Preparation and nonlinear optics of monodisperse oligo(1,4-phenyleneethynylene)s

Article abstract of DOI:10.1002/1099-0690(200112)2001:23<4431::aid-ejoc4431>3.0.co;2-j

Oligo(1,4-phenyleneethynylene)s 1a-e, with solubilizing propoxy side chains, were prepared by use of Hagihara-Sonogashira coupling reactions. The synthetic strategy was based on a building block system and on the use of trimethylsilyl and triisopropylsily

Full text of DOI:10.1002/1099-0690(200112)2001:23<4431::aid-ejoc4431>3.0.co;2-j

FULL PAPER
Preparation and Nonlinear Optics of Monodisperse
Oligo(1,4-phenyleneethynylene)s
Herbert Meier,*[a] Dirk Ickenroth,[a] Ulf Stalmach,[a] Kaloian Koynov,[b] Ayi Bahtiar,[b] and
Christoph Bubeck[b]
Keywords: Alkynes / Conjugation / Nonlinear optics / Oligomers / Third harmonic generation
Oligo(1,4-phenyleneethynylene)s 1a−e, with solubilizing
propoxy side chains, were prepared by use of
Hagihara−Sonogashira coupling reactions. The synthetic
a bathochromic shift of the long wavelength absorption and
a superlinear increase of the second hyperpolarizability |γ|.
The corresponding third harmonic generation (THG) meas-
strategy was based on a building block system and on the urements were performed using polystyrene matrices and
use of trimethylsilyl and triisopropylsilyl protecting groups variable laser wavelengths. We conclude that the conjuga-
that could be cleaved selectively. The extension of the con-
jugation with an increasing number of repeat units provokes
tion length is much larger than 5 repeat units.
Introduction
Because of their interesting optical, electrical, and opto-
electronic properties, conjugated oligomers are target com-
pounds for many applications in materials science; more-
over, they are model compounds for conjugated
polymers.[1Ϫ9] In this context we decided to study a series
of monodisperse oligo(1,4-phenyleneethynylene)s (OPEs) 1
bearing propoxy side chains. Unsubstituted higher OPEs (n
Ն 3) are difficult to produce because of their extremely low
solubilities. Alkoxy side chains enhance the solubility and
reduce the HOMOϪLUMO gap and the band gap in the
solid state. The pattern of 2,5-disubstitution and the length
of the alkoxy chains have been optimized in the 1,4-pheny-
leneethenylene series 2.[10]
Interest in OPEs and the corresponding polymers (PPEs)
has increased greatly during the previous decade;[11Ϫ36] sys-
tematic studies of structureϪproperty relationships are thus
highly desirable. Here we present the preparation of com-
pounds 1aϪe (n ϭ 1Ϫ5) and compare the third-order non-
linear optical properties in this series with those in the cor-
Scheme 1. Oligo(2,5-dipropoxy-1,4-phenyleneethynylene)s 1 and
oligo(2,5-dipropoxy-1,4-phenyleneethenylene)s 2
Results and Discussion
responding
oligo(2,5-dipropoxy-1,4-phenylenevinylene)
(OPV) series 2 (Scheme 1).[37,38] We have used the method
of third harmonic generation (THG) with variable laser
wavelengths.[37] As the optical properties of conjugated
polymers are determined largely by the extent of their elec-
tron delocalization, investigation of the corresponding oli-
gomers plays an important role in proper understanding of
the scaling of linear and nonlinear optical properties with
the size of the system.
Synthesis
The synthetic strategy for the preparation of the monodi-
sperse oligo(1,4-phenyleneethynylene)s 1aϪe (n ϭ 1Ϫ5) is
based on a building block system. The initial building
blocks are represented by the mono- and dihalogenated 1,4-
dipropoxybenzenes 4Ϫ8, which were obtained through sub-
stitution reactions. Bromination of 1,4-dipropoxybenzene
(3) with equimolar amounts of bromine gave a 76% yield
of 1-bromo-2,5-dipropoxybenzene (4). 1,4-Dibromo-2,5-di-
propoxybenzene (5) was obtained in 86% yield by treatment
of 3 with 2 equiv. of bromine in acetic acid. Direct iodina-
tion of 3 was carried out with iodine and potassium iodate
in the presence of sulfuric acid. Monoiodo compound 6 was
purified by careful distillation (yield 44%), whereas the solid
[a]
Institut für Organische Chemie, Universität Mainz,
Duesbergweg 10Ϫ14, 55099 Mainz, Germany
Fax: (internat.) ϩ 49-(0)6131/392-5396
E-mail: hmeier@mail.uni-mainz.de
[b]
Max-Planck-Institut für Polymerforschung,
Ackermannweg 10, 55128 Mainz, Germany
Eur. J. Org. Chem. 2001, 4431Ϫ4443
WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
1434Ϫ193X/01/1223Ϫ4431 $ 17.50ϩ.50/0
4431

H. Meier, D. Ickenroth, U. Stalmach, K. Koynov, A. Bahtiar, C. Bubeck
FULL PAPER
diiodo compound 7 could be purified by recrystallization
(yield 82%). The mixed bromo-iodo derivative 8 was pre-
pared in 77% yield by treatment of 4 with I2/KIO3/H2SO4.
The opposite sequence for introduction of the halogen sub-
stituents was not successful. Bromination of 6 resulted ex-
clusively in the dibromo compound 5; clearly the iodine
substituent had been replaced in an electrophilic ipso substi-
tution.[39]
In
order
to
introduce
ethynyl
groups,
HagiharaϪSonogashira reactions were applied.[40] Trime-
thylsilyl- and triisopropylsilylethyne reacted with 4Ϫ8
(Scheme 2) in CϪC coupling processes catalyzed by palla-
dium(0)/copper(I) iodide in piperidine. In this manner, the
mono-
and
bis(trialkylsilyl)ethynylbenzenes
9Ϫ15
(Scheme 3) were generated in high yields.
Scheme 2. Halogenation products 4؊8 of 1,4-dipropoxybenzene (3)
The deprotection of the alkynes 9, 10, 12, and 13 was
achieved with sodium hydroxide in methanol or with tetra-
butylammonium fluoride in THF/water (Scheme 4). Since
the bonding of the triisopropylsilyl group is stronger, select-
ive deprotection of 15 was successful by cleavage of the tri-
methylsilyl group with potassium carbonate in methanol/
THF.
Scheme 3. Formation of the alkynes 9؊15 by replacement of the
halogen substituents in 4؊8 by trialkylsilylethynyl groups: i)
Me3SiCϵCH, Pd0, CuI, piperidine; ii) iPr3SiCϵCH, Pd0, CuI,
piperidine
In some cases, in which the yield of the coupling was low,
The preparation of the target compounds 1aϪe was per- we observed increased formation of 1,3-diynes, although
formed by means of the HagiharaϪSonogashira reac- oxygen was carefully excluded.[42] The tolane derivative 1a,
tion,[40] in which a CϪC coupling of iodo- or bromoarenes the first compound in the oligomer series 1, was formed on
and ethynylarenes takes place. Catalytic amounts of bi- treatment of the iodobenzene 6 with the phenylacetylene 16,
s(triphenylphosphane)palladium dichloride, copper(I) iod- whilst the diiodo compound 7 and 16 accordingly yielded
ide, and triphenylphosphane were used for the process, the next higher oligomer 1b.
which was normally run in piperidine. Toluene was added
The original plan for the synthesis of compound 1c was
based on the CϪC coupling of the bromotolane system 20
in some cases to improve the solubility (Scheme 5).
The true catalytic species is the (triphenylphosphane)Pd0 with the ethynyltolane 22. The component 20 was obtain-
complex, which inserts into the carbonϪhalogen bond. Un- able from 16 and 1-bromo-4-iodobenzene (8) in an almost
der the conditions applied here, the reactions would in prin- quantitative
yield;
the
reactivity
in
the
ciple also work in the absence of copper(I) iodide;[41] how- HagiharaϪSonogashira process was much higher on the
ever, we found that the best yields were obtained with iodo side than on the bromo side. CϪC coupling of 20 with
iodoarenes and freshly precipitated CuI. Piperidine served triisopropylsilylethyne to give 21 and deprotection of 21 to
as scavenger for the eliminated hydrogen bromide or iodide. give 22 gave yields of 99 and 87%, respectively. The syn-
4432
Eur. J. Org. Chem. 2001, 4431Ϫ4443

Preparation and Nonlinear Optics of Monodisperse Oligo(1,4-phenyleneethynylene)s
FULL PAPER
tions can have a dramatic effect on optical properties. A
striking example is represented by the pushϪpull-substi-
tuted OPEs obtained by HPLC separation of polydisperse
products.[17]
Optical Studies
UV/Vis absorption spectra of diluted solutions of OPEs
(1aϪe) in CHCl3 are shown in Figure 1. The wavelengths
of the absorption maxima λmax show the expected strong
bathochromic shift with increasing number n of repeat un-
its, typical for short oligomers of conjugated systems. The
corresponding molar extinction coefficients εmax also in-
crease with n (see Table 1). Our studies of nonlinear optical
properties required thin films of OPEs on fused silica sub-
strates. Films of pure OPEs lose their optical quality be-
cause OPEs tend to crystallize and exhibit strong light scat-
tering. We therefore prepared thin films of OPEs dispersed
in polystyrene (PS) as described in the Exp. Sect. The λmax
and absorption coefficient αmax data of the thin films are
given in Table 1. They show spectroscopic data similar to
those obtained for the CHCl3 solutions.
Quantitative data concerning the chain length L, defined
as the distance between the terminal carbon atoms of the
benzene rings, were obtained by X-ray structure investi-
gation of 1a and 1b. The lengths L of 1cϪe were extrapol-
ated by using the identical lengths of the repeat unit
(0.681 nm) and of the phenyl end groups (0.271 nm) found
for 1a and 1b.[43]
Scheme 4. Generation of the phenylethynes 16؊19 by deprotection
of 9, 10, 12, 13, and 14
By using the method described in the Exp. Sect. for the
THG (third harmonic generation) measurement, we evalu-
ated modulus |χ(3)| and phase angle ϕ of the macroscopic,
complex third-order susceptibility χ(3)(Ϫ3ω;ω,ω,ω) ϭ |χ(3)
|
thetic strategy thus seemed very promising, but the final exp (iϕ) of the films. Two points should be emphasized:
CϪC coupling 22 ϩ 20 Ǟ 1c gave only poor yields. We (i) the third-order susceptibility we have measured is the
therefore had to develop a new approach for 1c, coupling result of the contributions of the OPE oligomer and the
22 with the iodo compound 11 instead of with the bromo PS matrix,
compound 20 to obtain 23 in a yield of 58%. Deprotection
(ii) the |χ(3)| values show strong spectral dependence on
of 23 with tetrabutylammonium fluoride furnished alkyne the laser frequency ω used, because of resonances with elec-
24, which was coupled with the iodobenzene derivative 6. tronic states of the compounds; these occur if 3ω or 2ω
Though the yield of the latter CϪC coupling is moderate, match an electronic transition.[44,45]
the total yield of 1c from 22 could be doubled by use of the
alternate route.
With this in mind, we conducted our THG experiments
at the three-photon resonance condition with laser wave-
The preparation of compound 1d was also achieved by lengths λL ϭ 3λmax. This ensures sufficient detection sensit-
two different pathways. The diyne 17 was subjected to a ivity and comparable measurement conditions for the thin
(3)
twofold HagiharaϪSonogashira reaction (17 ϩ 2·20 Ǟ 1d) OPE films (1aϪe). The results for modulus |χ | and phase
res
or to a twofold coupling with 8, which reacted selectively angle ϕ are given in Table 1. Clearly the modulus of the
on the iodo side (17 ϩ 2·8 Ǟ 25); oligomer 1d could sub- third-order susceptibility increases with chain length L. The
sequently be obtained in situ by coupling of 25 with the phase angle ϕ also increases on going from 1a to 1c and
alkyne 16 at both ends. The yield of the first variant was then stays constant Ϫ at around 90°.
much better: 76% in comparison to 15%.
We interpret these changes of ϕ in terms of different con-
However, the dibromo compound 25 could be used for tributions of PS matrix and OPEs to the total sum of the
two consecutive couplings: namely 25 ϩ 19 Ǟ 26 and 26 ϩ complex χ(3) value, which is the vector sum of χ and χ
(3)
PS
(3)
16 Ǟ 27. Deprotection of 27 gave 28, and final coupling of OPE. Because our THG measurements were always per-
(3)
28 with 6 the target oligomer 1e.
formed at λL ϭ 3λmax of the OPEs, the contribution χ
OPE
The oligomers 1aϪe are distinct from other known OPEs is imaginary and ϕOPE ϭ 90°, which is typically observed
or PPEs insofar as they have identical substitution patterns at the peak of the three-photon resonance.[37,45] On the
(3)
in each benzene ring in the chain and do not have divergent other hand, χ is nonresonant and real because λL is much
PS
end groups that interact with the π system. Such interac- larger than 3λmax of PS, which implies ϕPS ϭ 0°. As the
Eur. J. Org. Chem. 2001, 4431Ϫ4443
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H. Meier, D. Ickenroth, U. Stalmach, K. Koynov, A. Bahtiar, C. Bubeck
FULL PAPER
Scheme 5. Preparation of the target compounds, the monodisperse oligo(2,5-dipropoxy-1,4-phenyleneethynylene)s 1a؊e: i) Pd0, CuI,
piperidine
(3)
modulus |χ
| increases strongly with chain length, the
OPE
(3)
contribution of PS to the total sum of |χ | becomes negli-
res
gible for the longer oligomers 1cϪe and the total phase
angle ϕ approaches 90°.
In order to understand the influence of chain length on
nonlinear optical properties, it is better to consider the se-
cond hyperpolarizability γ, which is a molecular parameter,
instead of the macroscopic susceptibility χ(3). In the cgs sys-
tem of units, these quantities are related by Equation (1)
where N is the number of oligomers per unit volume.[44,45]
χ(3)(Ϫ3ω;ω,ω,ω) ϭ N f(3ω) [f(ω)]3 γ(Ϫ3ω;ω,ω,ω)
(1)
We have calculated N as in Equation (2) where NA is the
Avogadro constant, MOPE and cOPE are the molecular mass
Figure 1. UV/Vis spectra of OPEs 1a؊e in CHCl3
4434
Eur. J. Org. Chem. 2001, 4431Ϫ4443

Preparation and Nonlinear Optics of Monodisperse Oligo(1,4-phenyleneethynylene)s
FULL PAPER
ence of the polystyrene matrix is negligible in both series
for n Ն 3.
The superlinear increase of γ with L has attracted wide
interest. Early theoretical investigations for very short con-
jugated oligomers (L Ͻ 2 nm) yielded a power law accord-
ing to Equation (4) with an exponent µ in the order of 4 to
5, as summarized in a recent review.[45]
Table 1. Linear and nonlinear optical properties of the oligomers
1aϪe in highly diluted solutions (CHCl3) and in thin films of poly-
styrene (PS) with (10.00 Ϯ 0.03)% (mass) of OPE
Compound
1a
1b
1c
1d
1e
Repeat units n
1
2
3
4
5
Chain length L [nm]
Absorption in CHCl3
λmax [nm] (Ϯ 1 nm)
0.952 1.633 2.314 2.995 3.676
γ ~ Lµ ~ nµ
(4)
338
378
399
412
419
εmax [L·molϪ1·cmϪ1] (Ϯ 3%) 15900 39000 54700 80600 112100
More refined calculations for longer chains revealed that
µ is itself a function of chain length L or number of repeat
units n.[51Ϫ56] The function µ ϭ µ(n) describes the transition
from the short chain limit (µ ϭ 4Ϫ5) to the limiting case
of very long chains. In the latter case the π electrons of the
entire chain are no longer correlated to each other. Indi-
vidual chain segments respond independently to the ex-
ternal electric fields of the light wave. This situation is com-
monly called saturation of the polarizabilities and the crit-
ical length at which this occurs is termed the conjugation
length.[45,57]
Absorption in PS films
λmax [nm] (Ϯ 3 nm)
335
377
394
410
417
αmax [104 cmϪ1] (Ϯ 3%)
0.923 1.220 1.481 1.781 2.115
THG of films
res
(3)
|χ | [10Ϫ13 esu]
2.05
Ϯ 0.4 Ϯ 0.3 Ϯ 0.6 Ϯ 0.8 Ϯ 1.2
33 66 86 84 94
4.82 7.96 12.1 13.4
ϕ [°] (Ϯ 10°)
|γres| [10Ϫ32 esu]
0.134 0.81 2.04 3.93 5.47
Ϯ 0.03 Ϯ 0.1 Ϯ 0.3 Ϯ 0.5 Ϯ 0.8
and the concentration by weight of the respective OPE
The data for the OPEs reveal exponents µ1,2 ϭ 3.3 and
µ4,5 ϭ 1.6, which refer to the changes of |γres| from n ϭ 1
to n ϭ 2 and from n ϭ 4 to n ϭ 5, respectively. Obviously,
the OPEs 1aϪe are excellent model systems with which to
study conjugation effects in one-dimensional π-electron sys-
tems and, especially, to investigate the transition regime be-
tween the limiting cases of short chains and saturation.
compound, and ρ is the density of the film.
N ϭ NAρcOPE/MOPE
(2)
The dimensionless Lorentz local field factors f(ω) depend
on the refractive index n(ω) and are given by[44] Equation
(3).
f(ω) ϭ [n2(ω) ϩ 2]/3
(3)
For the determination of |γres|, we used the imaginary
(3)
part of the total third-order susceptibility |χ | of the film.
res
Summary and Conclusions
The molecular hyperpolarizabilities |γres| of the different
OPEs 1aϪe are listed in the last row of Table 1 and their
dependence on chain length L is plotted in Figure 2.
Oligo(1,4-phenyleneethynylene)s 1aϪe have been pre-
pared by a building block approach, by application of the
HagiharaϪSonogashira reaction and selective deprotection
of different trialkylsilyl protecting groups (Schemes 1Ϫ5).
Extension of the conjugation in the series of the oligo-
mers 1aϪe causes a significant bathochromic shift of the
long wavelength absorption; the λmax values of the corres-
ponding bands are shifted in chloroform from 338 nm for
1a to 419 nm for 1e and, dispersed in polystyrene, from
335 nm for 1a to 417 for 1e. These data differ significantly
from other OPE series, which show convergence even at
λϱ ϭ 387 nm[17] or at about 440 nm.[20][58] As mentioned
before, however, these series contain end groups such as
nitro, dimethylamino, bromo, or trialkylsilyl, which interact
with the π electrons of the conjugated chain. The absorp-
tion intensity increases with growing numbers n of repeat
units; the average εmax/n values of the solution spectra are
Figure 2. Double logarithmic plot of molecular hyperpolarizability
|γres| of OPEs 1a؊e versus chain length L; the dashed line repres-
ents an increase from 1a to 1b according to a power law |γres| ~ L3·3
The data show a superlinear increase of |γres| with L, (19.2 Ϯ 3.3)·103 l·molϪ1 cmϪ1 for the series 1aϪe.
which has similarly been observed in the cases of other con- The THG measurements for the oligomers in polystyrene
jugated oligomers such as oligophenylenes,[46] oligothioph- show an increase in the second hyperpolarizability |γres
enes,[47,48] and oligo-p-phenylenevinylenes.[37,49] A compar- from 0.13·10Ϫ32 esu for 1a to 5.5·10Ϫ32 for 1e. The |γres
|
|
ison of the alkyne series 1 with the corresponding all-trans- values for the alkyne series 1 are significantly higher (by a
alkene series 2 demonstrates that the |γres| values in the factor of 5Ϫ7) than those for the all-trans-alkene series 2.[50]
series 1 are higher: 1d, for example, has a |γres| value of For a certain number n of repeat units, the length L of the
3.93·10Ϫ32 esu, whereas the corresponding conjugated olig- oligomers is similar in both series; the conjugation effect
ophenylenevinylene 2 with n ϭ 4 and 2,5-dipropoxy-substi- [E(n ϭ 1) Ϫ E(n Ǟ ϱ)][22] is somewhat greater in the alkene
tuted benzene rings has a |γres| of 7.34·10
.
Ϫ33 [49,50] The influ- series. Interpretation of this result thus warrants further
Eur. J. Org. Chem. 2001, 4431Ϫ4443
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H. Meier, D. Ickenroth, U. Stalmach, K. Koynov, A. Bahtiar, C. Bubeck
FULL PAPER
the solution over 3 h. After stirring for 12 h at room temperature,
the mixture was poured into ice/water (500 mL). The water phase
was extracted with chloroform (5 ϫ 100 mL) and the organic
phases were neutralized with saturated NaHCO3 and dried with
Na2SO4. The solvent was evaporated and the residue was recrystal-
lized from methanol. Yield: 75.4 g (86%) of colorless crystals, m.p.
study. A double logarithmic plot (Figure 2) of |γres| versus
the lengths L of the conjugated chains reveals a superlinear
increase of |γres| but its slope decreases with increasing L.
However, saturation for large values of L is not yet discern-
ible, which shows that the conjugation length of OPEs is
much greater than 5 repeat units.
1
73 °C; H NMR (CDCl3): δ ϭ 1.04 (t, 6 H, CH3), 1.79 (m, 4 H,
CH2), 3.90 (t, 4 H, OCH2), 7.07 (s, 2 H, 3-H); 13C NMR (CDCl3):
δ ϭ 10.5 (2 C, CH3), 22.6 (2 C, CH2), 71.8 (2 C, OCH2), 111.1 (2
Cq, C-1), 118.5 (2 C, C-3), 150.1 (2 Cq, C-2); EI MS (70 eV): m/z
(%) ϭ 354.3 (9) [Mϩ], 352.2 (20) [Mϩ], 350.1 (10) [Mϩ], 270.0 (45)
[Mϩ Ϫ 2 C3H7], 268.0 (95) [Mϩ Ϫ 2 C3H7], 266.0 (47) [Mϩ Ϫ 2
C3H7], 43.4 (100) [C3H7ϩ]; IR (KCl): ν˜ ϭ 2970, 2930, 1495, 1455,
1360, 1270, 1215, 1070, 1020, 855, 815, 775 cmϪ1; C12H16Br2O2
(352.1): calcd. C 40.94, H 4.58, Br 45.39; found C 41.04, H 4.63,
Br 45.18.
Experimental Section
General: Melting points were determined with a Büchi melting
point apparatus and are uncorrected; IR spectra were obtained
with a Beckman Acculab 4 or a PerkinϪElmer GX FT-IR spectro-
meter; 1H and 13C NMR spectra were recorded with a Bruker ARX
400 spectrometer in CDCl3 (TMS as internal standard) and mass
spectra with a Finnigan MAT 95 spectrometer; UV/Vis/NIR trans-
mission spectra of solutions in CHCl3 and reflection spectra of thin
films (polystyrene matrix) were recorded with PerkinϪElmer
Models 9 and 900 spectrophotometers at ambient temperature.
1-Iodo-2,5-dipropoxybenzene (6): Compound 3 (30.0 g, 0.15 mol)
was dissolved in acetic acid (300 mL) and tetrachloromethane (20
mL). To this solution were added iodine (19.5 g, 0.08 mol), conc.
sulfuric acid (6 mL), distilled water (25 mL), and finally potassium
iodate (5.6 g, 0.026 mol). The mixture was stirred for 5 h at 80 °C
and for 10 h at room temperature. To remove excess iodine,
NaHSO3 was added until the violet color of iodine disappeared.
The mixture was poured into ice/water (1.5 L) and extracted with
chloroform (5 ϫ 300 mL). The organic phases were neutralized
with saturated NaHCO3 and dried with Na2SO4. The solvent was
evaporated and the residue was distilled under vacuum. Yield:
19.9 g (40%) of a colorless oil; 1H NMR (CDCl3): δ ϭ 1.00/1.06 (2
t, 2 ϫ3 H, CH3), 1.73 (m, 4 H, CH2), 3.82/3.89 (2 t, 2 ϫ2 H,
OCH2), 6.70 (d, 1 H, 3-H), 6.82 (dd, 1 H, 4-H), 7.31 (d, 1 H, 6-
H); 13C NMR (CDCl3): δ ϭ 10.5/10.7 (2 C, CH3), 22.6/22.7 (2 C,
CH2), 70.4/71.6 (2 C, OCH2), 87.0 (1 Cq, C-1), 113.1/115.4 (2 C,
C-3, C-4), 125.3 (1 C, C-6), 152.1/153.7 (2 Cq, C-2, C-5); FD MS:
m/z (%) ϭ 320 (100) [Mϩ]; IR (NaCl): ν˜ ϭ 2964, 2936, 2877, 1599,
1570, 1490, 1467, 1389, 1271, 1210, 1067, 1022, 981, 865, 801, 735
cmϪ1; C12H17O2I (320.2): calcd. C 45.02, H 5.35, I 39.64; found C
Preparations
1,4-Dipropoxybenzene (3): Hydroquinone (175.0 g, 1.59 mol) was
dissolved in degassed ethanol (1.5 L). After addition of KOH
(220.0 g, 3.92 mol), the solution was stirred under reflux for 20
min. 1-Bromopropane was added dropwise to the light brown solu-
tion over 40 min, followed by stirring under reflux for 2 h. Ethanol
was then removed by distillation. The residue was dissolved in chlo-
roform and extracted with water (3 ϫ 200 mL). The combined
organic phases were washed with saturated NaHCO3, dried with
Na2SO4, and concentrated. The remaining solid was recrystallized
from methanol. Yield 263.6 g (85%) of colorless crystals; m.p. 49
°C. (ref.[59]: m.p. 48 °C); 1H NMR (CDCl3): δ ϭ 1.08 (t, 6 H, CH3),
1.80 (m, 4 H, CH2), 3.89 (t, 4 H, OCH2), 6.68 (s, 4 H, 2-H); 13C
NMR (CDCl3): δ ϭ 10.5 (2 C, CH3), 22.7 (2 C, CH2), 70.1 (2 C,
OCH2), 115.4 (4 C, C-2), 153.2 (2 Cq, C-1); EI MS (70 eV): m/z
(%) ϭ 194 (17) [Mϩ], 152 (9) [Mϩ Ϫ C3H6], 110 (100) [Mϩ
2C3H6], 81 (6), 43 (18); C12H18O2 (194.3): calcd. C 74.18, H 9.34;
found C 74.12, H 9.33.
Ϫ
45.14, H 5.39, I 39.67.
1,4-Diiodo-2,5-dipropoxybenzene (7): Compound 3 (40.0 g, 0.21
mol) was dissolved in acetic acid (120 mL) and tetrachloromethane
(30 mL). To this solution were added iodine (45.7 g, 0.18 mol),
conc. sulfuric acid (14 mL), distilled water (7 mL), and finally pot-
assium iodate (18.4 g, 0.086 mol). The mixture was stirred for 24 h
under reflux. To remove excess iodine, NaHSO3 was added until
the violet color of iodine disappeared. The mixture was poured into
ice/water (1.5 L) and extracted with chloroform (5 ϫ 300 mL). The
organic phases were neutralized with saturated NaHCO3 and dried
with Na2SO4. After evaporation of the solvent, the residue was
recrystallized from methanol. Yield: 75.0 g (82%) of colorless crys-
1-Bromo-2,5-dipropoxybenzene (4): Compound 3 (65.5 g, 0.34 mol)
and sodium acetate (26.7 g, 0.33 mol) were dissolved in acetic acid
(200 mL). At 0 °C, bromine (53.9 g, 0.337 mol) was slowly added
to the solution over 5 h. After stirring for 12 h at room temperature,
the mixture was poured into water (1.5 L). After extraction with
chloroform (5 ϫ 150 mL), the organic phases were neutralized with
saturated NaHCO3 and dried with Na2SO4. The solvent was evap-
orated and the remaining brown oil was distilled under vacuum.
1
Yield 69.7 g (76%) of a colorless oil; H NMR (CDCl3): δ ϭ 0.96/
1
1.08 (2 t, 2 ϫ3 H, CH3), 1.78 (m, 4 H, CH2), 3.83/3.90 (2 t, 2 ϫ2
H,OCH2), 6.77 (m, 2 H, 3-H, 4-H), 7.09 (d, 1 H, 6-H); 13C NMR
(CDCl3): δ ϭ 11.1/11.2 (2 C, CH3), 23.1/23.1 (2 C, CH2), 71.2/72.1
(2 C, OCH2), 108.8 (1 Cq, C-1), 115.7/121.5/123.4 (3 C, C-3, C-4,
C-6), 150.9/151.6 (2 Cq, C-2,C-5); EI MS (70 eV): m/z (%) ϭ 274.1
(22) [Mϩ], 272.1 (23) [Mϩ], 232.0 (15) [Mϩ Ϫ C3H7], 230.0 (15)
[Mϩ Ϫ C3H7], 190.1 (100) [Mϩ Ϫ 2 C3H7], 188.1 (95) [Mϩ Ϫ 2
C3H7], 43.5 (60) [C3H7ϩ]; IR (KCl): ν˜ ϭ 2980, 2930, 1590, 1565,
1485, 1455, 1380, 1260, 1205, 1060, 975, 795 cmϪ1; C12H17BrO2
(273.0): calcd. C 52.76, H 6.27, Br 29.25; found C 53.01, H 6.31,
Br 29.14.
tals, m.p. 85 °C; H NMR (CDCl3): δ ϭ 1.05 (t, 6 H, CH3), 1.57
(m, 4 H, CH2), 3.88 (t, 4 H, OCH2), 7.15 (s, 2 H, 3-H); 13C NMR
(CDCl3): δ ϭ 10.7 (2 C, CH3), 22.6 (2 C, CH2), 71.8 (2 C, OCH2),
86.3 (2 Cq, C-1), 122.7 (2 C, C-3), 152.8 (2 Cq, C-2); FD MS: m/z
ϩ
ϩ
˜
(%) ϭ 447.7 (14) [M ], 446.7 (100) [M ]; IR (KCl): ν ϭ 2961, 2910,
2878, 1489, 1451, 1350, 1265, 1210, 1057, 1009, 852, 799, 770 cmϪ1
;
C12H16O2I2 (446.1): calcd. C 32.31, H 3.62, I 56.90; found C 32.34,
H 3.51, I 57.29.
1-Bromo-4-iodo-2,5-dipropoxybenzene (8): Compound 4 (45.0 g,
0.17 mol) was dissolved in acetic acid (110 mL) and tetrachlorome-
thane (27 mL). To this solution were added iodine (41.4 g, 0.16
mol), conc. sulfuric acid (14 mL), distilled water (7 mL), and finally
1,4-Dibromo-2,5-dipropoxybenzene (5): Compound 3 (48.6 g, 0.25
mol) and sodium acetate (40.0 g, 0.49 mol) were dissolved in acetic potassium iodate (14.5 g, 0.07 mol). The mixture was stirred for
acid (300 mL). Bromine (80.0 g, 0.50 mol) was added dropwise to 5 h under reflux. To remove excess iodine, NaHSO3 was added until
4436
Eur. J. Org. Chem. 2001, 4431Ϫ4443

Preparation and Nonlinear Optics of Monodisperse Oligo(1,4-phenyleneethynylene)s
FULL PAPER
the violet color of iodine disappeared. The mixture was poured into
thylsilylacetylene (1.0 g, 9.9 mmol) were added. The mixture was
ice/water (1.0 L) and extracted with chloroform (5 ϫ 100 mL). The stirred for 18 h and purified as described above. Yield: 1.7 g (98%)
1
organic phases were neutralized with saturated NaHCO3 and dried
with Na2SO4. The solvent was evaporated and the residue was 18 H, SiϪCH3), 1.04 (t, 6 H, CH3), 1.79 (m, 4 H, CH2), 3.89 (t, 4
recrystallized from methanol. Yield: 50.8 g (77%) of colorless crys-
H, OCH2), 6.88 (s, 2 H, 3-H); 13C NMR (CDCl3): δ ϭ 0.1 (6 C,
of colorless crystals, m.p. 101 °C; H NMR (CDCl3): δ ϭ 0.23 (s,
1
tals, m.p. 73 °C; H NMR (CDCl3): δ ϭ 1.04/1.05 (2 t, 2 ϫ 3 H, SiϪCH3), 10.5 (2 C, CH3), 22.7 (2 C, CH2), 71.0 (2 C, OCH2),
CH3), 1.77 (m, 4 H, CH2), 3.88/3.89 (2 t, 2 ϫ2 H, OCH2), 6.96 (s, 100.1 (2 C, ϵC-Si), 101.0 (2 C, ArϪCϵ), 114.0 (2 Cq, C-1), 117.3
1 H, 6-H), 7.26 (s, 1 H, 3-H); 13C NMR (CDCl3): δ ϭ 10.5/10.7 (2 (2 C, C-3), 154.0 (2 Cq, C-2); FD MS: m/z (%) ϭ 386.4 (100) [Mϩ],
ϩ
˜
C, CH3), 22.5 (2 C, CH2), 71.8/71.8 (2 C, OCH2), 84.8 (1 Cq, C-4), 387.4 (23) [M ]; IR (KBr): ν ϭ 2963, 2913, 2875, 2156, 1504, 1390,
112.5 (1 Cq, C-1), 117.1 (1 C, C-6), 124.3 (1 C, C-3), 150.4 (1 Cq, 1275, 1246, 1225, 1041, 1023, 899, 838, 759 cmϪ1; C22H34O2Si2
C-2), 152.5 (1 Cq, C-5); FD MS: m/z (%) ϭ 399.9 (100) [Mϩ], 397.9 (386.7): calcd. C 68.34, H 8.86; found C 68.44, H 8.91.
ϩ
˜
(91) [M ]; IR (KBr): ν ϭ 2964, 2933, 2911, 2879, 1493, 1456, 1380,
1-Iodo-2,5-dipropoxy-4-triisopropylsilylethynylbenzene (11): Com-
pound 7 (50.0 g, 0.112 mol) and triisopropylsilylacetylene (13.6 g,
0.075 mol) were dissolved in dry piperidine (150 mL) and the sys-
tem was flushed with nitrogen. Bis(tetraphenylphosphane)pallad-
ium dichloride (2.0 g, 2.85 mmol), copper(I) iodide (0.6 g,
3.15 mmol), and triphenylphosphane (0.8 g, 3.15 mmol) were ad-
ded. After 12 h stirring at room temperature, the solvent was evap-
orated and chloroform was added to the residue. After extraction
with saturated NH4Cl, water, and saturated NaHCO3, the organic
phase was dried with Na2SO4 and the chloroform was then re-
moved by distillation. The slightly brown crystals were recrystal-
lized from n-hexane (200 mL). The product was dissolved in diethyl
ether (60 mL) and mixed with ethanol (150 mL). Fractional crystal-
lization produced a main fraction that was purified by chromato-
graphy on silica gel (n-hexane/CH2Cl2, 5:1). Yield: 25.4 g (68%) of
1268, 1211, 911, 852, 804, 774 cmϪ1; C12H16BrIO2 (399.1): calcd.
C 36.12, H 4.04, Br 20.02, I 31.80; found C 36.30, H 4.13, Br 20.51,
I 31.99.
2,5-Dipropoxy-1-trimethylsilylethynylbenzene (9).
؊ Preparation
from 4: Compound 4 (19.0 g, 0.059 mol) was dissolved in dry piper-
idine (150 mL) and the system was flushed with nitrogen. Bis(tetra-
phenylphosphane)palladium dichloride (1.2 g, 1.68 mmol), cop-
per(I) iodide (0.65 g, 3.35 mmol), and triphenylphosphane (0.88 g,
3.35 mmol) were added to the mixture. Trimethylsilylacetylene
(8.2 g, 0.083 mol) was added to the clear solution. After 6 d, the
solvent was evaporated, chloroform was added to the residue, and
the solution was extracted with saturated NH4Cl and water. After
having been washed with saturated NaHCO3, the organic phases
were dried with Na2SO4. Filtration through a short silica gel col-
umn produced a black oil, which was purified by vacuum distilla-
tion. Yield: 14.3 g (83%) of a colorless oil. Ϫ Preparation from 6:
Compound 6 (22.4 g, 0.07 mol) was dissolved in dry piperidine (200
mL) and the system was flushed with nitrogen. Bis(tetraphenylpho-
sphane)palladium dichloride (1.2 g, 1.68 mmol), copper(I) iodide
(0.7 g, 3.5 mmol), and triphenylphosphane (0.9 g, 3.5 mmol) were
added. The reaction time was 1.5 h. Purification was according to
the procedure described above. Yield: 19.1 g (94%) of a colorless
1
colorless crystals, m.p. 63 °C; H NMR (CDCl3): δ ϭ 1.08 (m, 27
H, CH3, SiϪCϪH, SiϪCϪCH3), 1.79 (m, 4 H, CH2), 3.88 (m, 4
H, OCH2), 6.82 (s, 1 H, 3-H), 7.22 (s, 1 H, 6-H); 13C NMR
(CDCl3): δ ϭ 10.6/10.8 (2 C, CH3), 11.4 (3 C, Si-CH), 18.7 (6 C,
SiϪCϪCH3), 22.7 (2 C, CH2), 71.1/71.7 (2 C, OCH2), 87.6 (1 Cq,
C-1), 95.8/102.6 (2 C, ArϪCϵC-Si), 113.8 (1 Cq, C-4), 116.7 (1 C,
C-3), 123.5 (1 C, C-6), 151.6 (1 Cq, C-2), 155.1 (1 C, C-5); FD MS:
m/z (%) ϭ 501.8 (18) [Mϩ], 500.7 (100) [Mϩ]; IR (KBr): ν˜ ϭ 2962,
2942, 2866, 2157, 1500, 1489, 1468, 1372, 1266, 1213, 1065, 1044,
1020, 883, 854, 831, 799, 769, 677 cmϪ1; C23H37IO2Si (500.5):
calcd. C 55.19, H 7.45; found C 55.02, H 7.43.
1
oil; n2D0 ϭ 1.5109; H NMR (CDCl3): δ ϭ 0.24 (s, 9 H, SiϪCH3),
0.99/1.06 (2 t, 2 ϫ 3 H, CH3), 1.75/1.84 (2 m, 2 ϫ 2 H, CH2), 3.83/
3.89 (2 t, 2 ϫ 2 H, OCH2), 6.74 (d, 1 H, 3-H), 6.80 (dd, 1 H, 4-
H), 6.94 (d, 1 H, 6-H); 13C NMR (CDCl3): δ ϭ 0.01 (3 C, SiϪCH3),
10.5/10.6 (2 C, CH3), 22.6/22.8 (2 C, CH2), 70.2/71.2 (2 C, OCH2),
98.2 (1 C, SiϪC), 101.4 (1 C, Ar-C), 113.5 (1 Cq,C-1), 114.2 (1 C,
C-3), 117.0 (1 C, C-4), 118.7 (1 C, C-6), 152.7/154.7 (2 Cq, C-2, C-
5); FD MS: m/z (%) ϭ 289.9 (100) [Mϩ], 291.0 (21) [Mϩ], 292.0 (5)
[Mϩ]; IR (KBr): ν˜ ϭ 2964, 2879, 2156, 1498, 1469, 1389, 1274,
1228, 1171, 1130, 1068, 857, 800 cmϪ1; C17H26O2Si (290.5): calcd.
C 70.29, H 9.02; found C 70.68, H 8.90.
2,5-Dipropoxy-1,4-bis(triisopropylsilylethynyl)benzene (12): Com-
pound 7 (5.0 g, 11.2 mmol), bis(tetraphenylphosphane)palladium
dichloride (0.4 g, 0.57 mmol), copper(I) iodide (0.21 g, 1.1 mmol),
triphenylphosphane (0.3 g, 1.1 mmol), and triisopropylsilylace-
tylene (4.8 g, 0.026 mol) were dissolved in dry piperidine (80 mL)
and the system was flushed with nitrogen. After the mixture had
been stirred for 3 d, the solvent was evaporated and chloroform
was added to the residue. The organic phase was extracted with
saturated NH4Cl, water, and saturated NaHCO3. The crude prod-
uct was added to boiling methanol and filtered. The filter residue
was recrystallized from 650 mL of ethanol. Yield: 5.5 g (93%) of
2,5-Dipropoxy-1,4-bis(trimethylsilylethynyl)benzene (10).
؊ Pre-
paration from 5: Compound 5 (20.0 g, 0.057 mol) was dissolved in
dry piperidine (150 mL) and the system was flushed with nitrogen.
Bis(tetraphenylphosphane)palladium dichloride (2.0 g, 2.85 mmol),
copper(I) iodide (1.1 g, 5.7 mmol), and triphenylphosphane (1.5 g,
5.7 mmol) were added. Trimethylsilylacetylene (14.0 g, 0.143 mol)
was added to this clear solution. The mixture was stirred for 3 h at
50 °C. The solvent was then evaporated, and chloroform was added
to the residue and extracted with saturated NH4Cl and water. After
having been washed with saturated NaHCO3, the organic phases
were dried with Na2SO4. The crude product was purified by chro-
matography (toluene/n-hexane, 1:1). Yield: 19.0 g (86%) of colorless
crystals, m.p. 101 °C. Ϫ Preparation from 7: Compound 7 (2.0 g,
4.5 mmol) was dissolved in dry piperidine (20 mL) and the system
was flushed with nitrogen. Bis(tetraphenylphosphane)palladium
1
colorless crystals, m.p. 164 °C; H NMR (CDCl3): δ ϭ 1.02 (t, 6
H, CH3), 1.12 (s, 21 H, SiϪCϪH, SiϪCϪCH3), 1.78 (m, 4 H,
CH2), 3.89 (t, 4 H, OCH2), 6.85 (s, 2 H, 3-H); 13C NMR (CDCl3):
δ ϭ 10.6 (2 C, CH3), 11.4 (6 C, SiϪCϪH), 18.7 (12 C, SiϪCϪCH3),
22.7 (2 C, CH2), 71.1 (2 C, OCH2), 96.3/103.2 (4 C, CϵC), 114.3
(2 Cq, C-1), 117.5 (2 C, C-3), 154.2 (2 Cq, C-2); EI MS (70 eV): m/
z (%) ϭ 555.4 (48) [Mϩ], 554.5 (100) [Mϩ], 512.1 (15) [Mϩ
Ϫ
C3H7], 511.2 (33) [Mϩ Ϫ C3H7], 469.9 (8) [Mϩ Ϫ 2C3H7], 468.8
(16) [Mϩ Ϫ 2C3H7], 43.5 (35) [C3H7 ]; IR (KBr): ν ϭ 2944, 2866,
ϩ
˜
2153, 1500, 1473, 1390, 1222, 1202, 1095, 887, 860, 798 cmϪ1
;
C34H58O2Si2 (554.4): calcd. C 73.58, H 10.53; found C 73.48, H
10.47.
dichloride (0.24 g, 0.55 mmol), copper(I) iodide (0.12 g, 1-Bromo-2,5-dipropoxy-4-trimethylsilylethynylbenzene (13): Com-
0.63 mmol), triphenylphosphane (0.24 g, 0.91 mmol), and trime-
pound 8 (20.0 g, 0.05 mol) and a catalyst mixture of bis(tetraphen-
Eur. J. Org. Chem. 2001, 4431Ϫ4443
4437

H. Meier, D. Ickenroth, U. Stalmach, K. Koynov, A. Bahtiar, C. Bubeck
ylphosphane)palladium dichloride (0.9 g, 1.25 mmol), copper(I) After the solution had stirred for 12 h, the solvent was evaporated
FULL PAPER
iodide (0.5 g, 2.5 mmol), and triphenylphosphane (0.7 g, 2.5 mmol)
was dissolved in dry piperidine (200 mL) and the system was
and chloroform was added to the residue. The organic phase was
extracted with saturated NH4Cl, water, and saturated NaHCO3.
flushed with nitrogen. Trimethylsilylacetylene (5.4 g, 0.055 mol) Filtration through a short silica gel column produced a brown solid
was added to the slightly brown solution in small fractions. After that was recrystallized from 170 mL of methanol. Yield: 21.0 g
1
the solution had stirred for 2.5 h, the solvent was evaporated and (84%) of yellow crystals, m.p. 85 °C; H NMR (CDCl3): δ ϭ 0.23
chloroform was added to the oily residue. The organic phase was
extracted with saturated NH4Cl, water, and saturated NaHCO3.
Filtration through a short silica gel column produced a solid, which
(s, 9 H, SiϪCH3), 1.01/1.04 (2 t, 2 ϫ 3 H, CH3), 1.11 (s, 21 H,
SiϪCH, SiϪCHϪCH3), 1.78 (m, 4 H, CH2), 3.87/3.90 (2 t, 2 ϫ 2
H, OCH2), 6.86/6.86 (2 s, 2 ϫ 1 H, 3-H, 6-H); 13C NMR (CDCl3):
was recrystallized from 80 mL of methanol. Yield: 17.8 g (96%), δ ϭ Ϫ0.04 (3 C, SiϪCH3), 10.5/10.6 (2 C, CH3), 11.4 (3 C, Si-CH),
1
m.p. 59 °C; H NMR (CDCl3): δ ϭ 0.23 (s, 9 H, SiϪCH3), 1.04/ 18.7 (6 C, SiϪCHϪCH3), 22.7/22.7 (2 C, CH2), 70.9/71.2 (2 C,
1.05 (2 t, 2 ϫ 3 H, CH3), 1.80 (m, 4 H, CH2), 3.89/3.90 (2 t, 2 ϫ
OCH2), 96.5/99.8/101.2/102.9 (4 C, CϵC), 114.0/114.4 (2 Cq, C-1,
2 H, OCH2), 6.93 (s, 1 H, 3-H), 7.03 (s, 1 H, 6-H); 13C NMR C-4), 116.9/117.9 (2 C, C-3, C-6), 154.0/154.2 (2 Cq, C-2, C-5); FD
(CDCl3): δ ϭ 0.1 (3 C, SiϪCH3), 10.5/10.5 (2 C, CH3), 22.6/22.6 MS: m/z (%) ϭ 472.4 (16) [Mϩ], 471.5 (42) [Mϩ], 470.5 (100) [Mϩ];
(2 C, CH2), 71.3/71.6 (2 C, OCH2), 99.3 (1 C, ϵC-Si), 100.6 (1 C, IR (KBr): ν (cmϪ1) ϭ 2964, 2947, 2866, 2154, 1500, 1473, 1389,
˜
ArϪCϵ), 112.5/113.6 (2 Cq, C-1, C-4), 118.0/118.2 (2 C, C-3, C-
1224, 1203, 1045, 1025, 893, 858, 842; C28H46O2Si2 (470.9): calcd.
6), 149.3 (1 Cq, C-2), 154.7 (1 Cq, C-5); FD MS: m/z (%) ϭ 370.4 C 71.43, H 9.85; found C 71.38, H 9.85.
ϩ
ϩ
˜
(100) [M ], 368.5 (99) [M ]; IR (KBr): ν ϭ 2961, 2932, 2878, 2157,
1502, 1492, 1470, 1462, 1381, 1248, 1217, 1065, 1019, 883, 859,
840, 760, 679 cmϪ1; C17H25BrO2Si (369.2): calcd. C 55.28, H 6.82,
Br 21.63; found C 55.38, H 6.62, Br 21.41.
1-Ethynyl-2,5-dipropoxybenzene (16): Compound 9 (15.0 g, 0.05
mol) was stirred in a mixture of methanol (300 mL) and sodium
hydroxide (10.5 mL, c ϭ 5 mol/L) at room temperature for 48 h.
After evaporation of the solvent, the residue was dissolved in chlo-
roform and extracted with water and saturated NaHCO3. Drying
with Na2SO4, filtration, and removal of the solvent provided pure
product without further purification. Yield: 11.1 g (98%) of a
1-Bromo-2,5-dipropoxy-4-triisopropylsilylethynylbenzene (14): Com-
pound 8 (24.7 g, 0.062 mol) and a catalyst mixture of bis(tetraphen-
ylphosphane)palladium dichloride (1.1 g, 1.55 mmol), copper(I)
iodide (0.6 g, 3.1 mmol), and triphenylphosphane (0.8 g, 3.1 mmol)
were dissolved in dry piperidine (300 mL), and the system was
flushed with nitrogen. Triisopropylsilylacetylene (11.6 g, 0.064 mol)
was added to the clear solution in small portions. After the solution
had stirred for 12 h, the solvent was evaporated and chloroform
was added to the residue. The organic phase was extracted with
saturated NH4Cl, water, and saturated NaHCO3. Filtration
through a short silica gel column produced a solid, which was
recrystallized from 70 mL of 2-propanol. Yield: 24.0 g (85%), m.p.
1
slightly yellow oil; H NMR (CDCl3): δ ϭ 0.99/1.02 (2 t, 2 ϫ 3 H,
CH3), 1.80 (m, 4 H, CH2), 3.23 (s, 1 H, ϵCϪH), 3.83, 3.93 (2 t, 2
ϫ 2 H, OCH2), 6.77 (d, 1 H, 3-H), 6.82 (dd, 1 H, 4-H), 6.97 (d, 1
H, 6-H); 13C NMR (CDCl3): δ ϭ 10.4 (2 C, CH3), 22.6 (2 C, CH2),
70.2/71.1 (2 C, OCH2), 80.1 (1 C, ϵCϪH), 80.8 (1 C, ArϪCϵ),
112.3 (1 C, Cq-1), 113.9 (1 C, C-3), 117.0 (1 C, C-4), 119.3 (1 C,
C-6), 152.6/154.6 (2 C, C-2, C-5); FD MS: m/z (%) ϭ 217.9 (100)
ϩ
ϩ
˜
[M ], 218.9 (13) [M ]; IR (KBr): ν ϭ 3290, 2965, 2938, 2878, 1605,
1577, 1497, 1470, 1390, 1274, 1227, 1164, 1067, 1023, 981, 804
cmϪ1; C14H18O2 (218.3): calcd. C 77.03, H 8.31; found C 77.09,
H 8.30.
1
71 °C; H NMR (CDCl3): δ ϭ 1.02/1.04 (2 t, 2 ϫ 3 H, CH3), 1.12
(s, 21 H, SiϪCϪH, SiϪCϪCH3), 1.80 (m, 4 H, CH2), 3.87/3.91 (2
t, 2 ϫ 2 H, OCH2), 6.93 (s, 1 H, 3-H), 7.02 (s, 1 H, 6-H); 13C
NMR (CDCl3): δ ϭ 10.5 (2 C, CH3), 11.4 (3 C, Si-CH), 18.7 (6 C,
SiϪCϪCH3), 22.6 (2 C, CH2), 71.1/71.8 (2 C, OCH2), 95.6/102.5
(2 C, ArϪCϵC-Si), 113.0/113.5 (2 Cq, C-1, C-4), 117.8/118.6 (2 C,
C-3, C-6), 149.3 (1 Cq, C-2), 155.0 (1 Cq, C-5); FD MS: m/z (%) ϭ
1,4-Diethynyl-2,5-dipropoxybenzene (17). ؊ Preparation from 10:
Compound 10 (26.2 g, 0.068 mol) was dissolved in THF (100 mL),
and a mixture of methanol (100 mL) and sodium hydroxide (31
mL, c ϭ 5 mol/L) was added. After 5 min, the solvents were evap-
orated and the residue was washed several times with n-hexane.
Yield: 16.4 g (98%) of beige crystals. Ϫ Preparation from 11: Com-
pound 11 (6.2 g, 0.01 mol) was added to a mixture of THF (150
mL) and water (5 mL). Tetrabutylammonium fluoride (2.0 g, 0.013
mol) was added to the solution. After the mixture had been concen-
trated to 20% of its original volume, the residue was dissolved in
chloroform and extracted with water. The organic phase was dried
with Na2SO4 and filtered. The obtained oil was stirred in n-hexane
until crystallization of the solid was complete. Yield: 19.98 g (73%)
455.4 (27) [Mϩ], 454.4 (100) [Mϩ], 453.4 (26) [Mϩ], 452.4 (88)
ϩ
˜
[M ]; IR (KBr): ν ϭ 2985, 2943, 2865, 2158, 1502, 1470, 1460,
1382, 1270, 1215, 1045, 1021, 883, 855, 839, 768, 679 cmϪ1
;
C23H37BrO2Si (453.2): calcd. C 60.91, H 8.22; found C 60.94, H
8.23.
2,5-Dipropoxy-1-triisopropylsilylethynyl-4-trimethylsilyl-
ethynylbenzene (15). ؊ Preparation from 13: Compound 13 (12.0 g,
32.5 mmol), bis(tetraphenylphosphane)palladium dichloride (0.6 g,
0.83 mmol), copper(I) iodide (0.32 g, 0.17 mmol), triphenylphos-
phane (0.43 g, 0.17 mmol), and triisopropylsilylacetylene (6.5 g,
37.5 mmol) were dissolved in dry piperidine (230 mL), and the
system was flushed with nitrogen. After the solution had stirred for
3 d, the solvent was evaporated and chloroform was added to the
residue. The organic phase was extracted with saturated NH4Cl,
water, and saturated NaHCO3. Filtration through a short silica gel
column produced a brown solid, which was recrystallized from 100
mL of methanol. Yield: 13.0 g (82%) of yellow crystals. Ϫ Prepara-
tion from 14: Compound 14 (24.0 g, 53.0 mmol), bis(tetraphenyl-
1
of beige crystals, m.p. 122 °C; H NMR (CDCl3): δ ϭ 1.02 (t, 6 H
CH3), 1.80 (m, 4 H, CH2), 3.32 (s, 2 H, CϪH), 3.91 (t, 4 H, OCH2),
6.93 (s, 2 H, 3-H); 13C NMR (CDCl3): δ ϭ 10.4 (2 C, CH3), 22.5
(2 C, CH2), 71.1 (2 C, OCH2), 79.8 (2 C, ArϪCϵ), 82.5 (2 C,
ϵCϪH), 113.3 (2 Cq,C-1), 117.8 (2 C, C-3), 154.0 (2 Cq, C-2); EI
MS (70 eV): m/z (%) ϭ 243.3 (13) [Mϩ], 242.3 (75) [Mϩ], 158.2
(100) [Mϩ Ϫ 2C3H7]; IR (KBr): ν˜ ϭ 3270, 2958, 2912, 2878, 1501,
1469, 1392, 1223, 1099, 1040, 1021, 863, 799 cmϪ1; C16H18O2
(242.3): calcd. C 79.31, H 7.49; found C 79.20, H 7.38.
1-Bromo-4-ethynyl-2,5-dipropoxybenzene (18): Compound 13
phosphane)palladium dichloride (0.95 g, 1.35 mmol), copper(I) (12.8 g, 0.035 mol) was dissolved in methanol (350 mL) and sodium
iodide (0.5 g, 2.67 mmol), triphenylphosphane (0.7 g, 2.67 mmol), hydroxide (7.2 mL, c ϭ 5 mol/L). After the solution had stirred for
and trimethylsilylacetylene (5.9 g, 60.0 mmol) were dissolved in dry
piperidine (350 mL), and the system was flushed with nitrogen.
20 h, the solvent was evaporated and the residue was dissolved in
chloroform. Extraction with water and saturated NaHCO3 pro-
4438
Eur. J. Org. Chem. 2001, 4431Ϫ4443

Preparation and Nonlinear Optics of Monodisperse Oligo(1,4-phenyleneethynylene)s
FULL PAPER
vided, after drying and filtration, a black solid. Recrystallization
from methanol and afterwards from n-hexane produced the pure
tylene (6.9 g, 0.038 mol) were added to the mixture. After 20 h,
CH2Cl2 (200 mL) was added and the solution was extracted with
product. Yield: 8.2 g (80%) of yellow crystals, m.p. 86 °C; 1H NMR saturated NH4Cl, water, and saturated NaHCO3. Recrystallization
(CDCl3): δ ϭ 1.02/1.03 (2 t, 2 ϫ 3 H, CH3), 1.80 (m, 4 H, CH2), from methanol gave the pure product. Yield: 10.5 g (99%) of yellow
1
3.28 (s, 1 H, CϵCϪH), 3.90/3.91 (2 t, 2 ϫ 2 H, OCH2), 6.95 (s, 1 crystals, m.p. 70 °C; H NMR (CDCl3): δ ϭ 1.02 (m, 12 H, CH3),
H, 3-H), 7.06 (s, 1 H, 6-H); 13C NMR (CDCl3): δ ϭ 10.4/10.5 (2 1.12 (s, 21 H, SiϪCH, SiϪCϪCH3), 1.81 (m, 8 H, CH2), 3.91 (m,
C, CH3), 22.5/22.6 (2 C, CH2), 71.3/71.6 (2 C, OCH2), 79.5 (1 C, 8 H, OCH2), 6.80 (d, 2 H), 7.02 (d, 2 H), 7.01 (s, 1 H); 13C NMR
ArϪCϵ), 81.6 (1 C, ϵCϪH), 111.3/114.0 (2 Cq, C-1, C-4), 118.0/ (CDCl3): δ ϭ 10.5/10.6 (4 C, CH3), 11.4 (3 C, Si-CH), 18.7 (6 C,
118.4 (2 C, C-3, C-6), 149.3 (1 Cq, C-2), 154.7 (1 Cq, C-5); FD MS: SiϪCϪCH3), 22.8/22.8/22.9 (4 C, CH2), 70.7/71.4/72.0 (4 C,
m/z (%) ϭ 298.8 (13) [Mϩ], 297.8 (99) [Mϩ], 296.8 (15) [Mϩ], 295.8
OCH2), 90.4/91.9/96.8/103.8 (4 C, CϵC), 114.7/114.9/115.6 (3 Cq),
ϩ
˜
(100) [M ]; IR (KBr): ν ϭ 3279, 2958, 2911, 2878, 1491, 1460, 115.3/117.4/117.8/119.0/119.4 (5 C), 153.9/154.2/155.0/155.3 (4 Cq);
1381, 1218, 1040, 1020, 860, 831, 771 cmϪ1; C14H17BrO2 (297.2):
FD MS: m/z (%) ϭ 593.3 (11) [Mϩ], 592.3 (36) [Mϩ], 591.3 (100)
calcd. C 56.58, H 5.77, Br 26.89; found C 56.57, H 5.83, Br 26.58. [Mϩ]; IR (KBr): ν˜ ϭ 2964, 2942, 2865, 2152, 2064, 1498, 1468,
1390, 1220, 1024, 882, 859, 792, 770 cmϪ1; C37H54O4Si (590.9):
1-Ethynyl-2,5-dipropoxy-4-triisopropylsilylethynylbenzene
(19):
calcd. C 75.21, H 9.21; found C 75.38, H 9.13.
Compound 15 (25 g, 0.053 mol) was dissolved in a mixture of THF
(100 mL) and methanol (100 mL), and potassium carbonate (7.3 g, 1-(2,5-Dipropoxyphenylethynyl)-4-ethynyl-2,5-dipropoxybenzene
0.053 mol) was added. After 1 h, the solvent was evaporated and (22): Compound 21 (10.0 g, 0.017 mol) was dissolved in THF (50
the residue was dissolved in chloroform. The organic phase was
mL), and tetrabutylammonium fluoride (7.9 g, 0.025 mol) was ad-
extracted with water, dried with Na2SO4, and filtered, and finally ded. After 10 h, the solvent was evaporated and the residue was
the solvent was removed. The obtained oil was recrystallized from
dissolved in chloroform. Subsequent extraction with water and sat-
urated NaHCO3 gave a brown residue, which was purified by chro-
methanol. Yield: 13.7 g (65%) of yellow crystals, m.p. 92 °C; 1H
NMR (CDCl3): δ ϭ 1.01/1.03 (2 t, 2 ϫ 3 H, CH3), 1.12 (s, 21 H, matography on silica gel (toluene). Yield: 6.0 g (82%) of yellow
1
SiϪCH, SiϪCHϪCH3), 1.80 (m, 4 H, CH2), 3.30 (s, 1 H, crystals, m.p. 56 °C; H NMR (CDCl3): δ ϭ 1.03 (m, 12 H, CH3),
CϵCϪH), 3.88/3.93 (2 t, 2 ϫ 2 H, OCH2), 6.89 (s, 2 H, 3-H, 6-H); 1.79 (m, 8 H, CH2), 3.32 (s, 1 H, CϵCϪH), 3.92 (m, 8 H, OCH2),
13C NMR (CDCl3): δ ϭ 10.5/10.6 (2 C, CH3), 11.4 (3 C, Si-CH), 6.81 (m, 2 H), 6.97 (d, 2 H), 7.01 (m, 1 H); 13C NMR (CDCl3):
18.7 (6 C, SiϪCHϪCH3), 22.6/22.6 (2 C, CH2), 70.9/71.2 (2 C,
OCH2), 80.1 (1 C, ArϪCϵ), 82.1 (1 C, ϵCϪH), 96.7/102.7 (2 C, 70.2/71.1/71.3/71.4 (4 C, OCH2), 80.1 (1 C, ArϪCϵ), 82.1 (1 C,
ArϪCϵC-Si), 112.7/114.8 (2 Cq, C-1, C-4), 117.4/117.7 (2 C, C-3, ϵCϪH), 89.5/91.6 (2 C, ArϪCϵC-Ar), 112.4/113.9/115.4 (3 Cq),
C-6), 154.0/154.2 (2 Cq, C-2, C-5); FD MS: m/z (%) ϭ 400.5 (5) 116.7 (1 C), 117.2 (1 C, C-3), 118.2 (1 C, C-6), 118.7 (1 C), 152.9/
δ ϭ 10.4/10.5/10.6/10.6 (4 C, CH3), 22.6/22.6/22.7/22.8 (4 C, CH2),
ϩ
ϩ
ϩ
[M ], 399.4 (23) [M ], 398.4 (100) [M ]; IR (KBr): ν ϭ 3290, 2959, 153.3/154.0/154.1 (4 Cq); FD MS: m/z (%) ϭ 436.0 (26) [Mϩ], 435.0
˜
2943, 2866, 2150, 2063, 1500, 1473, 1390, 1219, 1045, 1022, 875,
(100) [Mϩ], 217.7 (1) [M2ϩ]; IR (KBr): ν˜ ϭ 3265, 2962, 2935, 2877,
856 cmϪ1; C25H38O2Si (398.7): calcd. C 75.32, H 9.61; found C 1505, 1473, 1426, 1383, 1271, 1236, 1203, 1132, 1065, 1044, 1024,
75.27, H 9.71.
983, 859, 811, 769, 713 cmϪ1; C28H34O4 (434.6): calcd. C 77.39, H
7.89; found C 77.11, H 7.73.
1-Bromo-2,5-dipropoxy-4-(2,5-dipropoxyphenylethynyl)benzene (20):
Compounds 8 (22.7 g, 57.0 mmol) and 16 (12.0 g, 55.0 mmol) were
4-(2,5-Dipropoxyphenylethynyl)-1-[2,5-dipropoxy-4-(triiso-
dissolved in dry piperidine (300 mL) and the system was flushed propylsilylethynyl)phenylethynyl]-2,5-dipropoxybenzene (23): Com-
with nitrogen. The catalyst mixture of bis(tetraphenylphosphane)- pounds 11 (7.7 g, 15.2 mmol) and 22 (6.0 g, 13.8 mmol) were dis-
palladium dichloride (0.97 g, 1.38 mmol), copper(I) iodide (0.52 g, solved in toluene (30 mL) and piperidine (10 mL) and the system
2.75 mmol), and triphenylphosphane (0.72 g, 2.75 mmol) was then
added. The reaction mixture was stirred for 12 h at room temper-
was flushed with nitrogen. A catalyst mixture of bis(tetraphenyl-
phosphane)palladium dichloride (0.25 g, 0.35 mmol), copper(I)
ature. The solvent was evaporated and the residue was dissolved in iodide (0.13 g, 0.70 mmol), and triphenylphosphane (0.18 g, 0.70
chloroform. The organic phase was extracted with saturated
NH4Cl, water, and saturated NaHCO3, then dried with Na2SO4
mmol) was added. The reaction was finished within 5 min, while
the temperature increased to 34 °C. Addition of 100 mL of CH2Cl2
and filtered. The solvent was evaporated. The crude product was was followed by extraction with saturated NH4Cl, water, and satur-
purified by chromatography on silica gel (toluene). Yield: 26.5 g ated NaHCO3. The crude product obtained was purified by chro-
1
(99%) of yellow crystals, m.p. 52 °C; H NMR (CDCl3): δ ϭ 1.05 matography on silica gel, firstly with toluene and secondly with
(m, 12 H, CH3), 1.80 (m, 8 H, CH2), 3.90 (m, 8 H, OCH2), 6.80 toluene/cyclohexane (1:1). Yield: 6.6 g (58%) of yellow crystals,
(dd, 2 H, 3Ј-H, 4Ј-H), 7.02 (d, 2 H, 6-H, 6Ј-H), 7.08 (s, 1 H, 3-H);
m.p. 77 °C; 1H NMR (CDCl3): δ ϭ 1.06 (m, 39 H, SiϪCH,
13C NMR (CDCl3): δ ϭ 10.5/10.5/10.6 (4 C, CH3), 22.6/22.7/22.8 SiϪCHϪCH3, CH3), 1.82 (m, 12 H, CH2), 3.92 (m, 12 H, OCH2),
(4 C, CH2), 70.2/71.4/71.5/71.5 (4 C, OCH2), 89.2/90.7 (2 C, CϵC), 6.81/6.81 (d, 2 H), 6.92/6.94 (2 s, 2 ϫ 1 H, 3-H, 6-H), 7.00 (m, 3
113.0/113.3/113.9 (3 Cq), 114.4/116.6/118.0/118.4/118.7 (5 CH),
H); 13C NMR (CDCl3): δ ϭ 10.6 (6 C, CH3), 11.4 (3 C, Si-CH),
149.5 (1 Cq, C-2), 152.9/154.0/154.0 (3 Cq); FD MS: m/z (%) ϭ 18.7 (6 C, SiϪCϪCH3), 22.7/22.8 (6 C, CH2), 70.2/70.8/71.2/71.4/
ϩ
ϩ
˜
490.7 (98) [M ], 488.7 (100) [M ]; IR (KBr): ν ϭ 2961, 2936, 2904,
71.4 (6 C, OCH2), 91.4/91.6/96.5/103.0 (6 C, CϵC), 114.0/114.4/
2877, 1604, 1505, 1464, 1426, 1379, 1272, 1209, 1067, 1027, 981, 116.8/118.0 (Cq), 116.6/117.5/118.6 (CH), 152.9/153.3/153.4/154.0/
858, 810, 769, 738 cmϪ1; C26H33BrO4 (489.5): calcd. C 63.80, H
6.80, Br 16.33; found C 63.95, H 6.78, Br 15.99.
154.3 (CqO); FD MS: m/z (%) ϭ 808.5 (67) [Mϩ], 807.5 (100) [Mϩ],
404.0 (4) [M2ϩ]; IR (KBr): ν ϭ 2964, 2941, 2866, 2149, 1501, 1417,
˜
1389, 1274, 1209, 1045, 1025, 980, 884, 859 cmϪ1; C51H70O6Si
(807.2): calcd. C 75.89, H 8.74; found C 75.43, H 8.88.
1-(2,5-Dipropoxyphenylethynyl)-2,5-dipropoxy-4-triisopropyl-
silylethynylbenzene (21): Compound 20 (9.2 g, 0.019 mol) was dis-
solved in toluene (20 mL) and piperidine (10 mL) and the system
1-(2,5-Dipropoxyphenylethynyl)-4-(4-ethynyl-2,5-dipropoxy-
was flushed with nitrogen. Bis(tetraphenylphosphane)palladium phenylethynyl)-2,5-dipropoxybenzene (24): Compound 23 (6.6 g,
dichloride (0.3 g, 0.48 mmol), copper(I) iodide (0.2 g, 0.95 mmol), 8.2 mmol) was dissolved in THF (50 mL) and tetrabutylammonium
triphenylphosphane (0.25 g, 0.95 mmol), and triisopropylsilylace-
fluoride (3.9 g, 12.3 mmol) was added. The solvent was evaporated
4439
Eur. J. Org. Chem. 2001, 4431Ϫ4443

H. Meier, D. Ickenroth, U. Stalmach, K. Koynov, A. Bahtiar, C. Bubeck
FULL PAPER
and the residue taken up in CH2Cl2 (100 mL). After extraction
with water, the organic phase was dried with Na2SO4 and filtered,
IR (KBr): ν
˜ ϭ 2963, 2940, 2866, 2149, 1509, 1468, 1423, 1387,
1273, 1213, 1064, 1017, 986, 884, 861 cmϪ1; C65H85O8BrSi
and the solvents were evaporated. The obtained orange crystals (1102.4): calcd. C 70.82, H 7.77; found C 70.84, H 7.78.
were purified by column chromatography on silica gel (toluene).
1-[4-(2,5-Dipropoxyphenylethynyl)-2,5-dipropoxyphenylethynyl]-4-
[2,5-dipropoxy-4-(2,5-dipropoxy-4-triisopropylsilylethynyl-
phenylethynyl)phenylethynyl]-2,5-dipropoxybenzene (27): Com-
Yield: 4.8 g (90%) of yellow crystals, m.p. 97 °C; 1H NMR
(CDCl3): δ ϭ 1.03 (m, 18 H, CH3), 1.85 (m, 12 H, CH2), 3.34 (s,
1 H, ϵCϪH), 3.90 (m, 12 H, OCH2), 6.81/6.82 (d, 2 ϫ 1 H), 6.96/
pounds 16 (1.0 g, 4.58 mmol) and 26 (1.6 g, 1.48 mmol) were dis-
7.00/7.01/7.02 (m, 5 ϫ 1 H); 13C NMR (CDCl3): δ ϭ 10.5/10.5/
solved in toluene (5 mL) and piperidine (3 mL) and the system was
10.6/10.6 (6 C, CH3), 22.6/22.7/22.8 (6 C, CH2), 70.2/71.1/71.2/71.2/
71.4 (6 C, OCH2), 80.1 (1 C, ArϪCϵ), 82.3 (1 C, ϵCϪH), 89.8/
91.1/91.7 (4 C, ArϪCϵC-Ar), 112.6/114.0/114.8/115.1 (Cq), 114.4/
116.6/117.2/117.5/118.1/118.7 (CH), 152.9/153.3/153.4/153.5/154.0/
flushed with nitrogen. To this solution were added bis(tetraphenyl-
phosphane)palladium dichloride (0.052 g, 0.074 mmol), copper(I)
iodide (0.007 g, 0.037 mmol), and triphenylphosphane (0.010 g,
0.037 mmol). The black solution was stirred for 16 h at 60 °C and
154.1 (CqO); FD MS: m/z (%) ϭ 652.3 (40) [Mϩ], 651.3 (100) [Mϩ],
for 2 h at 80 °C. CH2Cl2 (100 mL) was added to the cooled mixture,
325.8 (3) [M2ϩ]; IR (KBr): ν ϭ 3265, 2961, 2937, 2877, 1510, 1429,
˜
which was extracted with saturated NH4Cl, water, and saturated
NaHCO3. The crude product was purified by column chromato-
graphy on silica gel (toluene/CH2Cl2, 9:1). Yield: 1.53 g (84%) of
1274, 1211, 1044, 1025, 984, 864, 810, 772 cmϪ1; C42H50O6 (650.9):
calcd. C 77.51, H 7.74; found C 77.61, H 7.62.
1
yellow crystals, m.p. 140 °C; H NMR (CDCl3): δ ϭ 1.05 (m, 51
1,4-Bis(4-bromo-2,5-dipropoxyphenylethynyl)-2,5-dipropoxybenzene
(25): Compounds 8 (19.0 g, 0.048 mol) and 17 (4.8 g, 0.020 mol)
were dissolved in dry piperidine (240 mL) and the system was
flushed with nitrogen. To this clear and slightly brown solution
were added bis(tetraphenylphosphane)palladium dichloride (0.4 g,
0.50 mmol), copper(I) iodide (0.3 g, 1.58 mmol), and triphenylphos-
phane (0.3 g, 1.14 mmol). After 30 min, the reaction was complete
and the piperidine was evaporated. The residue was taken up in
chloroform (200 mL) and extracted with saturated NH4Cl, water,
and saturated NaHCO3. The obtained residue was then filtered
with chloroform through silica gel. The crude product was purified
twice by column chromatography on silica gel (toluene/n-hexane
2:1). Yield: 8.0 g (52%) of ochre crystals, m.p. 95 °C; 1H NMR
(CDCl3): δ ϭ 1.06 (m, 18 H, CH3), 1.82 (m, 12 H, CH2), 3.95 (m,
12 H, OCH2), 7.00/7.01/7.08 (3 s, 3 ϫ 2 H); 13C NMR (CDCl3):
δ ϭ 10.5 (6 C, CH3), 22.6/22.6/22.7 (6 C, CH2), 71.3/71.5/71.6 (6
C, OCH2), 90.6/90.9 (4 C, CϵC), 113.1/113.4/114.4 (Cq), 117.6/
118.0/118.5 (CH), 149.5 (Cq), 153.5/154.1 (2 Cq); FD MS: m/z
(%) ϭ 788.4 (17) [M ϩ 1]ϩ, 787.3 (100) [Mϩ], 786.3 (25) [Mϩ],
H, SiϪCH, SiϪCHϪCH3, CH3), 1.84 (m, 20 H, CH2), 3.93 (m, 20
H, OCH2), 6.81 (d, 2 H), 6.93/6.94 (2 s, 2 ϫ 1 H), 7.01 (d, 7 H);
13C NMR (CDCl3): δ ϭ 10.5/10.6 (10 C, CH3), 11.4 (3 C, Si-CH),
18.7 (6 C, SiϪCϪCH3), 22.7/22.8 (10 C, CH2), 70.2/70.8/71.2/71.4/
71.4 (10 C, OCH2), 89.8/91.4/91.6/91.6/91.6/91.7/96.6/103.0 (10 C,
CϵC), 114.0/114.1/114.4/114.7 (Cq), 116.8/117.4/117.5/118.0/118.6
(CH), 152.9/153.3/153.5/154.0/154.3 (CqO); FD MS: m/z (%) ϭ
1243.0 (13) [M ϩ 1]ϩ, 1242.0 (69) [Mϩ], 1241.1 (54) [Mϩ], 1240.0
(100) [Mϩ], 620.9 (23) [M2ϩ], 620.3 (39) [M2ϩ], 414.4 (1) [M3ϩ],
413.7 (3) [M3ϩ]; IR (KBr): ν ϭ 2964, 2939, 2867, 2149, 1511, 1470,
˜
1425, 1388, 1273, 1211, 1064, 1017, 987, 884, 861 cmϪ1
;
C79H102O10Si (1239.8): calcd. C 76.54, H 8.29; found C 76.41, H
8.40.
1-[4-(2,5-Dipropoxyphenylethynyl)-2,5-dipropoxyphenylethynyl]-4-
[4-(2,5-dipropoxy-4-ethynylphenylethynyl)phenylethynyl]-2,5-
dipropoxybenzene (28): Compound 27 was dissolved in THF (20
mL) and tetrabutylammonium fluoride (0.5 g, 1.65 mmol) was ad-
ded. After 20 min, the solvent was evaporated and the residue was
dissolved in CH2Cl2. The organic phase was extracted with water,
dried with Na2SO4, and filtered. The solvent was then removed and
the orange residue was purified by column chromatography on sil-
ica gel, using CH2Cl2 as starting eluent and changing continuously
until pure toluene was reached. The resulting yellow powder was
washed several times with cyclohexane. Yield: 1.15 g (94%) of yel-
ϩ
ϩ
˜
785.3 (63) [M ], 784.3 (21) [M ]; IR (KBr): ν ϭ 2966, 2935, 2906,
2877, 1500, 1471, 1423, 1374, 1268, 1220, 1046, 1022, 986, 907,
856, 827, 778, 748 cmϪ1; C40H48Br2O6 (784.6): calcd. C 61.23, H
6.12; found C 61.27, H 6.12.
1-[4-(4-Bromo-2,5-dipropoxyphenylethynyl)-2,5-dipropoxy-
phenylethynyl]-4-[2,5-dipropoxy-4-(triisopropylsilylethynyl)-
phenylethynyl]-2,5-dipropoxybenzene (26): Compounds 19 (3.6 g,
9.0 mmol) and 25 (3.0 g, 3.8 mmol) were dissolved in toluene (100
mL) and piperidine (50 mL) and the system was flushed with nitro-
gen. To this solution were added bis(tetraphenylphosphane)pallad-
ium dichloride (0.13 g, 0.19 mmol), copper(I) iodide (0.07 g,
0.38 mmol), and triphenylphosphane (0.10 g, 0.38 mmol). The mix-
ture was stirred for 6 h at 60 °C and the volume was reduced to
20%. The residue was taken up in CH2Cl2 (200 mL) and extracted
with saturated NH4Cl, water, and saturated NaHCO3. Purification
was achieved with column chromatography on silica gel, first with
toluene/cyclohexane (1:1) and afterward with toluene as eluent.
Yield: 2.1 g (39%) of yellow crystals, m.p. 124 °C; 1H NMR
(CDCl3): δ ϭ 1.05 (m, 45 H, SiϪCH, SiϪCHϪCH3, CH3), 1.82
1
low crystals, m.p. 152 °C; H NMR (CDCl3): δ ϭ 1.05 (m, 30 H,
CH3), 1.84 (m, 20 H, CH2), 3.33 (s, 1 H, ϵC-H), 3.93 (m, 20 H,
OCH2), 6.81 (d, 2 H), 6.98 (m, 11 H); 13C NMR (CDCl3): δ ϭ
10.4/10.6 (10 C, CH3), 22.6/22.7/22.8 (10 C, CH2), 70.2/71.1/71.2/
71.4 (10 C, OCH2), 80.1/82.3/89.8/91.2/91.4/91.5/91.6/91.7/92.5 (10
C, CϵC), 112.6/114.3/114.4/114.4/114.5/114.7/115.1 (Cq), 117.2/
117.4/117.5/118.1/118.7 (CH), 152.9/153.3/153.5/154.0/154.1 (CqO);
FD MS: m/z (%) ϭ 1085.9 (24) [M ϩ 1]ϩ, 1084.9 (100) [Mϩ], 1083.9
(54) [Mϩ], 543.2 (13) [M2ϩ], 542.6 (17) [M2ϩ], 542.1 (53) [M2ϩ],
361.6 (1) [M3ϩ]; IR (KBr): ν ϭ 3290, 2965, 2937, 2877, 2104, 1512,
˜
1472, 1427, 1388, 1274, 1211, 1064, 1044, 1022, 985, 863, 770, 714
cmϪ1; C70H82O10 (1083.4): calcd. C 77.60, H 7.63; found C 77.41,
H 7.60.
(m, 16 H, CH2), 3.94 (m, 16 H, OCH2), 6.92/6.94/7.00/7.08 (8 H); 1-(2,5-Dipropoxyphenylethynyl)-2,5-dipropoxybenzene (1a): Com-
13C NMR (CDCl3): δ ϭ 10.4 (8 C, CH3), 11.4 (3 C, Si-CH), 18.6
pounds 6 (0.73 g, 2.3 mmol) and 16 (0.45 g, 2.1 mmol) were dis-
(6 C, SiϪCϪCH3), 22.5/22.6/22.6/22.7 (8 C, CH2), 70.9/71.2/71.4/ solved in dry piperidine (15 mL) and the system was flushed with
71.5/71.6 (8 C, OCH2), 90.5/90.8/91.2/91.5/96.4/103.0 (8 C, CϵC), nitrogen. The catalysts bis(tetraphenylphosphane)palladium
113.1/113.3/114.2/114.4/114.5 (Cq), 116.9/117.5/117.9/118.1/118.4
dichloride (0.05 g, 0.07 mmol), copper(I) iodide (0.03 g,
(CH), 149.5/153.3/153.5/154.0/154.3 (CqO); FD MS: m/z (%) ϭ 0.016 mmol), and triphenylphosphane (0.05 g, 0.019 mmol) were
1105.8 (31) [M ϩ 1]ϩ, 1104.7 (75) [Mϩ], 1103.8 (100) [Mϩ], 1102.8 added one after another. After 4 d, the mixture was filtered through
(49) [Mϩ], 1101.8 (69) [Mϩ], 552.0 (16) [M2ϩ], 551.2 (17) [M2ϩ]; silica gel with ethyl acetate and the solvent was removed. The crude
4440
Eur. J. Org. Chem. 2001, 4431Ϫ4443

Preparation and Nonlinear Optics of Monodisperse Oligo(1,4-phenyleneethynylene)s
product was purified by column chromatography on silica gel (tolu-
[M ϩ 1]ϩ, 844.5 (75) [Mϩ], 843.4 (100) [Mϩ], 422.1 (4) [M2ϩ]; IR
FULL PAPER
1
˜
ene). Yield: 0.63 g (74%) of yellow needles, m.p. 51 °C; H NMR (KBr): ν ϭ 2965, 2932, 2875, 1512, 1466, 1430, 1386, 1271, 1209,
(CDCl3): δ ϭ 1.01, 1.06 (2 t, 12 H, CH3), 1.77 (m, 8 H, CH2), 3.86, 1065, 1042, 1022, 980, 864, 815, 769, 730 cmϪ1; C54H66O8 (843.1):
3.97 (2 t, 8 H, OCH2), 6.98 (d, 2 H, 6-H), 6.80 (m, 4 H, 3-H, 4-
H); 13C NMR (CDCl3): δ ϭ 10.5, 10.6 (each 2 C, CH3), 22.7, 22.8
(each 2 C, CH2), 70.2, 71.5 (each 2 C, OCH2), 89.8 (2 C, CϵC),
114.3 (2C, C-1), 114.5 (2C, C-3), 116.4 (2C, C-4), 118.7 (2C, C-6),
152.9 (2C, C-2), 154.0 (2 C, C-5); EI MS (70 eV): m/z (%) ϭ 410
(100) [Mϩ], 367 (7) [Mϩ ϪC3H7], 205 (5) [M2ϩ], 43 (39) [C3H7ϩ];
IR (KBr): ν˜ ϭ 2966, 2935, 2878, 1502, 1469, 1435, 1389, 1270,
1193, 1002, 977, 875, 809 cmϪ1; C26H34O4 (410.6): calcd. C 76.06,
H 8.35; found C 76.04, H 8.34.
calcd. C 76.93, H 7.89; found C 77.02, H 7.91.
1,4-Bis[4-(2,5-dipropoxyphenylethynyl)-2,5-dipropoxyphenyl-
ethynyl]-2,5-dipropoxybenzene (1d). ؊ Preparation from 17 and 20:
Compounds 17 (0.5 g, 2.06 mmol) and 20 (2.3 g, 2.54 mmol) were
dissolved in piperidine (100 mL) and the system was flushed with
nitrogen. Bis(tetraphenylphosphane)palladium dichloride (0.07 g,
0.10 mmol), copper(I) iodide (0.04 g, 0.21 mmol), and triphenyl-
phosphane (0.05 g, 0.21 mmol) were added to the solution. The
reaction mixture was stirred for 5 d at 40 °C. The piperidine was
1,4-Bis(2,5-dipropoxyphenylethynyl)-2,5-dipropoxybenzene
(1b): evaporated and the residue was taken up in 100 mL of CH2Cl2.
Compounds 6 (0.51 g, 1.14 mmol) and 17 (0.5 g, 2.3 mmol) were
dissolved in dry piperidine and the system was flushed with nitro-
gen. To this yellow solution were added bis(tetraphenylphosphane)-
The organic phase was extracted with saturated NH4Cl, water, and
saturated NaHCO3. The crude product was purified by column
chromatography on silica gel (toluene). Yield: 1.6 g (76%) of yellow
palladium dichloride (0.06 g, 0.085 mmol), copper(I) iodide (0.05 g, crystals. Ϫ Preparation from 8, 17, and 16: In this two-step reaction,
0.26 mmol), and triphenylphosphane (0.06 g, 0.23 mmol). The re- compounds 8 (3.01 g, 7.55 mmol) and 17 (0.91 g, 3.78 mmol) were
action was complete within 5 d and the mixture was filtered dissolved in dry piperidine (100 mL) and the system was flushed
through silica gel with CH2Cl2. The obtained brown oil was puri- with nitrogen. Bis(tetraphenylphosphane)palladium dichloride
fied by column chromatography on silica gel (toluene). Yield: 0.65 g (0.2 g, 0.29 mmol), copper(I) iodide (0.1 g, 0.53 mmol), and tri-
1
(91%) of yellow crystals, m.p. 98 °C; H NMR (CDCl3): δ ϭ 1.01,
1.07 (2 t, 12 H, CH3), 1.81 (m, 12 H, CH2), 3.86 (t, 4 H, OCH2), Completion of the reaction was detected by TLC after 3 h and
3.96, 3.98 (2 t, 8 H, OCH2), 6.81, 6.82 (2 s, 4 H), 7.03 (s, 2 H), 7.01 the ethynyl component 16 (1.8 g, 8.25 mmol) was added. After an
phenylphosphane (0.01 g, 0.38 mmol) were added to the solution.
(s, 2 H); 13C NMR (CDCl3): δ ϭ 10.40, 10.46, 10.5 (each 2 C, additional 12 h, the solvent was removed and the residue was dis-
CH3), 22.59, 22.65, 22.7 (each 2 C, CH2), 70.2 (2 C, OCH2), 71.2, solved in a small amount of CH2Cl2. Methanol was added until
71.4 (each 2 C, OCH2), 89.9 (2 C, Ar-CC), 91.3 (2 C, Ar-CC), 114.1 precipitation was finished. The obtained product was purified twice
(2 C), 114.5 (4 C), 116.5 (2 C), 117.7 (2 C), 118.7 (2 C), 152.9, by column chromatography on silica gel, the first time with toluene/
153.5, 154.0 (CqO); FD MS: m/z (%) ϭ 627 (100) [Mϩ]; IR (KBr): chloroform (9:1) as eluent, and the second time toluene. Yield:
ν ϭ 2966, 2933, 2873, 1497, 1473, 1390, 1275, 1221, 1047, 1024,
0.61 g (15%) of yellow crystals, m.p. 147 °C; 1H NMR (CDCl3):
˜
874, 858, 796 cmϪ1; C40H50O6 (626.8): calcd. C 76.65, H 8.04; δ ϭ 1.05 (m, 30 H, CH3), 1.83 (m, 20 H, CH2), 3.86, t, 4 H/3.98,
found C 76.70, H 7.95.
m, 16 H, (OCH2), 6.81 (d, 4 H, 3-H, 4-H), 7.02 (m, 8 H); 13C NMR
(CDCl3): δ ϭ 10.5/10.6/10.6 (10 C, CH3), 22.6/22.7/22.8 (10 C,
CH2), 70.2/71.2/71.2/71.4 (10 C, OCH2), 89.8 (2 C), 91.4/91.5/91.6
(6 C), 113.9/114.0/114.3/114.6 (8 Cq), 114.2 (2 C), 116.6 (2 C), 117.3
(2 C), 117.4 (4 C), 118.5 (2 C, C-6), 152.8/153.3/153.4/153.9 (CqO);
FD MS: m/z (%) ϭ 1061.9 (6) [Mϩ], 1059.9 (20) [Mϩ], 1059.0 (100)
[Mϩ], 530.4 (29) [M2ϩ], 529.4 (60) [M2ϩ], 352.9 (8) [M3ϩ]; IR
1-(2,5-Dipropoxyphenylethynyl)-4-[4-(2,5-dipropoxyphenylethynyl)-
2,5-dipropoxyphenylethynyl]-2,5-dipropoxybenzene (1c). ؊ Prepara-
tion from 20 and 22: Compounds 20 (1.35 g, 2.76 mmol) and 22
(1.2 g, 2.76 mmol) were dissolved in dry piperidine (150 mL) and
the system was flushed with nitrogen. To this clear solution were
added bis(tetraphenylphosphane)palladium dichloride (0.01 g,
0.053 mmol), copper(I) iodide (0.01 g, 0.038 mmol), and triphenyl-
phosphane (0.01 g, 0.038 mmol). When the reaction was complete,
the solvent was evaporated and the residue was taken up in chloro-
˜
(KBr): ν ϭ 2964, 2936, 2876, 1513, 1472, 1429, 1388, 1272, 1211,
1065, 1042, 1023, 987, 863, 814, 770, 725 cmϪ1; C68H82O10
(1059.4): calcd. C 77.10, H 7.80; found C 77.10, H 7.84.
form. The organic phase was extracted with saturated NH4Cl, 1-[4-(2,5-Dipropoxyphenylethynyl)-2,5-dipropoxyphenylethynyl]-4-
water, and saturated NaHCO3. The crude product was purified by
column chromatography on silica gel (toluene). Yield: 0.13 g (6%)
{4-[4-(2,5-dipropoxyphenylethynyl)-2,5-dipropoxyphenylethynyl]-2,5-
dipropoxyphenylethynyl}-2,5-dipropoxybenzene (1e): Compounds 6
of yellow crystals. Ϫ Preparation from 6 and 24: Compounds 6 (0.6 g, 1.85 mmol) and 28 (1.0 g, 0.92 mmol) were dissolved in tolu-
(0.98 g, 3.07 mmol) and 24 (1.0 g, 1.54 mmol) were dissolved in ene (12 mL) and piperidine (5 mL), and the system was flushed
toluene (10 mL) and piperidine (2 mL) and the system was flushed with nitrogen. To enhance the solubility, the temperature was raised
with nitrogen. Bis(tetraphenylphosphane)palladium dichloride to 60 °C. After the catalyst mixture of bis(tetraphenylphosphane)-
(0.027 g, 0.038 mmol), copper(I) iodide (0.015 g, 0.077 mmol) and palladium dichloride (0.016 g, 0.023 mmol), copper(I) iodide
triphenylphosphane (0.02 g, 0.077 mmol) were added to the solu-
tion. The reaction was complete after 10 min and CH2Cl2 (100
(0.009 g, 0.046 mmol), and triphenylphosphane (0.012 g,
0.046 mmol) had been added, the reaction was stirred for 1 h. After
mL) was added, followed by extraction of the organic phase with removal of the solvent, the residue was taken up in CH2Cl2 (50
saturated NH4Cl, water, and saturated NaHCO3. The crude prod- mL) and extracted with saturated NH4Cl, water, and saturated
uct was purified by column chromatography on silica gel (toluene) NaHCO3. The crude product was purified by column chromato-
and subsequently washed with cyclohexane. Yield: 0.3 g (23%) of graphy on silica gel (toluene). Yield: 0.8 g (68%) of yellow crystals,
yellow crystals with m.p. 117 °C Ϫ 1H NMR (CDCl3): δ ϭ 1.01 (t,
m.p. 181 °C; 1H NMR (CDCl3): δ ϭ 1.05 (m, 36 H, CH3), 1.84
6 H)/1.07 (m, 18 H) (CH3), 1.82 (m, 16 H, CH2), 3.86 (t, 4 H)/3.97 (m, 24 H, CH2), 3.87 (t, 4 H)/3.99 (m, 20 H) (OCH2), 6.81 (d, 4
(m, 4 H) (OCH2), 6.81 (d, 4 H), 7.01 (s, 4 H), 7.02 (d, 2 H); 13C H), 7.01 (m, 10 H); 13C NMR (CDCl3): δ ϭ 10.4/10.5 (12 C, CH3),
NMR (CDCl3): δ ϭ 10.5/10.6/10.6 (8 C, CH3), 22.6/22.7/22.8 (8 C, 22.6/22.7/22.8 (12 C, CH2), 70.3/71.3/71.5 (12 C, OCH2), 89.8 (2
CH2), 70.2/71.2/71.2/71.4 (8 C, OCH2), 89.6/92.2 (6 C, CϵC), C), 91.4/91.6 (8 C, CϵC), 114.2/114.3/114.5/114.9 (Cq), 114.6 (2
114.2/114.3/114.8 (6 Cq), 114.6/116.6 (4 C), 117.4/117.5 (4 C), 118.5 C), 116.7 (2 C), 117.7 (4 C), 117.8 (4 C), 118.8 (2 C), 153.0/153.6/
(2 C), 152.9/153.5/153.6/154.1 (CqO); FD MS: m/z (%) ϭ 845.5 (13)
154.1 (CqO); FD MS: m/z (%) ϭ 1278.9 (20) [M ϩ 1]ϩ, 1277.9 (37)
Eur. J. Org. Chem. 2001, 4431Ϫ4443
4441

H. Meier, D. Ickenroth, U. Stalmach, K. Koynov, A. Bahtiar, C. Bubeck
FULL PAPER
[11]
[Mϩ], 1276.8 (100) [Mϩ], 1275.9 (95) [Mϩ], 639.7 (10) [M2ϩ], 638.8
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[12]
(78) [M2ϩ], 638.1 (63) [M2ϩ], 426.2 (4) [M3ϩ], 425.2 (12) [M3ϩ]; IR
˜
(KBr): ν ϭ 2964, 2936, 2876, 1512, 1471, 1427, 1388, 1273, 1211,
[13]
1065, 1020, 985, 863, 805, 768, 722 cmϪ1; C82H98O12 (1275.7):
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[14]
THG Measurements: Thin films for the nonlinear optical studies
were prepared in the following way: Compounds 1a؊e were mixed
with polystyrene (MW ϭ 100.000) at (10.00 Ϯ 0.03)% of concentra-
tion by weight, dissolved in toluene using a concentration by weight
of the mixture of 2.7%, and spincast on fused silica substrates at
spinning speeds of 500 rpm and 9000 rpm. This resulted in final
film thicknesses d of the order of 212 nm and 50 nm, respectively,
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model PL 2143B), the second harmonic output of which pumped
a parametric generator (EKSPLA model PG 501), which gave laser
pulses with a duration of 20 ps, repetition rate 10 Hz, and a wave-
length tuning range between 680 nm and 2000 nm. The laser beam
was focused on the sample, which was mounted on a rotation stage
and positioned in an evacuated chamber. We measured the Maker
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Eur. J. Org. Chem. 2001, 4431Ϫ4443

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FULL PAPER
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Received June 29, 2001
[O01317]
Eur. J. Org. Chem. 2001, 4431Ϫ4443
4443