Branched oligothiophene silanes with the efficient nonradiative energy transfer between the fragments

Article abstract of DOI:10.1007/s11172-010-0164-6

The synthesis of new dendrimers and branched oligothiophene silanes containing bithiophene groups at the periphery and quaterthiophene fragments at the center of the molecule is described. Specific features of bithiophene silane bromination were shown, and the conditions for the efficient synthesis of methyltris(5-bromo-2,2′-bithiophen-5-yl)silane have been found for the first time. The optical properties of the synthesized compounds were studied. The efficiency of the electron excitation energy transfer between the fragments of branched bi-and quaterthiophene silanes was measured.

Full text of DOI:10.1007/s11172-010-0164-6

Russian Chemical Bulletin, International Edition, Vol. 59, No. 4, pp. 797—805, April, 2010
797
Branched oligothiophene silanes with the efficient nonradiative
energy transfer between the fragments
O. V. Borshchev, S. A. Ponomarenko, E. A. Kleymyuk, Yu. N. Luponosov, N. M. Surin, and A. M. Muzafarov
N. S. Enikolopov Institute of Synthetic Polymeric Materials, Russian Academy of Sciences,
70 ul. Profsoyuznaya, 117393 Moscow, Russian Federation.
Fax: +7 (495) 335 9000. Eꢀmail: ponomarenko@ispm.ru
The synthesis of new dendrimers and branched oligothiophene silanes containing
bithiophene groups at the periphery and quaterthiophene fragments at the center of the
molecule is described. Specific features of bithiophene silane bromination were shown, and the
conditions for the efficient synthesis of methyltris(5ꢀbromoꢀ2,2´ꢀbithiophenꢀ5ꢀyl)silane have
been found for the first time. The optical properties of the synthesized compounds were studied.
The efficiency of the electron excitation energy transfer between the fragments of branched biꢀ
and quaterthiophene silanes was measured.
Key words: oligothiophene silane dendrimers, bromination of bithiophene silanes, molecuꢀ
lar antennas, nonradiative energy transfer.
Reports on the synthesis and study of the properties of
the luminescent polymers1,2 and dendrimers3,4 appear
presently with increasing frequency. Among the latter, sysꢀ
tems with the nonradiative transfer of the electron excitaꢀ
tion energy between different fragments of the macromolꢀ
ecule are of great interest. Since the ordered close arrangeꢀ
ment of fluorescent fragments with appropriate spectral
properties is possible within the same dendrimer macroꢀ
molecule, one can obtain systems with the efficient transꢀ
fer of the energy absorbed by many peripheral fragments
to the center of fluorescence emission with a certain waveꢀ
length. Such dendritic systems are often named molecular
antennas.5,6
The dendrimers in which the monothiopene fragments
are at the periphery and the bithiopene (2T) fragments
directly bound to the silicon atoms are located at the cenꢀ
ter of the macromolecule have been described earlier.7,8
The dendrimers synthesized had the fluorescence specꢀ
trum similar to that of the 2T fragments and the absorpꢀ
tion spectrum corresponding to the sum of the absorption
spectra of the monoꢀ and bithiophene fragments. Howevꢀ
er, no efficient energy transfer between the monoꢀ and
bithiophene fragments of the macromolecule was observed.
Recently we synthesized9 the dendrimer and branched oliꢀ
gothiophene silane containing the 2T groups at the peꢀ
riphery and terthiophene (3T) fragments at the center of
the molecule. In these organosilicon systems, the pheꢀ
nomenon of nonradiative electron excitation energy transꢀ
fer from the biꢀ to terthiopene fragments has been obꢀ
served for the first time. The efficiency of the energy transꢀ
fer was 97 and 91%, for the dendrimer and branched oligoꢀ
thiophene silane, respectively. The study of the optical
properties of the dendrimers and branched oligothiophene
silanes consisting of the monoꢀ, biꢀ, and terthiophene fragꢀ
ments showed8,9 no πꢀconjugation between the chroꢀ
mophore fragments linked by the silicon atom. The abꢀ
sence of πꢀconjugation makes it possible to consider the
oligothiophene silane dendrimers as systems of structuralꢀ
ly organized and weakly interacting chromophore fragꢀ
ments. The nonradiative electron excitation energy transꢀ
fer between the fragments of such a system occurs due to
the inductive resonance interaction. The calculation of
the electron excitation energy transfer from the biꢀ to terꢀ
thiophene fragments by the Förster—Galanin formulas10,11
gave good coincidence with experiment in the case of both
the bi/terthiophene silane dendrimer and the correspondꢀ
ing branched bi/terthiophene silane. Such systems can be
considered as "active light filters" shifting the spectrum of
the light passing through the filters by its reꢀemission in
a longerꢀwavelength range. However, difference in the
spectra of biꢀ and terthiopene in the earlier studied comꢀ
pounds are not too large (50 nm between the absorption
maxima and 43 nm between the fluorescence maxima).
On the one hand, this provides the efficient energy transꢀ
fer between the fragments considered; on the other hand,
this results in a small shift between the absorbed and reꢀ
emitted light. The problem of extending the spectra range
of such systems is urgent for both the estimation of the
transfer efficiency in macromolecules with a large spectral
shift between the luminophores and their practical use.
The purpose of the present work is the synthesis and
study of the regularities of the electron excitation energy
transfer between the fragments of dendrimer 1 and branꢀ
ched oligothiophene silane 2 containing the bithiophene
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 781—789, April, 2010.
1066ꢀ5285/10/5904ꢀ0797 © 2010 Springer Science+Business Media, Inc.

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Borshchev et al.

Branched oligothiophene silanes
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 4, April, 2010
799
groups at the periphery and the quaterthiophene (4T) fragꢀ
ments at the center of the macromolecule. Methyltrisꢀ
(5´ꢀhexylꢀ2,2´ꢀbithiophenꢀ5ꢀyl)silane (3) and methylꢀ
tris(5´´´ ꢀhexylꢀ2,2´:5´,2″:5″,2´´´ ꢀquaterthiophenꢀ5ꢀyl)ꢀ
silane (4), being structural analogs of the fragments of
the macromolecules considered, were used as objects for
comparison.
The lithium derivative obtained reacted with the ethereal
complex of magnesium dibromide MgBr2•Et2O to form
the Grignard reagent. The interaction of the latter with
2ꢀbromothiophene under the Kumada reaction conditions
afforded 2,2´ꢀbithiophenꢀ5ꢀyl(trimethyl)silane (6) in 89%
yield. Then compound 6 was lithiated to position 5´ with
nꢀbutyllithium at –70 °C to form the lithium derivative,
which was further reacted with methyltrichlorosilane with
the formation of methyltris(5ꢀtrimethylsilylꢀ2,2´ꢀbithioꢀ
phenꢀ5´ꢀyl)silane (7) in 90% yield. Chromatographically
pure compound 7 was isolated by column chromatograꢀ
phy in 60% yield (Fig. 1, a).
In the next reaction, NBS was used as a brominating
agent, which is often applied for the selective substitution
of protons of oligothiophenes in positions 2(5) for bromine
atoms.13 The replacement of the trimethylsilyl groups in
oligothiophenes and their derivatives by iodine atoms usꢀ
ing iodine chloride is also described.14 However, to the
best of our knowledge, NBS has not earlier been used for
the substitution of the trimethylsilyl groups for bromine in
oligothiophenes. Moreover, as can be seen from the strucꢀ
tural formula, two silicon atoms can be distinguished in
compound 7: external silicon atoms bound to three methꢀ
yl groups and one bithiophene fragment and the internal
silicon atom having one methyl group and three biꢀ
thiophene fragments. In our opinion, this is the difference
in environment which results in selective bromination with
Results and Discussion
Dendrimer 1 and branched oligothiophene silane 2
were synthesized by the reactions of organoboron derivaꢀ
tives of thiophene silane monodendrons with bromo deꢀ
rivatives having the branched and linear structures followꢀ
ing the Suzuki reaction similar to the scheme7—9 used by
us earlier for the preparation of other oligothiophene silꢀ
ane dendrimers.
In the case of dendrimer 1, the branching center was
methyltris(5´ꢀbromoꢀ2,2´ꢀbithiophenꢀ5ꢀyl)silane (5),
which was not described earlier. An attempt of the syntheꢀ
sis of such a compound according to the procedure used
for the preparation of the trifunctional monothiophene
silane branching center from 5ꢀbromoꢀ2ꢀthienyllithium7
was unsuccessful. Therefore, a basically new approach was
proposed (Scheme 1). First, 2ꢀthienyl(trimethyl)silane was
synthesized in 76% yield using the described procedure.12
Then it was lithiated with nꢀbutyllithium to position 5.
Scheme 1
dppf is diphenylphosphinoferrocene, NBS is Nꢀbromosuccinimide

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Russ.Chem.Bull., Int.Ed., Vol. 59, No. 4, April, 2010
Borshchev et al.
the complete replacement of the external trimethylsilyl
groups by bromine atom, remaining uninvolved the bonds
between the central silicon atom and surrounding three
bithiophene fragments.
The second necessary component for the synthesis of
the dendrimer and branched oligothiophene silane is the
organoboron derivative of thiophene silane monodendron.
Compounds 8 and 9 were used as the second components
for the synthesis of the dendrimer and branched oligoꢀ
thiophene silane, respectively. Details of the synthesis of
these compounds have been described earlier.8,9 Dendrimꢀ
er 1 was synthesized by the reaction of compound 5 with
20% excess of compound 8 by the Suzuki reaction (Scheme 2,
route a). According to the GPC data, 37% of target denꢀ
drimer 1 were formed upon refluxing for 90 h. The purifiꢀ
cation by preparative GPC allowed us to isolate dendrimꢀ
er 1 in the pure form in 18% yield.
Commercially available 5,5´ꢀdibromoꢀ2,2´ꢀbithioꢀ
phene was used as a bromo derivative in the synthesis of
branched oligothiophene silane 2 (Scheme 2, route b).
After the completion of the Suzuki reaction, the reaction
mixture contained 36% of branched oligothiophene silane
2, according to the GPC analysis data. Purification
by column chromatography gave the pure product in
21% yield.
Due to rather high difference in sizes of the trimethylꢀ
silyl group and bromine atom (which results in a substanꢀ
tial difference in hydrodynamic radii of all intermediate
and final bromination products), the reaction course was
monitored by GPC. After three hours from the beginning
of the synthesis, the reaction mixture contained 21% of
intermediate product I with one bromine atom, 43% of
intermediate product II with two bromine atoms, and 36%
of trisubstituted product III (Fig. 1, b). The further occurꢀ
rence of the reaction increased the content of reaction
product III and decreased the amount of the intermediꢀ
ates (Fig. 1, c). According to the GPC data, the final
reaction mixture contained 93% of the final product and
7% of the intermediate (Fig. 1, d). After column chroꢀ
matography, pure compound 5 was isolated in 79% yield.
It can be asserted on the basis of the data obtained that
the bromination of compound 7 proceeds step by step
with the replacement of one trimethylsilyl group, then
of the second group, and finally of the third trimethylꢀ
silyl group.
The details of the synthesis of branched bithiophene
silane 3 have been described previously.15 The lithiation of
5ꢀhexylꢀ2,2´ꢀbithiophene with nꢀbutyllithium followed by
Scheme 2

Branched oligothiophene silanes
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 4, April, 2010
801
I (arb. units)
I (arb. units)
1.0
a
c
III
1.0
II
0.8
0.6
0.4
0.2
0.8
0.6
0.4
0.2
I
6
8
t/min
6
8
t/min
I (arb. units)
I (arb. units)
d
b
1.0
II
1.0
0.8
0.6
0.4
0.2
0.8
0.6
0.4
0.2
III
I
6
8
t/min
6
8
t/min
Fig. 1. GPC curves: compound 7 after purification (a), the reaction mixture after 3 h (b), 6 h (c), and the end of the reaction (d); I, II,
and III are the monoꢀ, biꢀ, and trisubstituted products, respectively; Phenogel 500 Å column, diode matrix as the detector, λ = 254 nm.
the exchange of lithium for the organoboron residue afꢀ
forded16 compound 10 in 96% yield. It was used in the
Suzuki reaction with trifunctional branching center 5 to
form branched quaterthiophene silane 4 (Scheme 3). Afꢀ
ter 68ꢀh reflux, the yield was 85%. Purification was carried
out by column chromatography and recrystallization. The
yield of chromatographically pure compound 4 was 53%.
The structure and purity of intermediate and final comꢀ
NMR spectra of all synthesized compounds contained all
characteristic signals. The integral intensities of signals of
protons at different structural fragments corresponded to
the theoretically calculated values (see Experimental).
To study the optical properties of compounds 1 and 2,
the absorption and fluorescence spectra of their dilute soꢀ
lutions were measured. The fluorescence quantum yield
was determined by comparison with the known quantum
yields of the standards using the method of measuring
fluorescence of dilute solutions.17 Solutions of the folꢀ
1
pounds were confirmed by GPC analysis, H, 13C, and
29Si NMR spectroscopy, and elemental analysis. The
Scheme 3
IPTMDOB is 2ꢀisopropoxyꢀ4,4,5,5ꢀtetramethylꢀ1,3,2ꢀdioxaborolane

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Russ.Chem.Bull., Int.Ed., Vol. 59, No. 4, April, 2010
Borshchev et al.
I (arb. units)
1.0
lowing compounds were used as standards: pꢀterphenyl
(ΦF = 0.90), 2,5ꢀdiphenyloxazole (PPO, ΦF = 0.91), anꢀ
thracene (ΦF = 0.27), 1,4ꢀdi(5ꢀphenyloxazolꢀ2ꢀyl)benzene
(POPOP, ΦF = 0.98), and rhodamine 6G (ΦF = 0.94).
The quantum yield values of compounds 1 and 2 given
in the present work are average, calculated with allowꢀ
ance for measurements relatively to each of five standards.
In order to calculate the efficiency of the electron exꢀ
1´
2´
1
0.8
0.6
0.4
0.2
4´
2
4T), we used the meaꢀ
2T
→
citation energy transfer (QETE
sured absorption and fluorescence spectra obtained upon
the excitation with the light with the wavelength λ2T;4T
3´
3
,
at which both the 2T and 4T fragments absorb the light,
and with the light with the wavelength λ4T, at which
only the 4T fragments absorb. The fraction of the light
absorbed by the 2T and 4T fragments in the region
of overlap of their absorption spectra was determined
by the decomposition of the total absorption spectrum
to the components taking into account the spectral
shape of the absorption bands of compounds 3 and 4. The
procedure of calculation of the efficiency of the electron
excitation energy transfer between the fragments of the
dendrite macromolecule and approaches of using absorpꢀ
tion spectra of the model compounds have been described
earlier.9
The absorption and fluorescence spectra of dilute soꢀ
lutions of compounds 1 and 2 in THF, as well as the
fluorescence spectra of biꢀ and quaterthiophene silanes 3
and 4, respectively, in the absence of electron excitation
energy transfer are shown in Figs 2 and 3. It is well seen
that the fluorescence spectra of compounds 1 and 2 coinꢀ
cide with the fluorescence spectrum of quaterthiophene
silane 4 upon excitation at the absorption band maxima of
both quaterthiophene (416 and 410 nm) and bithiophene
(333 nm) fragments.
300 350 400 450 500 550 600
λ/nm
Fig. 3. Absorption (1—3) and fluorescence (1´—4´) spectra of
compounds 2, 3, and 4 in THF: the absorption of compound 2
(1) and bithiophene (2) and quaterthiophene fragments (3); the
fluorescence of compound 2 at λ = 333 (1´) and 410 nm (2´)
exc
and of compounds 3 (3´) and 4 (4´).
absorbed by the bithiophene fragments to the quaterꢀ
thiophene fragments. The integral fluorescence intensity
divided into the absorption coefficient of the exciting radiꢀ
ation is somewhat lower upon excitation to the absorption
region of the bithiophene fragments than upon the excitaꢀ
tion of only the quaterthiophene fragments. Therefore,
the energy transfer efficiency is lower than 100%. The
calculations taking into account the fraction of radiation
absorbed by the biꢀ and quaterthiophene fragments give
the efficiency of the transfer equal to 94 and 85% for comꢀ
pounds 1 and 2, respectively.
The results obtained by the study of the optical properꢀ
ties of dilute molecular solutions of compounds 1—4 in
THF are listed in Table 1.
It seems interesting to compare the obtained data with
the results of studying the optical properties of the denꢀ
drimer and branched oligothiophene silane containing the
bithiophene fragments at the periphery and the terꢀ
thiophene fragments at the center of the macromolecule.9
As in the macromolecules with the biꢀ and terthiophene
fragments and in the compounds with the biꢀ and quaterꢀ
thiophene, the molar absorption coefficients of the correꢀ
sponding bands are equal to the sum of the absorption
coefficients of the fragments. In the both cases, the fluꢀ
orescence quantum yield of the fragments, which are enerꢀ
gy acceptors, corresponds to that of the respective to model
compound. The spectral distribution of fluorescence phoꢀ
tons upon the excitation of both the donating fragments
and the fragments acting as energy acceptors corresponds
to the fluorescence spectrum of the corresponding energy
acceptor. The efficiency of the energy transfer in the sysꢀ
tems with the quaterthiophene fragments as an energy
acceptor is by 3—4% lower than that in the systems with
the terthiophene fragments. Probably, this is due to the
larger length of the quaterthiophene fragments, because
the efficiency of the transfer following the dipoleꢀdipole
Thus, the character of fluorescence of the synthesized
compounds indicates the efficient transfer of the energy
I (arb. units)
1
1.0
0.8
0.6
0.4
0.2
4´
2´
2
1´
3´
3
300 350 400 450 500 550 600
λ/nm
Fig. 2. Absorption (1—3) and fluorescence (1´—4´) spectra of
compounds 1, 3, and 4 in THF: the absorption of compound 1
(1) and bithiophene (2) and quaterthiophene fragments (3); the
fluorescence of compound 1 at λ = 333 (1´) and 416 nm (2´)
exc
and of compounds 3 (3´) and 4 (4´).

Branched oligothiophene silanes
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 4, April, 2010
803
Table 1. Results of studying the optical properties* of the synthesized compounds
abs
fl
Comꢀ
pound
λ
max/nm
ε•10–3
QF
(%)
λ
max/nm
QETE
(%)
/L mol–1 cm–1
1
334 1
416 1
126 9
138 10
12 2
13 2
470 1.5
496 1.5
537 1.5
468 1.5
496 1.5
534 1.5
384 1.5
469 1.5
94 3
—
—
87 3
—
—
2
333 1
408 1
80 7
48 4
11 2
13 2
3
4
332 1
412 1
61 6
138.3 10
19 3
13 2
—
—
abs
fl
* λ max and λ max are the wavelengths of the absorption and fluorescence maxima.
column (USA) 7.8×300 mm in size packed with the Phenogel
sorbent with the pore size 500 Å, THF as the eluent).
mechanism depends substantially on the distance between
the energy donor and acceptor.
Absorption and luminescence spectra were measured in
a range of 200—600 nm in dilute THF solutions with the conꢀ
centration 10–5—10–6 mol L–1 to avoid selfꢀabsorption. Absorpꢀ
tion spectra were recorded on a Shimadzu UVꢀ2501PC spectroꢀ
photometer (Japan). An ALS01M multifunctional adsorption
luminescence spectrometer was used for the measurement of
luminescence. The threeꢀchannel optical system was used in the
spectrometer for the synchronous measurement of electronic
absorption, excitation and luminescence (fluorescence or phosꢀ
phorescence) spectra of the samples. The high sensitivity to low
concentrations of luminescent substances was achieved by the
use of the method of single photon counting in successive time
intervals with an automated control of the measured radiaꢀ
tion intensity.
So, its can be assumed that the synthesized compounds
and those studied earlier9 are molecular dendritic antennas
with the efficient electron excitation energy transfer folꢀ
lowing the Förster—Galanin mechanism. Therefore, in
the synthesis of the oligothiophene silanes, one can beꢀ
forehand estimate the efficiency of the energy transꢀ
fer between the fragments using for this purpose the
Förster—Galanin expression and the spectral data for the
compounds modeling the corresponding energy donors and
acceptors of the fragments of the system.
Thus, in the present work we synthesized for the first
time dendrimer 1 and branched oligothiophene silane 2
containing the bithiophene fragments at the periphery and
the quaterthiophene fragments at the center of the macroꢀ
molecule, as well as starꢀlike quaterthiophene silane 4.
The new scheme for the synthesis of the bromo derivatives
of bithiophene silanes by the replacement of the trimethꢀ
ylsilyl groups by Nꢀbromosuccinimide was developed. The
efficient energy transfer from the peripheral group of
the dendritic molecules to the internal groups was deꢀ
monstrated.
All reactions, if not otherwise stated, were carried out unꢀ
der an inert atmosphere and in anhydrous solvents. The solꢀ
vent was removed by evacuation (down to 1 Torr) on heating
to 40 °C.
2ꢀThienyl(trimethyl)silane was synthesized from thiophene
(38.11 g, 0.453 mol), a 2.5 М solution of BuLi in hexane (151 mL,
0.377 mol), and trimethylchlorosilane (41.08 g, 0.377 mol)
according to an earlier described procedure.12 According to
the GPC analysis, after the end of the reaction the mixture
contained 82% of the product. Pure 2ꢀthienyl(trimethyl)silane
(45 g, 76%) was isolated after distillation, b.p. 165—168 °C
1
(748 Torr). H NMR (CDCl3), δ: 0.32 (s, 9 H, Me3Si); 7.19
Experimental
(dd, 1 H, H(4), J1 = 3.1 Hz, J2 = 4.3 Hz); 7.27 (dd, 1 H, H(5),
J1 = 1.2 Hz, J2 = 3.1 Hz); 7.60 (dd, 1 H, H(3), J1 = 4.3 Hz,
J2 = 1.2 Hz).
Solutions of butyllithium in hexane (1.6 and 2.5 mol L–1),
thiophene, 2ꢀbromothiophene, Nꢀbromosuccinimide, and 5,5´ꢀ
dibromoꢀ2,2´ꢀbithiophene (Acros), as well as 2ꢀisopropoxyꢀ
4,4,5,5ꢀtetramethylꢀ1,3,2ꢀdioxaborolane (IPTMDOB) and tetꢀ
rakis(triphenylphosphine)palladium(0) Pd(PPh3)4 (Aldrich),
were used as received. Methyltrichlorosilane and trimethylchloꢀ
rosilane were distilled prior to use; THF and diethyl ether were
preꢀdried over calcium hydride and dehydrated by distillation
over lithium aluminum hydride.
1Н NMR spectra were recorded on a Bruker WPꢀ250 SY
spectrometer (250.13 MHz) using Me4Si as the internal standꢀ
ard. 13C and 29Si NMR spectra were obtained on a Bruker
DRX500 spectrometer. GPC analysis was carried out on a Shiꢀ
madzu instrument (Japan), a RIDꢀ10A refractometer and an
SPDꢀM10AVP diode matrix served as detectors (Phenomenex
2,2´ꢀBithiophenꢀ5ꢀyl(trimethyl)silane (6). Tetrahydrofuran
(70 mL) was added dropwise to a 2.5 M solution (30.71 mL) of
BuLi in hexane (75.8 mmol), maintaining the temperature beꢀ
low –10 °С. Then a solution of 2ꢀthienyl(trimethyl)silane (12 g,
75.8 mmol) in THF (90 mL) was added slowly, maintaining the
temperature in the interval from –10 to 0 °С. An ethereal soluꢀ
tion of the complex of magnesium bromide with ether (freshly
prepared from magnesium (2.32 g, 97 mmol) and dibromoetꢀ
hane (8 mL, 92 mmol) in 40 mL of anhydrous ether) was poured
to the obtained lithium derivative. The resultant Grignard reꢀ
agent was added dropwise to a solution of the Pd(dppf)Cl2 cataꢀ
lyst (0.17 g, 0.23 mmol) and 2ꢀbromothiophene (12.51 g, 77
mmol) in THF (150 mL) at 0—10 °С. After heating to ~20 °C,
the reaction mixture was stirred for 2 h. According to the GPC

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Borshchev et al.
analysis, after the standard isolation the reaction mixture conꢀ
tained 89% of the product. The purification was carried out by
column chromatography with silica gel (hexane as the eluent)
followed by distillation in vacuo. Pure compound 6 was obtained
off. The product was purified by column chromatography (toꢀ
luene as the eluent) followed by recrystallization from a toluꢀ
ene—hexane (1 : 2) mixture. Pure dendrimer 1 was isolated in
a yield of 0.186 g (18%). 1Н NMR (DMSO—CCl4), δ: 0.87
(t, 18 H, J = 6.7 Hz); 0.92 (s, 9 H); 0.94 (s, 3 H); 1.22—1.42
(m, 36 H); 1.62 (m, 12 H, J = 7.3 Hz); 2.73 (t, 12 H, J = 7.3 Hz);
6.69 (d, 6 H, J = 3.7 Hz); 7.04 (d, 6 H, J = 3.7 Hz); 7.16—7.27
(m, 18 Н); 7.28—7.43 (m, 18 Н). 13C NMR (CDCl3), δ: –0.27;
–0.20; 14.10; 22.56; 28.72; 30.14; 31.52; 31.54; 123.97; 124.34;
124.37; 124.40; 124.83; 124.93; 125.05; 125.08; 125.12; 132.77;
133.78; 134.24; 134.39; 135.74; 135.92; 136.18; 136.34; 137.85;
137.99; 143.96; 144.19; 145.18; 145.95. 29Si NMR (CDCl3), δ:
–25.28, –25.13. Found (%): С, 61.79; H, 5.29; S, 28.83; Si,
4.23. C136H138S24Si4. Calculated (%): С, 61.54; H, 5.24; S, 28.99;
Si, 4.23.
5,5´´´ꢀBis[bis(5´ꢀhexylꢀ2,2´ꢀbithiophenylꢀ5ꢀyl)(methyl)siꢀ
lyl]ꢀ2,2´:5´,2″:5″,2´´´ꢀquaterthiophene (2). The synthesis was
carried out similarly to the previous procedure from compound 9
(0.45 g, 0.6 mmol), 5,5´ꢀdibromoꢀ2,2´ꢀbithiophene (0.085 g,
0.26 mmol), and Pd(PPh3)4 (35 mg, 0.03 mmol). The reaction
mixture was refluxed for 86 h and poured into a separatory funꢀ
nel containing toluene (50 mL) and water (100 mL). The organꢀ
ic layer was washed to the neutral pH of the medium and dried
over Na2SO4, and the solvent was evaporated. The product was
purified by column chromatography (toluene—hexane (1 : 5)
mixture as the eluent). Pure compound 2 was isolated in a yield
of 0.078 g (21%). 1Н NMR (CDCl3), δ: 0.88 (t, 12 H, J = 6.7 Hz);
0.93 (s, 6 H); 1.21—1.41 (m, 24 H); 1.66 (m, 8 H, J = 7.3 Hz);
2.77 (t, 8 H, J = 7.3 Hz); 6.66 (d, 4 H, J = 3.7 Hz); 7.01 (d, 4 H,
J = 3.7 Hz); 7.05 (d, 2 H, J = 3.7 Hz); 7.10 (d, 2 H, J = 3.7 Hz);
7.18 (d, 4 Н, J = 3.7 Hz); 7.24—7.33 (m, 8 H). 13C NMR
(CDCl3), δ: –0.20; 14.09; 22.56; 28.72; 30.14; 31.52; 31.54;
123.97; 124.34; 124.82; 124.95; 125.07; 132.78; 134.24; 134.38;
135.88; 136.23; 137.84; 143.98; 145.18; 145.95. 29Si NMR
(CDCl3), δ: –25.27. Found (%): С, 62.98; H, 5.85; S, 27.04;
Si, 4.00. C74H82S12Si2. Calculated (%): С, 62.93; H, 5.85;
S, 27.24; Si, 3.98.
1
in a yield of 12.03 g (67%). Н NMR (DMSO—CCl4), δ: 0.31
(s, 9 Н, Me3Si); 7.02 (dd, 1 H, H(4´), J1 = 3.7 Hz, J2 = 5.5 Hz);
7.13 (d, 1 H, H(4), J = 3.7 Hz); 7.20 (dd, 1 Н, H(3´), J1 = 1.2 Hz,
J2 = 3.7 Hz); 7.23 (d, 1 H, H(3), J = 3.7 Hz); 7.34 (dd, 1 H,
H(5´), J1 = 1.2 Hz, J2 = 5.5 Hz). 13C NMR (CDCl3), δ: 0.36;
124.25; 124.83; 125.49; 128.24; 135.16; 137.89; 140.23; 142.88.
29Si NMR (CDCl3), δ: –6.37. Found (%): С, 55.38; H, 6.01;
S, 26.98; Si, 11.58. C11H14S2Si. Calculated (%): С, 55.41; H, 5.92;
S, 26.89; Si, 11.78.
Methyltris(5ꢀtrimethylsilylꢀ2,2´ꢀbithiophenꢀ5´ꢀyl)silane (7).
A 2.5 M solution (5 mL) of butyllithium in hexane was added
dropwise to a solution of compound 6 (3.12 g, 0.013 mol) in
THF (50 mL), maintaining the temperature below –55 °С. Then
the temperature was increased to 0 °С, the mixture was cooled to
–75 °С, after which methyltrichlorosilane (0.47 mL, 0.004 mol)
was poured, and the mixture was stirred for 30 min at –73 °С.
According to the GPC analysis, the reaction mixture contained
90% of silane 7. To isolate this compound, the mixture was
poured to 200 mL of iceꢀcold water and 300 mL of freshly disꢀ
tilled diethyl ether. The organic layer was washed with distilled
water (3×100 mL), dried over sodium sulfate, and concentrated
on a rotary evaporator. The purification was carried out by colꢀ
umn chromatography with silica gel (toluene—hexane (1 : 10)
mixture as the eluent). Pure compound 7 was obtained in a yield
1
of 1.74 g (58%). Н NMR (DMSO—CCl4), δ: 0.30 (s, 27 Н);
0.95 (s, 3 Н); 7.15 (d, 3 Н, H(3), J = 3.7 Hz); 7.30 (d, 3 Н, H(4),
J = 3.7 Hz); 7.32 (d, 3 Н, H(4´), J = 3.7 Hz); 7.34 (d, 3 H,
H(3´), J = 3.7 Hz). 13C NMR (CDCl3), δ: 0.32; 0.36; 125.64;
126.01; 134.31; 135.21; 138.34; 140.87; 142.38; 145.04. 29Si NMR
(CDCl3), δ: –25.18, –6.29. Found (%): С, 54.09; H, 5.68;
S, 25.64; Si, 14.78. C34H42S6Si4. Calculated (%): С, 54.06; H, 5.60;
S, 25.47; Si, 14.87.
Methyltris(5´ꢀbromoꢀ2,2´ꢀbithiophenꢀ5ꢀyl)silane (5). To
a solution of compound 7 (1.00 g, 1.32 mmol) in DMF NBS
(1.06 g, 5.9 mmol) was added in the dark at 0—10 °С. After the
end of the reaction, the reaction mixture was poured to a mixꢀ
ture of iceꢀcold water (100 mL) and freshly distilled diethyl ether
(100 mL). The organic layer was washed with distilled water
(3×100 mL), dried over sodium sulfate, concentrated on a rotaꢀ
ry evaporator, and purified by column chromatography (toluꢀ
ene—hexane (1 : 5) mixture as the eluent). After purification the
product was isolated in a yield of 0.810 g (79%). 1Н NMR
(CDCl3), δ: 0.96 (s, 3 Н); 6.96 (d, 3 Н, H(3), J = 3.7 Hz); 6.98
(d, 3 Н, H(4), J = 3.7 Hz); 7.16 (d, 3 Н, H(4´), J = 3.7 Hz); 7.31
(d, 3 H, H(3´), J = 3.7 Hz). 13C NMR (CDCl3), δ: 0.12; 112.12;
124.90; 125.85; 131.17; 134.45; 138.38; 138.77; 144.07. 29Si NMR
(CDCl3), δ: –25.01. Found (%): С, 38.77; H, 1.92; Br, 30.77;
S, 24.73; Si, 3.64. C25H15Br3S6Si. Calculated (%): С, 38.72;
H, 1.95; Br, 30.91; S, 24.81; Si, 3.62.
Methyltris(5´ꢀhexylꢀ2,2´:5´,2″:5″,2´´´ꢀquaterthienꢀ5ꢀyl)ꢀ
silane (4). The synthesis was carried out similarly to the proceꢀ
dure of synthesis of compound 1 from compound 10 (0.80 g,
2.12 mmol), compound 5 (0.42 g, 0.55 mmol), and Pd(PPh3)4
(125 mg, 0.11 mmol). The reaction mixture was refluxed for
68 h, after which anhydrous toluene was added and a toluꢀ
ene—water azeotropic mixture was distilled off. The product was
purified by column chromatography (toluene as the eluent) and
recrystallization. Pure compound 4 was isolated in a yield of
1
0.37 g (53%). Н NMR (CDCl3), δ: 0.88 (t, 9 H, J = 6.7 Hz);
0.96 (s, 3 Н); 1.23—1.43 (m, 18 H); 1.67 (m, 6 H, J = 7.3 Hz);
2.79 (t, 6 H, J = 7.3 Hz); 6.67 (d, 3 H, J = 3.7 Hz); 6.96 (d, 3 H,
J = 3.7 Hz); 6.98 (d, 3 H, J = 3.7 Hz); 7.04 (d, 6 H, J = 3.7 Hz);
7.11 (d, 3 H, J = 3.7 Hz); 7.26 (d, 3 H, J = 3.7 Hz); 7.33 (d, 3 H,
J = 3.7 Hz). Found (%): С, 61.64; H, 5.18; S, 30.03. C67H66S12Si.
Calculated (%): C, 62.67; H, 5.18; S, 29.96.
Methyltris{5´ꢀ[methylbis(5´ꢀhexylꢀ2,2´ꢀbithiophenꢀ5ꢀyl)ꢀ
silyl]ꢀ2,2´:5´,2″:5″,2´´´ꢀquaterthiophenꢀ5´´´ꢀyl}silane (1). Soluꢀ
tions of compound 8 (1.04 g, 1.25 mmol) and compound 5 (0.269 g,
0.35 mmol) in toluene (30 mL) and a 2 M solution of Na2CO3
(1.9 mL) were poured into a flask containing Pd(PPh3) (72 mg,
0.06 mmol), and the mixture was heated to boiling. The reaction
mixture was refluxed for 90 h, anhydrous toluene (30 mL) was
added, and a toluene—water azeotropic mixture was distilled
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 07ꢀ03ꢀ
01037a), the Russian Federal Agency on Science and Inꢀ
novations (Contract 02.513.12.3101), and the Council on
Grants of the President of the Russian Federation (Proꢀ
gram for State Support of Young Candidates of Sciences,
Grant MKꢀ129.2009.3).

Branched oligothiophene silanes
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Received May 7, 2009;
in revised form January 25, 2010