH2CH2), 1.26 (m,
48H; (CH2)8), 0.88 ppm (t, J=7.0 Hz, 9H; CH3); 13C NMR (CDCl3): d=
153.3 (CPh-3,5), 147.4, 147.3 (C-3,6), 140.6 (CPh-4), 138.9, 138.8 (C-2,5),
115.6 (CPh-1), 110.9 (CPh-2,6), 95.7 (CPzꢀCꢂC-CPh), 84.0 (CPzꢀCꢂC-CPh),
73.8 (CPh-4-OCH2), 69.4 (CPh-3,5-OCH2), 32.2, 30.5, 30.0, 29.9, 29.9, 29.8,
29.6, 29.5, 26.3, 22.9 ((CH2)10), 14.3 ppm (CH3).
Experimental Section
General: All solvents used were p.a. quality. Tetrahydrofuran (THF) was
distilled over Na/K/benzophenone, while triethylamine was dried over
KOH. For column chromatography Merck silica gel 60 was used or
Merck alumina 90 (activity II-III), while for preparative size exclusion
1
chromatography Bio-Rad S-X1 Beads were used. H and 13C NMR spec-
tra were recorded on a Varian Gemini spectrometer with frequencies of
300.1 and 75.0 MHz, respectively, an AM-400 Bruker spectrometer with
frequencies of 400.1 and 100.6 MHz, respectively, or a Varian Mercury
spectrometer with frequencies of 400.1 and 100.6 MHz, respectively.
Chemical shifts are given in ppm (d) downfield from tetramethylsilane
(TMS). UV/Vis spectra were recorded on a Perkin Elmer Lambda 3B
spectrophotometer, a Perkin Elmer Lambda 40P spectrophotometer or a
Perkin Elmer Lambda 900 UV/Vis/NIR spectrophotometer. Fluorescence
spectra were recorded on a Perkin Elmer LS50B luminescence spectrom-
eter and infrared spectra on a Perkin-Elmer Spectrum One using an atte-
nuated total reflection (ATR) sample accessory. The optical properties
and melting points were determined using a Jenaval polarization micro-
scope equipped with a Linkam THMS 600 heating device. DSC data was
collected on a Perkin Elmer Pyris 1 under a nitrogen atmosphere, while
TGA data was collected on a Perkin Elmer TGA 7. Mass spectra were
recorded on a Perseptive DE Voyager MALDI-TOF spectrometer utiliz-
ing a-cyano-4-hydroxycinnamic acid as the matrix. Elemental analysis
was performed on a Perkin Elmer 2400 series analyzer. Cyclic voltammo-
grams were obtained in THF with 0.1m tetrabutylammonium hexafluoro-
phosphate as supporting electrolyte using a Potentioscan Wenking POS73
potentiostat. A platinum disk (diameter 5 mm) was used as working elec-
trode, the counter electrode was a platinum plate (5î5 mm2) and a satu-
rated calomel electrode (SCE) was used as reference electrode.
5-(3,4,5-Tridodecyloxyphenylethynyl)-2-trimethylsilylethynylpyrazine (8):
2-Bromo-5-(3,4,5-tridodecyloxyphenylacetylene)pyrazine (7, 0.5 g, 0.62
mmol) was dissolved in triethylamine (3.5 mL) and trimethylsilylacety-
lene (0.09 mL, 0.64 mmol) was added. After addition of [Pd(PPh3)2Cl2]
(0.0448 g, 0.0064 mmol, 1 mol%) and CuI (0.0037 g, 0.0192 mmol,
3
mol%), the reaction mixture was heated at 608C for 45 min, allowed to
cool and filtered. The filter was washed with triethylamine and the com-
bined filtrates were evaporated to dryness. Purification of the crude ma-
terial by column chromatography (SiO2, heptane (40%) in dichlorome-
thane) afforded 8 as a dark colored solid (0.32 g, 0.39 mmol, 63%). 1H
NMR (CDCl3): d=8.66 (d, J=1.5 Hz, 1H; H-3), 8.64 (d, J=1.5 Hz, 1H;
H-6), 6.81 (s, 2H; HPh-2,6), 4.00 3.95 (m, 6H; OCH2), 1.82 1.72 (m, 6H;
OCH2CH2), 1.46 (m, 6H; OCH2CH2CH2), 1.26 (m, 48H; (CH2)8), 0.88 (t,
J=6.8 Hz, 9H; CH3), 0.29 ppm (s, 9H; Si(CH3)3); 13C NMR (CDCl3):
d=153.3 (CPh-3,5), 147.5, 147.0 (C-3,6), 140.6 (CPh-4), 138.5, 137.2 (C-
2,5), 115.7 (CPh-1), 110.9 (CPh-2,6), 101.9 (CPzꢀCꢂC-Si), 101.0 (CPzꢀCꢂC-
Si), 96.3 (CPzꢀCꢂC-CPh), 85.2 (CPzꢀCꢂC-CPh), 73.8 (CPh-4-OCH2), 69.4
(CPh-3,5-OCH2), 32.2, 31.8, 30.5, 29.9, 29.9, 29.9, 29.9, 29.8, 29.6, 29.5,
26.3, 22.9 ((CH2)10), 14.3 (CH3), ꢀ0.2 ppm (Si(CH3)3).
2,5-Bis(3,4,5-tridodecyloxyphenylethynyl)pyrazine (1): 2,5-Dibromopyra-
zine[27] (0.367 g, 1.50 mmol) and 3,4,5-tridodecyloxyphenylacetylene[22]
(0.993 g, 1.50 mmol) were dissolved in a mixture of DMF (4 mL) and tol-
uene (4 mL). To this mixture KOAc (0.234 g, 2.25 mmol) and [Pd(PPh3)4]
(70 mg, 0.060 mmol, 4 mol%) were added under an argon atmosphere
and subsequently the heterogeneous mixture was heated under reflux for
2 h. Toluene was removed in vacuo and the DMF suspension was poured
into a mixture of diethyl ether (50 mL), and aqueous 0.25m HCl (25 mL).
After separation, the organic layer was washed with another portion of
aqueous 0.25m HCl (25 mL) and evaporated to dryness. The residue was
purified by column chromatography (SiO2, dichloromethane (30%) in
heptane), yielding 1 as an off-white solid (0.380 g, 0.274 mmol, 37%). 1H
NMR (CDCl3): d=8.70 (s, 2H; H-3,6), 6.83 (s, 4H; HPh-2,6), 3.99 (m,
12H; OCH2), 1.83 1.69 (m, 12H; OCH2CH2), 1.47 (m, 12H;
OCH2CH2CH2), 1.26 (m, 96H; (CH2)8), 0.88 ppm (t, J=6.8 Hz, 18H;
CH3); 13C NMR (CDCl3): d=153.3 (CPh-3,5), 147.2 (C-3,6), 140.5 (CPh-4),
137.9 (C-2,5), 115.8 (CPh-1), 110.9 (CPh-2,6), 96.1 (CPzꢀCꢂC-CPh), 85.3
(CPzꢀCꢂC-CPh), 73.8 (CPh-4-OCH2), 69.4 (CPh-3,5-OCH2), 32.2, 30.6, 30.0,
29.9, 29.9, 29.9, 29.8, 29.6, 29.5, 26.3, 22.9 ((CH2)10), 14.3 ppm (CH3); IR
5-Ethynyl-2-(3,4,5-tridodecyloxyphenylethynyl)pyrazine (9): Pyrazine de-
rivative 8 (0.72 g, 0.87 mmol) was dissolved in THF (5 mL) and Bu4NF
(1m in THF, 1.50 mL, 1.50 mmol) was added. The solution was stirred at
room temperature for 10 min and then filtered over a short silica column
using dichloromethane as the eluent. The filtrate was evaporated to dry-
ness and the crude oil was purified by column chromatography (SiO2,
hexane (33%) in dichloromethane, Rf =0.46), yielding pure 9 as a yellow
1
solid (0.31 g, 0.41 mmol, 47%). H NMR (CDCl3): d=8.66 (d, J=1.5 Hz,
1H; H-6), 8.64 (d, J=1.5 Hz, 1H; H-3), 6.81 (s, 2H; HPh-2,6), 3.98 3.94
(m, 6H; OCH2), 3.43 (s, 1H; CꢂCꢀH), 1.82 1.72 (m, 6H; OCH2CH2),
1.45 (m, 6H; OCH2CH2CH2), 1.25 (m, 48H; (CH2)8), 0.86 ppm (t, J=6.8
Hz, 9H; CH3); 13C NMR (CDCl3): d=153.3 (CPh-3,5), 147.6, 147.1 (C-
3,6), 140.7 (CPh-4), 139.1 (C-2), 136.6 (C-5), 115.6 (CPh-1), 110.9 (CPh-2,6),
96.5 (CPzꢀCꢂCꢀCPh), 85.1 (CPzꢀCꢂCꢀCPh), 82.8 (CPzꢀCꢂCꢀH), 80.3 (CPzꢀ
CꢂCꢀH), 73.8 (CPh-4-OCH2), 69.4 (CPh-3,5-OCH2), 32.2, 30.5, 30.0, 29.9,
29.9, 29.8, 29.6, 29.5, 26.3, 22.9 ((CH2)10), 14.3 ppm (CH3).
~
(ATR): n=2917, 2849, 2213, 1573, 1505, 1467, 1422, 1385, 1360, 1300,
1267, 1233, 1121, 1028, 1011, 991, 970, 910, 826, 721 cmꢀ1; MALDI-TOF
M S [M+H+]: calcd 1387.2 Da; found 1387.0 Da; elemental analysis calcd
(%) for C92H156N2O6 (1386.26): C 79.71, H 11.34, N 2.02; found: C 79.80,
H 11.24, N 2.01.
2-(5-Bromo-2-pyrazinylethynyl)-5-(3,4,5-tridodecyloxyphenylethynyl)pyr-
azine (10): Pyrazine derivative 9 (0.165 g, 0.22 mmol) and 5-bromo-2-io-
dopyrazine (6, 0.0693 g, 0.24 mmol) were dissolved in triethylamine (2
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2003, 9, 5597 5604
5602

Electron-Deficient Materials
5597 5604
mL) and [Pd(PPh3)2Cl2] (0.0015 g, 0.0022 mmol, 1 mol%) and CuI
(0.0013 g, 0.0066 mmol, 1 mol%) were added. The reaction mixture was
heated at 708C for 20 min, allowed to cool and filtered. The filter was
washed with triethylamine and the combined filtrates were then evapo-
rated to dryness. Purification by column chromatography (SiO2, dichloro-
methane) afforded 10 as a yellow solid (0.1126 g, 0.123 mmol, 56%). 1H
NMR (CDCl3): d=8.82 (s, 1H; H-3), 8.75 (s, 1H; H-3’/6), 8.74 (s, 1H; H-
3’/6), 8.62 (s, 1H; H-6’), 6.86 (s, 2H; HPh-2,6), 4.01 3.97 (m, 6H; OCH2),
1.83 1.72 (m, 6H; OCH2CH2), 1.48 (m, 6H; OCH2CH2CH2), 1.27 (m,
48H; (CH2)8), 0.88 ppm (t, J=6.8 Hz, 9H; CH3); 13C NMR (CDCl3): d=
153.4 (CPh-3,5), 148.0, 147.8, 147.6, 147.4 (C-3,3’,6,6’), 140.9, 140.8 (C-2,
8.82 (d, J=1.1 Hz, 2H; H-3’), 8.75 (d, J=1.1 Hz, 2H; H-6’), 6.83 (s, 4H;
HPh-2,6), 3.99 3.96 (m, 12H; OCH2), 1.83 1.75 (m, 12H; OCH2CH2),
1.46 (m, 12H; OCH2CH2CH2), 1.25 (m, 96H; (CH2)8), 0.87 ppm (t, J=
7.0 Hz, 18H; CH3); 13C NMR (CDCl3): d=153.3 (CPh-3,5), 148.2 (C-3,6),
147.9 (C-3’), 147.5 (C-6’), 140.8 (CPh-4), 139.6 (C-5’), 137.7 (C-2,5), 135.9
(C-2’), 115.5 (CPh-1), 111.1 (CPh-2,6), 97.5 (CPz’ꢀCꢂC-CPh), 91.4 (CPzꢀCꢂ
CꢀCPz’), 90.2 (CPzꢀCꢂCꢀCPz’), 85.3 (CPz’ꢀCꢂCꢀCPh), 73.8 (CPh-4ꢀOCH2),
69.4 (CPh-3,5-OCH2), 32.2, 30.6, 29.9, 29.9, 29.6, 29.5, 26.3, 22.9 ((CH2)10),
~
14.3 ppm (CH3); IR (ATR): n=2920, 2851, 2206, 1572, 1499, 1467, 1420,
1358, 1298, 1262, 1233, 1188, 1151, 1114, 1030, 916, 833, 767, 721 cmꢀ1
;
MALDI-TOF MS [M+H+]: calcd 1591.5 Da; found 1592.5 Da; elemental
analysis calcd (%) for C104H160N6O6 (1590.45): C 78.54, H 10.14, N 5.28;
found: C 78.25, H 10.06, N 4.94.
C
Ph-4), 139.7, 137.3, 136.0 (C-2’,5,5’), 115.6 (CPh-1), 111.1 (CPh-2,6), 97.5
(CPzꢀCꢂCꢀCPh), 90.3 (CPzꢀCꢂCꢀCPz’), 89.3 (CPzꢀCꢂCꢀCPz’), 85.4 (CPzꢀCꢂ
CꢀCPh), 73.9 (CPh-4-OCH2), 69.5 (CPh-3,5-OCH2), 32.3, 30.7, 30.0, 30.0,
29.9, 29.7, 29.6, 29.4, 26.4, 23.0 ((CH2)10), 14.4 ppm (CH3).
2,4,6-Tris(3,4,5-tridodecyloxyphenylethynyl)triazine (4): Blanketed by
argon, nBuLi (1.6m in hexane, 2.35 mL, 3.76 mmol) was added dropwise
to a stirred solution of 3,4,5-tridodecyloxyphenylacetylene (2.47 g, 3.77
mmol) in THF (10 mL) at ꢀ788C.[19] The solution was stirred for 1 h, al-
lowed to warm to room temperature and stirred for another 20 min. The
solution was then cooled to ꢀ788C and a solution of cyanuric fluoride
(0.146 g, 1. 08 mmol) in THF (1 mL) was added dropwise. The mixture
was warmed to room temperature, stirred for 2 h, and water (10 mL) and
dichloromethane (10 mL) were added. The layers were separated and the
aqueous layer was extracted with dichloromethane (2î10 mL). The com-
bined organic layers were then washed with brine, dried over Na2SO4, fil-
tered and evaporated to dryness. The residue was purified by column
chromatography (SiO2, pentane (25%) in dichloromethane) and prepara-
tive size exclusion chromatography (Biobeads, CH2Cl2), affording pure 4
as a yellow waxy solid (0.51 g, 0.25 mmol, 23%). 1H NMR (CDCl3): d=
6.92 (s, 6H; HPh-2,6), 4.03 3.94 (m, 18H; OCH2), 1.85 1.70 (m, 18H;
OCH2CH2), 1.48 (m, 18H; OCH2CH2CH2), 1.27 (m, 144H; (CH2)8), 0.87
ppm (t, J=5.9 Hz, 27H; CH3); 13C NMR (CDCl3): d=160.7 (C-2,4,6),
153.3 (CPh-3,5), 141.6 (CPh-4), 114.5 (CPh-1), 112.0 (CPh-2,6), 95.2 (CTzꢀCꢂ
C-CPh), 86.2 (CTzꢀCꢂCꢀCPh), 73.9 (CPh-4-OCH2), 69.4 (CPh-3,5-OCH2),
32.2, 31.9, 30.6, 30.0, 29.9, 29.8, 29.7, 29.5, 26.3, 23.0 ((CH2)10), 14.3 ppm
1,2-Bis[2-{5-(3,4,5-tridodecyloxyphenylethynyl)pyrazinyl}]ethyne (2): Pyr-
azine derivative 10 (0.1102 g, 0.12 mmol) and 3,4,5-tridodecyloxyphenyla-
cetylene (0.082 g, 0.12 mmol) were dissolved in triethylamine (3.3 mL)
and [Pd(PPh3)2Cl2] (0.0008 g, 0.0012 mmol, 1 mol%) and CuI (0.0007 g,
0.0036 mmol, 1 mol%) were added. The reaction mixture was then
heated under reflux for 1 h, allowed to cool and evaporated to dryness.
The residue was dissolved in diethyl ether (10 mL), washed with water
(2î10 mL), dried over MgSO4 and again evaporated to dryness. Pure 2
was obtained as a yellow solid (0.0257 g, 0.017 mmol, 14%), after two pu-
rifications by column chromatography (SiO2, dichloromethane, Rf =0.44).
1H NMR (CDCl3): d=8.82 (d, J=1.5 Hz, 2H; H-3), 8.75 (d, J=1.5 Hz,
2H; H-6), 6.84 (s, 4H; HPh-2,6), 4.02 3.96 (m, 12H; OCH2), 1.83 1.74
(m, 12H; OCH2CH2), 1.47 (m, 12H; OCH2CH2CH2), 1.26 (m, 96H;
(CH2)8), 0.88 ppm (t, J=6.8 Hz, 18H; CH3); 13C NMR (CDCl3): d=153.3
(CPh-3,5), 147.9 (C-3), 147.4 (C-6), 140.8 (CPh-4), 139.5 (C-5), 136.1 (C-2),
115.6 (CPh-1), 111.0 (CPh-2,6), 97.3 (CPzꢀCꢂCꢀCPh), 90.6 (CPzꢀCꢂCꢀCPz),
85.3 (CPzꢀCꢂCꢀCPh), 73.8 (CPh-4-OCH2), 69.4 (CPh-3,5-OCH2), 32.2, 30.5,
30.0, 29.9, 29.9, 29.9, 29.8, 29.6, 29.5, 26.3, 22.9 ((CH2)10), 14.3 ppm
~
(CH3); IR (ATR): n=2918, 2850, 2207, 1572, 1500, 1467, 1420, 1360,
~
(CH3); IR (ATR): n=2920, 2852, 2218, 1575, 1492, 1468, 1421, 1377,
1298, 1261, 1234, 1149, 1113, 1029, 1011, 912, 801, 721 cmꢀ1. MALDI-
1306, 1236, 1168, 1115, 1052, 1002, 830, 819, 721 cmꢀ1; MALDI-TOF MS
[M+H+]: calcd 2041.8 Da; found 2042.1 Da; elemental analysis calcd
(%) for C135H231N3O9 (2040.33): C 79.47, H 11.41, N 2.06; found: C 79.53,
H 11.32, N 2.06.
TOF MS [M+H+]: calcd 1489.4 Da; found 1490.4 Da.
2,5-Bis(trimethylsilylethynyl)pyrazine (11): 2,5-Dibromopyrazine[27] (1.55
g, 6.5 mmol) was dissolved in triethylamine (26 mL) and trimethylsilyla-
cetylene (1.85 mL, 13 mmol) was added. Then, the catalysts
[Pd(PPh3)2Cl2] (0.0844 g, 0.07 mmol 0.5 mol%) and CuI (0.0284 g, 0.15
mmol, 1 mol%) were added. The mixture was heated under reflux for 1
h, allowed to cool and filtered. The filter was then carefully washed with
triethylamine and the combined filtrates were evaporated to dryness. Pu-
rification by column chromatography (SiO2, dichloromethane (33%) in
heptane, Rf =0.25) afforded 11 as a white solid (0.66 g, 2.4 mmol, 37%).
1H NMR (CDCl3): d=8.60 (s, 2H; H-3), 0.28 ppm (s, 18H; Si(CH3)3);
13C NMR (CDCl3): d=147.4 (C-3,6), 137.8 (C-2,5), 102.2, 100.8 (CꢂC),
ꢀ0.2 ppm (Si(CH3)3).
[1] A. R. Brown, A. Pomp, C. M. Hart, D. M. de Leeuw, Science 1995,
270, 972.
[2] a) A. Kraft, A. C. Grimsdale, A. B. Holmes, Angew. Chem. 1998,
110, 416; Angew. Chem. Int. Ed. 1998, 37, 402; b) R. H. Friend, R.
W. Gymer, A. B. Holmes, J. H. Burroughes, R. N. Marks, C. Taliani,
D. D. C. Bradley, D. A. Dos Santos, J.-L. Brÿdas, M. Lˆgdlund, W.
R. Salaneck, Nature 1999, 397, 121.
[3] R. C. Haddon, A. S. Perel, R. C. Morris, T. T. M. Palstra, A. F.
Hebard, R. M. Fleming, Appl. Phys. Lett. 1995, 67, 121.
[4] J. G. Laquindanum, H. E. Katz, A. Dodabalapur, A. J. Lovinger, J.
Am. Chem. Soc. 1996, 118, 11331.
[5] F. W¸rthner, Angew. Chem. 2001, 113, 1069; Angew. Chem. Int. Ed.
2001, 40, 1037.
[6] a) Z. Bao, A. J. Lovinger, J. Brown, J. Am. Chem. Soc. 1998, 120,
207; b) J. H. Schˆn, C. Kloc, Z. Bao, B. Batlogg, Adv. Mater. 2000,
12, 1539.
[7] a) H. E. Katz, A. J. Lovinger, J. Johnson, C. Kloc, T. Siegrist, W. Li,
Y. -Y. Lin, A. Dodabalapur, Nature 2000, 404, 478; b) H. E. Katz, J.
Johnson, A. J. Lovinger, W. Li, J. Am. Chem. Soc. 2000, 122, 7787.
[8] A. Facchetti, Y. Deng, A. Wang, Y. Koide, H. Sirringhaus, T. J.
Marks, R. H. Friend, Angew. Chem. 2000, 112, 4721; Angew. Chem.
Int. Ed. 2000, 39, 4547.
[9] Perylenetetracarboxyldiimides are already n-type materials without
incorporation of fluorine atoms. For a recent example see C. W.
Struijk, A. B. Sieval, J. E. J. Dakhorst, M. van Dijk, P. Kimkes, R. B.
M. Koehorst, H. Donker, T. J. Schaafsma, S. J. Picken, A. M. van de
Craats, J. M. Warman, H. Zuilhof, E. J. R. Sudhˆlter, J. Am. Chem.
Soc. 2000, 122, 11057.
2,5-Diethynylpyrazine (12): 2,5-Bis(trimethylsilylethynyl)pyrazine (11,
1.06 g, 3.89 mmol) was dissolved in THF (20 mL) and Bu4NF (1m in
THF, 8.0 mL, 8.0 mmol) was added. The reaction mixture was stirred for
1 min, poured into diethyl ether (50 mL) and washed with water (2î50
mL). The organic phase was then dried over MgSO4, filtered and evapo-
rated to dryness. Purification by column chromatography (SiO2, diethyl
ether (25%) in pentane) afforded 12 as a yellow-white solid (0.25 g, 1.98
1
mmol, 50%). H NMR (CDCl3): d=8.64 (s, 2H; H-3,6), 3.44 ppm (s, 2H;
CꢂCꢀH); 13C NMR (CDCl3): d=147.6 (C-3,6), 137.8 (C-2,5), 83.3 (CPzꢀ
CꢂCꢀH), 80.1 ppm (CPzꢀCꢂCꢀH).
Note: Since diethynylpyrazine 12 is rather volatile, evaporation of the
solvents should be done at room temperature to prevent sublimation.
2,5-Bis[5-(3,4,5-tridodecyloxyphenylethynyl)-pyrazinylethynyl]pyrazine
(3): 2,5-Diethynylpyrazine (12, 0.03 g, 0.24 mmol) and 2-bromo-5-(3,4,5-
tridodecyloxyphenylethynyl)pyrazine (7, 0.3727 g, 0.46 mmol) were dis-
solved in triethylamine (2 mL) and spatula ends of Pd(PPh3)2Cl2 and CuI
were added. The reaction mixture was heated under reflux for 2 h, blan-
keted by argon, allowed to cool and filtered. The filter was washed with
triethylamine and the combined filtrates were evaporated to dryness. Pu-
rification of the crude material by column chromatography (SiO2, ethyl
acetate (1%) in dichloromethane) yielded pure 3 as a yellow waxy solid
(0.1803 g, 0.114 mmol, 47%). 1H NMR (CDCl3): d=8.87 (s, 2H; H-3,6),
[10] A. Facchetti, M. Mushrush, H. E. Katz, T. J. Marks, Adv. Mater.
2003, 15, 33.
5603
Chem. Eur. J. 2003, 9, 5597 5604
www.chemeurj.org
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

E. W. Meijer et al.
FULL PAPER
[11] D. M. de Leeuw, M. M. J. Simenon, A. R. Brown, R. E. F. Einer-
hand, Synth. Met. 1997, 87, 53.
[20] S. Brasselet, F. Cherioux, P. Audebert, J. Zyss, Chem. Mater. 1999,
11, 1915.
[21] a) K. Pieterse, J. A. J. M. Vekemans, H. Kooijman, A. L. Spek, E. W.
Meijer, Chem. Eur. J. 2000, 6, 4597; b) K. Pieterse, P. A. van Hal, R.
Kleppinger, J. A. J. M. Vekemans, R. A. J. Janssen, E. W. Meijer,
Chem. Mater. 2001, 13, 2675.
[22] A. P. H. J. Schenning, M. Fransen, E. W. Meijer, Macromol. Rapid
Commun. 2002, 23, 266.
[23] Y. Akita, H. Kanekawa, T. Kawasaki, I. Shiratori, A. Ohta, J. Heter-
ocycl. Chem. 1988, 25, 975.
[24] K. Sonogashira, Y. Tohda, N. Hagihara, Tetrahedron Lett. 1975,
4467.
[25] a) H. -T. Nguyen, C. Destrade, J. MalthÜte, Adv. Mater. 1997, 9, 375;
b) K. E. Rowe, D. W. Bruce, J. Mater. Chem. 1998, 8, 331.
[26] L. R. Khundkar, J. T. Bartlett, M. Biswas, J. Chem. Phys. 1995, 102,
6456.
[27] R. C. Ellington, R. L. Henry, J. Am. Chem. Soc. 1949, 71, 2798.
[28] D. A. de Bie, A. Ostrowicz, G. Geurtsen, H. C. van der Plas, Tetrahe-
dron 1988, 44, 2977.
[12] T. Yamamoto, J. Polym. Sci. Part A: Polym. Chem. 1996, 34, 997.
[13] a) S. W. Jessen, J. W. Blatchford, L.-B. Lin, T. L. Gustafson, J.
Partee, J. Shinar, D.-K. Fu, M. J. Marsella, T. M. Swager, A. G. Mac-
Diarmid, A. J. Epstein, Synth. Met. 1997, 84, 501; b) M. Onoda, A.
G. MacDiarmid, Synth. Met. 1997, 91, 307; c) S.-C. Ng, H.-F. Lu, H.
S. O. Chan, A. Fujii, T. Laga, K. Yoshino, Adv. Mater. 2000, 12,
1122.
[14] R. Fink, C. Frenz, M. Thelakkat, H.-W. Schmidt, Macromolecules
1997, 30, 8177.
[15] X. Zhang, A. S. Shetty, S. A. Jenekhe, Acta Polym. 1998, 49, 52.
[16] Z. Peng, M. E. Galvin, Chem. Mater. 1998, 10, 1785.
[17] C. Y. Zhang, J. M. Tour, J. Am. Chem. Soc. 1999, 121, 8783.
[18] a) M. W. C. Dezotti, M.-A. De Paoli, Synth. Met. 1989, 29, E41;
b) D. A. P. Delnoye, R. P. Sijbesma, J. A. J. M. Vekemans, E. W.
Meijer, J. Am. Chem. Soc. 1996, 118, 8717.
[19] R. Wortmann, C. Glania, P. Kr‰mer, R. Matschiner, J. J. Wolff, S.
Kraft, B. Treptow, E. Barbu, D. L‰ngle, G. Gˆrlitz, Chem. Eur. J.
1997, 3, 1765.
Received: April 25, 2003
Revised: July 23, 2003 [F5073]
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2003, 9, 5597 5604
5604