Self-assembly and semiconductivity of an oligothiophene supergelator

Article abstract of DOI:10.3762/bjoc.6.122

A bis(trialkoxybenzamide)-functionalized quaterthiophene derivative was synthesized and its self-assembly properties in solution were studied. In non-polar solvents such as cyclohexane, this quaterthiophene π-system formed fibril aggregates with an H-type

Full text of DOI:10.3762/bjoc.6.122

Self-assembly and semiconductivity
of an oligothiophene supergelator
Pampa Pratihar1, Suhrit Ghosh1,2, Vladimir Stepanenko1,
Sameer Patwardhan3, Ferdinand C. Grozema3, Laurens D. A. Siebbeles3
and Frank Würthner*1
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2010, 6, 1070–1078.
1Universität Würzburg, Institut für Organische Chemie, 97074
Würzburg, Germany, 2Indian Association for the Cultivation of
Science, Polymer Science Unit, Kolkata-700032, India (present
address) and 3Opto-Electronic Materials Section, Delft Chem Tech,
Delft University of Technology, Julianalaan 136, 2628 BL Delft, The
Netherlands
doi:10.3762/bjoc.6.122
Received: 15 June 2010
Accepted: 05 August 2010
Published: 16 November 2010
Guest Editor: J.-P. Desvergne
Email:
Frank Würthner* - wuerthner@chemie.uni-wuerzburg.de
© 2010 Pratihar et al; licensee Beilstein-Institut.
License and terms: see end of document.
* Corresponding author
This work is dedicated to Prof. Henning Hopf on the occasion of his
70th birthday.
Keywords:
charge transport; hydrogen bonding; oligothiophene; organogel;
self-assembly
Abstract
A bis(trialkoxybenzamide)-functionalized quaterthiophene derivative was synthesized and its self-assembly properties in solution
were studied. In non-polar solvents such as cyclohexane, this quaterthiophene π-system formed fibril aggregates with an H-type
molecular arrangement due to synergistic effect of hydrogen bonding and π-stacking. The self-assembled fibres were found to
gelate numerous organic solvents of diverse polarity. The charge transport ability of such elongated fibres of quaterthiophene
π-system was explored by the pulse radiolysis time resolved microwave conductivity (PR-TRMC) technique and moderate mobility
values were obtained. Furthermore, initial AFM and UV-vis spectroscopic studies of a mixture of our electron-rich quaterthiophene
derivative with the electron acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) revealed a nanoscale segregated assembly
of the individual building blocks in the blend.
Introduction
Self-assembly provides a spontaneous pathway to generate ing various functional π-systems has attracted much interest in
higher-order structures from suitably designed building blocks the recent past due to their potential applications as active
by virtue of specific intra and intermolecular non-covalent inter- components in a variety of organic electronic devices [2].
actions [1]. The development of such building blocks contain- Organogels are a special class of self-assembled materials in
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Beilstein J. Org. Chem. 2010, 6, 1070–1078.
which small building blocks generate fibrous structures due to [20] were synthesized from commercially available starting ma-
intermolecular non-covalent interactions, and these elongated terials in a few synthetic steps by literature methods, and then
fibres form interpenetrating network in which the solvent mole- coupled together to produce the thiophene-containing building
cules are trapped [3,4]. Organogels based on various π-systems block 6 in 78% yield. 2, 2´-Bithiophene was converted to the
such as oligophenylenevinylenes [5] and thienylenevinylenes corresponding tributyltin derivative 8 by the reported procedure
[6] oligophenyleneethylenes [7], phthalocyanines [8], por- [19] and then coupled with compound 6 in the presence of a
phyrins [9], naphthalene and perylene bisimides [10-12], acenes Pd-catalyst to give the desired oligothiophene derivative T1 in
[13,14] and merocyanines [15,16] have been studied in recent 82% yield. The new compounds 6 and T1 were characterized
years. Self-assembly of various oligothiophene derivatives have by 1H NMR and UV-vis spectroscopy, HRMS (ESI) and
been extensively investigated on account of their semicon- elemental analysis, while those synthetic intermediates already
ducting and optoelectronic properties [17]. Feringa and reported in the literature were characterized by 1H NMR and
co-workers reported organogels based on bisurea derivatives of UV-vis spectroscopy.
bithiophene chromophores and demonstrated a significant
charge carrier mobility as a result of self-assembly (Σμmin = 5 × Gelation tests
10−3 cm2 V−1 s−1) [18]. However, the building blocks were The gelation properties of T1 were examined in various organic
made only from mono and bithiophene units. Later, Shinkai and solvents (Table 1) at a concentration of 3.5 mM. At room
co-workers reported the gelation ability of quaterthiophene and temperature T1 was soluble only in chloroform, dichloro-
hexathiophene derivatives with peripheral amide-linked choles- methane, and tetrahydrofuran among other tested solvents.
terol moieties [19]. We recently reported [12] the self-assembly However, at elevated temperatures this quaterthiophene could
of perylene bisimide (PBI) π-systems that are functionalized be dissolved in all the tested solvents and when the hot solution
with trialkoxybenzamide moiety and have shown that they pos- was cooled down to room temperature, spontaneous gelation
sess much superior and versatile gelation and self-assembly was observed (see Figure 1A, inset) in most cases within 5–10
properties compared to those of cholesterol-linked PBI gelators minutes. For example, aromatic hydrocarbons (toluene,
reported earlier [10]. We also have demonstrated that the benzene), aliphatic hydrocarbons (methylcyclohexane, cyclo-
trialkoxybenzamide units provide a unique opportunity to tune hexane, n-heptane, n-hexane), chlorinated hydrocarbons
the mode of self-assembly (H-type vs. J-type) of PBIs by (chlorobenzene, tetrachloroethylene, 1,2-dichloroethane), ethers
systematically varying the steric crowding in the peripheral (dibutyl ether, THF, dioxan), hydrogen-bonding donor mole-
alkyl groups [20,21]. These recent findings on PBI gelators cules (triethylamine, acetone), and even highly polar solvents
prompted us to explore the utility of similar supramolecular such as DMF and ethanol could be gelated with T1. The only
design on the self-assembly of other functional π-systems.
exceptions were acetonitrile and DMSO for which no gelation
was observed. Critical gelation concentrations (CGC) were
Herein we describe the synthesis, self-assembly, gelation, and determined for all the solvents gelated with T1 and found to be
charge-carrier mobility studies of trialkoxybenzamide-function- below 0.3 wt %. This CGC value is much lower compared to
alized quaterthiophene derivative T1 (Scheme 1). We also those of the previously reported quaterthiophene gelators con-
present our initial results on the morphology of blends of this taining cholesteryl amide peripheral groups [19]. It is interest-
electron-rich p-type semiconducting T1 with the well-known ing to note that in aliphatic hydrocarbons (methylcyclohexane
n-type semiconductor [6,6]-phenyl-C61-butyric acid methyl (MCH), cyclohexane, n-hexane, n-heptane) and in tetra-
ester (PCBM).
chloroethylene the CGC values are even less than 0.1 wt %.
Organogelators with such low CGC values are classified as
supergelators [4], and thus the present quaterthiophene gelator
T1 belongs to this category. The ability of T1 to gelate such a
Results and Discussions
Synthesis
The synthetic route to the newly designed quaterthiophene wide range of solvents and its significantly low CGC values can
derivative T1 is depicted in Scheme 2. Compounds 4 [22] and 5 be attributed to the favourable balance between the self-
Scheme 1: Structure of the quarterthiophene derivative T1.
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Beilstein J. Org. Chem. 2010, 6, 1070–1078.
Scheme 2: Synthetic route to T1. Reagent and conditions: a) Boc anhydride, CH2Cl2, 6 h, 0 °C–rt, 97%; b) NBS, DMF, rt, 12 h, 89%; c) TFA, CH2Cl2,
rt, 4 h, 99%; d) Et3N, CH2Cl2, 0 °C–rt, 78%; e) BuLi, THF, 0 °C, 1 h; f) Bu3SnCl, rt, 12 h; g) Pd(PPh3)2Cl2, DMF, 80 °C, 8 h, 82%.
Table 1: Gelation studies of T1 in various solvents.
Entry
Solvent
Observation
CGC (moles/lit.)
CGC (Wt %)
1
Toluene
G
1 × 10−3
1 × 10−3
2 × 10−4
4 × 10−4
3.75 × 10−4
0.4 × 10−3
_
0.20
0.19
0.04
0.08
0.09
0.10
_
2
Benzene
G
3
Methylcyclohexane
Cyclohexane
n-Heptane
n-Hexane
G
4
G
5
G
6
G
7
CHCl3
soluble
8
CH2Cl2
soluble
_
_
9
Chlorobenzene
Tetrachloroethylene
1,2-Dichloroethylene
1,4-Dioxan
THF
G
0.33 × 10−2
9.09 × 10−4
1.25 × 10−3
0.125 × 10−2
_
0.51
0.09
0.17
0.26
_
10
11
12
13
14
15
16
17
18
19
20
G
G
Ga
soluble
Dibutylether
Acetone
G
1 × 10−3
1.11 × 10−3
0.5 × 10−3
_
0.22
0.24
0.12
_
Ga
Triethylamine
Acetonitrile
DMF
G
not soluble
G
1 × 10−3
_
0.18
_
DMSO
gel-like ppt.
Ga
Ethanol
1 × 10−3
0.21
aOpaque gel.
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Self-assembly studies by UV-vis spec-
troscopy
assembly propensity of the gelator and good solubility due to
the presence of the trialkoxybenzamide groups.
Self-assembly of T1 in solution was examined by UV-vis spec-
AFM investigations
troscopy. Chloroform is known to be an excellent solvent for
The topology of gels of quaterthiophene derivative T1 was the study of rigid π-systems [20,21], and the oligothiophene
examined by atomic force microscopy (AFM) in the tapping chromophore T1 has good solubility in this solvent. However,
mode. As an illustrative example, the AFM images of T1 gel in as noted above, in nonpolar solvents such as n-heptane, gela-
MCH deposited on highly ordered pyrolytic graphite (HOPG) tion was observed at extremely low CGC values. Thus, we
are shown in Figure 1. These images clearly show intercon- compared the UV-vis spectra of T1 in chloroform and
nected long fibers a few micrometers in length and bundles that n-heptane at 0.05 mM concentration (Figure 2a).
are responsible for the gelation of the solvents. At nanometer to
micrometer resolution, a fibrous network is observed that In chloroform the π-π* transition band appeared at 400 nm,
contains smaller fibers (indicated by yellow arrows in whilst in n-heptane it was shifted significantly to a lower wave-
Figure 1C) with a mean height of 2.3±0.3 nm and width of length (374 nm). In n-heptane, additional shoulders appeared at
7.0±1.0 nm.
420, 461 and 513 nm that were absent in the spectrum recorded
Figure 1: AFM height images of a film spin-coated from diluted gel solution of T1 in MCH (2 × 10−3 M) onto HOPG (A, B and C). The z scale (90, 60
and 25 nm, respectively) is shown under the respective image. Inset in 1A: a photograph of gel in cyclohexane at 1.5 mM concentration.
Figure 2: a) UV-vis spectra of T1 in chloroform (dashed line) and n-heptane (solid line); b) UV-vis spectra of T1 in n-heptane at different tempera-
tures. Concentration of T1 is 5 x 10−5 M.
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Beilstein J. Org. Chem. 2010, 6, 1070–1078.
in chloroform. These results are in accord with the literature
reports for the formation of H-aggregates of oligothiophenes
[19] and can be attributed to an excitonic interaction as well as
an increase in the conformational order in the assembled state
[23]. To test the reversibility of the self-assembly process, vari-
able temperature UV-vis experiments were performed in
n-heptane. These clearly showed that when the temperature was
gradually raised from 45 °C to 85 °C, the spectral pattern
changed significantly (Figure 2b). The λmax value shifted from
374 nm to 400 nm and the shoulders at higher wavelengths
(420, 461 and 513 nm) gradually disappeared. At the higher
temperature, the spectrum resembles quite well that observed in
chloroform solution (Figure 2a). These results suggest disas-
sembly of the H-type aggregate to monomeric building blocks
at elevated temperature. The self-assembly of T1 at such low
concentrations can be attributed to the synergistic effect of π-π-
stacking among the oligothiophene chromophores and intermo-
lecular hydrogen bonding between the amide groups of the
neighbouring chromophores (Scheme 3). To ascertain the
involvement of hydrogen bonding in the self-assembly, we
examined the effect of a protic solvent, e.g. MeOH, on the self-
assembly process by UV-vis spectroscopy. MeOH itself can be
involved in H-bonding interaction with the amide groups, and
thus expected to interfere with the inter-chromophoric
hydrogen-bonding interaction and to disrupt the assembly. Note
that, as methanol is not miscible with n-heptane, cyclohexane
was used as nonpolar solvent for this experiment. It can be seen
in Figure 3 that in the presence of 2.4% MeOH the absorption
spectrum of T1 in cyclohexane changed significantly. The
shoulders at longer wavelength disappeared and the λmax value
shifted from 382 nm to 399 nm, suggesting disassembly of the
aggregate into monomers. Thus, it is evident that hydrogen
bonding is essential for the self-assembly of T1, particularly at
such a low concentration of 5 x 10−5 M.
Scheme 3: Proposed mode of self-assembly of T1.
Studies on blends of T1 with PCBM
Figure 3: UV-vis spectra of T1 (concentration 5 x 10−5 M) in cyclo-
hexane (solid line) and 2.4% MeOH in cyclohexane (dashed line) at
25 °C.
The fullerene derivative [6,6]-phenyl-C61-butyric acid methyl
ester (PCBM) is a well-known n-type semiconductor and its
blends with various electron-donor materials have been exten-
sively used in solar cell devices [24]. The morphology of the related to PCBM aggregates. The height and width of the long
blend of donor and acceptor materials plays a prominent role in fibers were estimated to be 2.4±0.3 nm and 6.0±01.0 nm, res-
device performance [25]. Recently, we reported that a n-type pectively, which very closely match with the values observed
perylene bisimide organogelator exhibits photovoltaic activity for the self-assembly of T1 alone (Figure 1). This indicates that
with a p-type semiconducting polymer [26]. In this work, as an PCBM does not interfere in the self-assembly of T1.
initial study we characterized the morphology of a mixture of
PCBM with the p-type semiconducting oligothiophene-based Determination of charge carrier mobility
gelator T1 to elucidate the prospect of this system being used as It was anticipated that the well-organized π-stacked assembly of
a photovoltaic material. Figure 4 depicts the AFM images of a oligothiophene chromophores would provide percolation path-
mixture of T1 and PCBM on HOPG in which two types of ways for charge transport, similar to the previously reported
aggregates are visible. The observed long fibers can be attrib- results for mono- and bithiophene bisurea compunds [18].
uted to aggregates of T1 and the spherical nano-objects can be Therefore, the charge transport properties of T1 in the solid
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Beilstein J. Org. Chem. 2010, 6, 1070–1078.
Figure 4: AFM height images (A and B) of a film spin-coated from MCH solution (concentration 5 x 10−4 M) of a 1:1 mixture of T1 and PCBM onto
HOPG. The z scale (9 nm and 8 nm, respectively) is shown under the respective image. Figure 4C depicts cross-section analysis along the yellow line
1-1' in image B.
state were investigated by pulse radiolysis time resolved The lower limits of Σμmin (the sum of the mobilities of the posi-
microwave conductivity (PR-TRMC) measurements [27]. tive and negative charge carriers) were estimated from the rela-
tion Σμmin = Ep(Δσ/D), where Ep is the average electron-hole
PR-TRMC measurements were performed with a solid pair formation energy [28]. The mobility values obtained in this
(powder) sample of T1 using the same methodology as reported way at various temperatures are listed in Table 2. The charge
previously [27,28]. The sample (~32.5 mg) was irradiated with carrier mobility of T1 at 20 °C was found to be 2.9 × 10−3 cm2
a short pulse of 3 MeV electrons, which lead to the formation of V−1 s−1. When the sample was heated up to 110 °C, no signifi-
charges in the material during the pulse. The conductivity was cant difference was observed in the mobility value compared to
measured as a function of time by microwave conductivity that at 20 °C, indicating good thermal stability of the supra-
measurements. The dose-normalized PR-TRMC transients for molecular assembly of T1. A repeat measurement of mobility at
different irradiation doses at a temperature of 20 ºC are shown 20 °C after the sample was annealed revealed a slightly higher
in Figure 5. The decay is the same for all irradiation doses, value (4.2 × 10−3 cm2 V−1 s−1), indicating an improvement of
which indicates first order decay of the charge carriers. Such the supramolecular order in the material on annealing. It is
first order decay is typically observed for columnar materials interesting to note that the mobility value obtained for T1 is
and can be due to either trapping of charges or geminate recom- very close to that reported for non-regio regular alkyl-substi-
bination of electrons and holes [28].
tuted polythiophenes (Σμmin = 7 × 10−3 cm2 V−1 s−1) [29],
suggesting similar electronic coupling between oligothiophenes
in the gelated π-stacks.
Table 2: Charge carrier mobilities of T1 at various temperatures in the
sequence as measured in two experimental series.
T (°C)
Σμmin
T (°C)
Σμmin
(cm2 V−1 s−1)
(cm2 V−1 s−1)
20
0
0.0030
0.0032
0.0031
0.0030
0.0030
0.0032
0.0029
0.0028
0.0026
80
100
110
100
80
0.0024
0.0021
0.0024
0.0027
0.0031
0.0034
0.0039
0.0042
−20
−40
−20
0
60
20
40
60
40
20
Figure 5: Variation of dose-normalized conductivity transients (Δσ/D)
with time for T1.
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Beilstein J. Org. Chem. 2010, 6, 1070–1078.
Conclusion
Atomic force microscopy (AFM) measurements. AFM
We have demonstrated the self-assembly and charge transport measurements were carried out under ambient conditions with a
properties of a trialkoxybenzamide-functionalized quaterthio- Veeco MultiModeTM Nanoscope IV system operating in the
phene π-system. Our studies revealed the versatile and very tapping mode in air. Silicon cantilevers (Olympus Corporation,
effective gelation ability of the present system compared to the Japan) with a resonance frequency of ~300 kHz and spring
previously reported oligothiophene gelators. The critical gela- constant of ~42 N/m were used. A solution of T1 in methylcy-
tion concentrations in numerous solvents are remarkably low clohexane (MCH) with a concentration of 2 × 10−3 M was spin-
and in few cases even in the range of supergelators. The impact coated onto highly oriented pyrolytic graphite (HOPG) at
of facile self-assembly of newly developed oligothiophene 6000 rpm. The sample of a T1-PCBM mixture was prepared by
building block on its material properties is reflected in spin-coating of MCH solution with a concentration of 5 ×
promising charge transport characteristics as revealed by 10−4 M onto HOPG at 4000 rpm. The height of the observed
PR-TRMC measurements. When compared with ordinary amor- fibers was determined by statistical analysis on the premise that
phous or crystalline organic semiconductors it should be taken the fibers lay on a thin film. Note that, due to the AFM tip
into account that the oligothiophene moiety, which is respon- broadening effect, the actual width of aggregates is usually
sible for charge transport, is only 19% of the total molecular smaller than the apparent one.
weight of T1 and the remainder being made up by long alkyl
chains that do not contribute to charge carrier mobility. AFM Pulse radiolysis time resolved microwave conductivity (PR-
studies revealed self-sorted assembly of p-type oligothiophene TRMC) measurements. Conductivity measurements of
gelator and n-type PCBM in their blend which might offer quaterthiophene T1 were performed on a solid (powder) sample
some prospect for photocurrent generation [30].
(about 32.5 mg) that was manually compressed into a perspex
container. The sample was placed in a microwave cell,
consisting of a piece of rectangular waveguide with inner
Experimental
Materials and methods. All reagents and solvents were dimensions of 3.55 × 7.00 mm2 and short circuited with a metal
purchased from commercial sources and purified by standard end plate. The materials were uniformly ionized with a
protocols [31]. Spectroscopic grade solvents were used as nanosecond pulse of 3 MeV electrons from a Van de Graaff
received for spectroscopic studies. 1H NMR spectra were accelerator. The energy absorbed by the sample is accurately
recorded on a 400 MHz Bruker NMR spectrometer with tetra- known from dosimetry and leads to the formation of a micro-
methylsilane (TMS) as the internal standard. UV-vis experi- molar concentration of charge carriers (ca. 10−21 m−3). The
ments were carried out on a Perkin-Elmer Lambda 40P spec- change in conductivity due to creation of these charges was
trometer equipped with a Peltier system for temperature control. measured by time resolved microwave conductivity (TRMC)
measurements [27].
Gelation tests. A measured amount of T1 and the appropriate
solvent were taken together in a sample vial, heated to dissolve Synthesis and characterization. 3,4,5-Tris(dodecyloxy)-
the sample and then left at room temperature. After 30 minutes, benzoyl chloride (5) and compounds 2, 3, 4 and 8 were
the gelation was tested by the “stable to inversion” method.
prepared according to literature reported procedures and charac-
terized by 1H NMR and UV-vis spectroscopy. New compounds
UV-vis spectroscopic studies. A stock solution of T1 was (6 and T1) were characterized by 1H NMR, UV-vis, HRMS
prepared in chloroform with 1 mM concentration. A measured (ESI) and elemental analysis.
amount of stock solution was transferred to another vial and the
solvent removed by blowing argon gas over it. To this vial, a Tert-butyl 2-(thiophen-2-yl)ethylcarbamate (2). To a solu-
measured amount of solvent such as n-heptane or cyclohexane tion of 2-(thiophen-2-yl) ethylamine (1.63 g, 0.013 mol) in
was added to give the desired concentration and the mixture 10 mL CHCl3, a solution of Boc-anhydride (2.8 g, 0.013 mol)
then gently heated in a warm water-bath to yield a homoge- in 10 mL CHCl3 was added dropwise and the reaction mixture
neous solution. The solutions were allowed to equilibrate at stirred under an inert atmosphere for 6 h at room temperature.
room temperature for 2 h before performing UV-vis experi- The volatiles were then removed at reduced pressure to yield
ments. For variable temperature studies, the temperature was the crude 2 as a colourless oil (97%). 1H NMR (400 MHz,
changed from lower to higher values and the sample equili- CDCl3, TMS, 300 K): δ (ppm) = 7.15 (d, 1H), 6.95–6.83 (m,
brated for 10 min prior to each measurement after the particular 1H), 6.83 (m, 1H), 4.65 (broad peak, 1H), 3.38 (t, J = 6.24 Hz,
temperature was reached.
2H), 3.01(t, J = 6.68 Hz, 2H), 1.44 (s, 9H); UV-vis (CH2Cl2):
λmax (ε) = 235 nm (0.697 × 104 M−1cm−1).
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Beilstein J. Org. Chem. 2010, 6, 1070–1078.
Tert-butyl 2-(5-bromothiophen-2-yl)ethylcarbamate (3). To Quaterthiophene gelator T1. n-BuLi (360 μL in 2 mL dry
an ice-cold solution of compound 2 (0.77 g, 3.38 mmol) in THF) was added to a round-bottomed flask, flushed with argon
10 mL DMF, a solution of NBS (0.603 g, 3.38 mmol) in 5 mL gas for 15 minutes, and then cooled to 0 °C in an ice-bath. To
DMF was added dropwise. After the addition was complete, the this solution, a solution of 2, 2´-bithiophene in dry THF
reaction mixture was stirred at room temperature for a further (68.0 mg in 5 mL) was added dropwise under continuous flow
12 h, then poured into 100 mL water and extracted with (2 × 30) of argon. A white solid precipitate was formed. The reaction
mL diethylether. The combined organic layer was dried over mixture was stirred at room temperature for 1 h and then
anhydrous Na2SO4 and solvent removed to give the crude pro- immersed in an ice-bath. To this cold solution, 400 μL Bu3SnCl
duct as a light brown oil (90%) which was used in the next step was added which caused the precipitate to dissolve immedi-
without further purification. 1H NMR (400 MHz, CDCl3, TMS, ately. The reaction mixture was stirred at room for further 12 h
300 K): δ (ppm) = 6.88 (d, J = 3.64 Hz, 1H), 6.59 (d, J = 3.72 under an argon atmosphere. The volatiles were removed under
Hz, 1H), 4.63 (broad peak, 1H), 3.35 (t, J = 5.44 Hz, 2H), 2.93 reduced pressure to give the crude product as a white pasty
(t, J = 6.60 Hz, 2H), 1.44 (s, 9H); UV-vis (CH2Cl2): λmax (ε) = mass. The crude product was dissolved in 20 mL dry DMF,
238 nm (0.735 × 104 M−1cm−1).
compound 9 added and the flask evacuated, purged three times
with argon and ~15 mg of the Pd-catalyst added under contin-
2-(5-Bromothiophen-2-yl)ethylamine (4). To a solution of uous flow of argon. The reaction mixture was then heated at
tert-butyl 2-(5-bromothiophene-2-yl)ethylcarbamate (3) in 80 °C for 8 h under an argon atmosphere. It was observed that
5 mL CH2Cl2, 5 mL TFA was added and the reaction mixture an orange precipitate appeared within first 30 min, which
stirred at rt under an argon atmosphere for 2 h. The volatiles almost dissolved as the reaction progressed. After 8 h the reac-
were then removed under reduced pressure to afford the crude tion was stopped, cooled to rt and poured into 200 mL MeOH.
product as a light brown oil (96%) which was used in the next A yellowish orange precipitate was separated by filtration and
step without further purification. 1H NMR (400 MHz, CDCl3, dried in vacuum to give the crude product as a yellow solid. The
TMS, 300 K): δ (ppm) = 7.48 (broad s, 2H); 6.90 (d, J = 3.72 crude product was purified by column chromatography on silica
Hz, 1H), 6.67 (d, J = 3.64 Hz, 1H), 3.28 (m, 2H), 3.15 (t, J = gel with 2% methanol in chloroform as eluent to afford the pure
7.04 Hz, 2H); UV-vis (CH2Cl2): λmax (ε) = 238 nm (0.741 × product as a yellow solid (78%). M.p. 144 °C. 1H NMR (400
104 M−1cm−1).
MHz, CDCl3, TMS, 300 K): δ (ppm) = 7.04–7.00 (m, 6H), 6.79
(s, 4H), 6.18 (s, 2H), 6.78–6.75 (m, 2H), 3.99–3.95 (m, 12H),
N-2-(5-Bromothiophen-2-yl)ethyl) 3,4,5-tris(dodecyloxy)- 3.73–3.69 (m, 4H), 3.14–3.10 (m, 4H),1.81–1.25 (m, 120H),
benzamide (6). Compound 4 (2.94 mmol) was dissolved in 0.89–0.85 (m, 18H); UV-vis (CH2Cl2): λmax (ε) = 262 nm (1.76
5 mL dry CH2Cl2 and cooled in an ice-bath. To this cold solu- × 104 M−1 cm−1), 405 nm (2.90 × 104 M−1 cm−1); HRMS
tion, 4 mL triethylamine was added slowly. The resulting mix- (ESI): m/z calcd for C106H172N2Na1O8S4 [M + Na]+
ture was ice-cooled for an additional 10 minutes and then a :1752.1881; found: 1752.1920; MS (MALDI) m/z calcd for
solution of compound 5 in 10 mL dry CH2Cl2 was added drop- C106H172N2O8S4 [M + H]+ 1730.206, found: 1730.265;
wise. The reaction mixture was stirred at rt for 12 h, diluted elemental analysis: calcd for C106H172N2Na1O8S4: C, 73.56, H,
with a further 25 mL CH2Cl2 and washed successively with 10.02, N, 1.62, found: C, 73.32, H, 9.81, N, 1.73.
water (2 × 50 mL), dil. HCl (2 × 50 mL) and finally with 50 mL
brine. The combined organic layer was dried over anhydrous Acknowledgement
Na2SO4 and solvent removed under reduced pressure to give SG thanks the Alexander von Humboldt foundation for a post-
the crude product as a light yellow solid which was purified by doctoral fellowship.
column chromatography on silica gel with CH2Cl2 as eluent.
References
1. Lehn, J.-M. Supramolecular Chemistry - Concepts and Perspectives;
The product was further purified by dissolving it in 5 mL
CH2Cl2 and re-precipitating from 200 mL n-hexane to yield a
Wiley-VCH: Weinheim, 1995.
white solid (67%). M.p. 76–78 °C; 1H NMR (400 MHz, CDCl3,
2. Hoeben, F. M.; Jonkheijm, P.; Meijer, E. W.; Schenning, A. P. H. J.
TMS, 300 K): δ (ppm) = 6.91–6.90 (m, 3H), 6.64 (d, J = 3.64
Chem. Rev. 2005, 105, 1491–1546. doi:10.1021/cr030070z
Hz, 1H), 6.13 (broad s, 1H), 4.00–3.96 (m, 6H), 3.69–3.63 (m,
3. Fages, F. Low Molecular Mass Gelators; Topics in Current Chemistry,
2H), 3.07 (t, J = 6.44 Hz, 2H), 1.76–1.48 (m, 60H), 0.88 (t, J =
7.00 Hz, 9H); UV-vis (CH2Cl2): λmax (ε) = 257 nm (1.381 ×
104 M−1 cm−1), 290 nm (0.296 × 104 M−1 cm−1); HRMS (ESI):
m/z calcd for C49H85BrNO4S [M + 2H]+: 862.5372; found:
862.5377; elemental analysis: calcd for C49H85BrNO4S: C,
68.18, H, 9.81, N, 1.62, found: C, 67.93, H, 9.70, N, 1.76.
Vol. 256; Springer: Berlin, Germany, 2005. doi:10.1007/b105250
4. Bouas-Laurent, H.; Desvergne, J.-P. In Molecular Gels: Materials with
Self-Assembled Fibrilla Networks; Weiss, G. R.; Terech, P., Eds.;
Chapter 12; Springer: Netherlands, 2006.
5. Ajayaghosh, A.; Praveen, V. K. Acc. Chem. Res. 2007, 40, 644–665.
doi:10.1021/ar7000364
1077

Beilstein J. Org. Chem. 2010, 6, 1070–1078.
6. Prasanthkumar, S.; Saeki, A.; Seki, S.; Ajayaghosh, A.
J. Am. Chem. Soc. 2010, 132, 8866–8867. doi:10.1021/ja103685j
7. Ajayaghosh, A.; Varghese, R.; Mahesh, S.; Praveen, V. K.
Angew. Chem., Int. Ed. 2006, 45, 7729–7732.
30.Yamamoto, Y.; Fukushima, T.; Suna, Y.; Ishii, N.; Saeki, A.; Seki, S.;
Tagawa, S.; Taniguchi, M.; Kawai, T.; Aida, T. Science 2006, 314,
1761–1764. doi:10.1126/science.1134441
31.Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of
Laboratory chemicals, 2nd ed.; Pergamon: Oxford, 1980.
doi:10.1002/anie.200603238
8. Engelkamp, H.; Middelbeek, S.; Nolte, R. J. M. Science 1999, 284,
785–790. doi:10.1126/science.284.5415.785
9. Malik, S.; Kawano, S-i.; Fujita, N.; Shinkai, S. Tetrahedron 2007, 63,
7326–7333. doi:10.1016/j.tet.2007.05.027
License and Terms
10.Sugiyasu, K.; Fujita, N.; Shinkai, S. Angew. Chem., Int. Ed. 2004, 43,
1229–1233. doi:10.1002/anie.200352458
This is an Open Access article under the terms of the
Creative Commons Attribution License
11.Mukhopadhyay, P.; Iwashita, Y.; Shirakawa, M.; Kawano, S-i.;
Fujita, N.; Shinkai, S. Angew. Chem., Int. Ed. 2006, 45, 1592–1595.
doi:10.1002/anie.200503158
(http://creativecommons.org/licenses/by/2.0), which
permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
12.Li, X.-Q.; Stepanenko, V.; Chen, Z.; Prins, P.; Siebbeles, L. D. A.;
Würthner, F. Chem. Commun. 2006, 3871–3873.
doi:10.1039/b611422a
13.Del Guerzo, A.; Olive, A. G. L.; Reichwagen, J.; Hopf, H.;
Desvergne, J.-P. J. Am. Chem. Soc. 2005, 127, 17984–17985.
doi:10.1021/ja0566228
The license is subject to the Beilstein Journal of Organic
Chemistry terms and conditions:
(http://www.beilstein-journals.org/bjoc)
14.Desvergne, J. P.; Olive, A. G. L.; Sangeetha, N. M.; Reichwagen, J.;
Hopf, H.; Del Guerzo, A. Pure Appl. Chem. 2006, 78, 2333–2339.
doi:10.1351/pac200678122333
The definitive version of this article is the electronic one
which can be found at:
15.Yagai, S.; Ishii, M.; Karatsu, T.; Kitamura, A. Angew. Chem., Int. Ed.
2007, 46, 8005–8009. doi:10.1002/anie.200702263
16.Yao, S.; Beginn, U.; Greß, T.; Lysetska, M.; Würthner, F.
J. Am. Chem. Soc. 2004, 126, 8336–8348. doi:10.1021/ja0496367
17.Mishra, A.; Ma, C.-Q.; Bäuerle, P. Chem. Rev. 2009, 109, 1141–1276.
doi:10.1021/cr8004229
doi:10.3762/bjoc.6.122
18.Schoonbeek, F. S.; Van Esch, J. H.; Wegewijs, B.; Rep, D. B. A.;
De Haas, M. P.; Klapwijk, T. M.; Kellogg, R. M.; Feringa, B. L.
Angew. Chem., Int. Ed. 1999, 38, 1393–1397.
doi:10.1002/(SICI)1521-3773(19990517)38:10<1393::AID-ANIE1393>3
.0.CO;2-H
19.Kawano, S.; Fujita, N.; Shinkai, S. Chem.–Eur. J. 2005, 11,
4735–4742. doi:10.1002/chem.200500274
20.Ghosh, S.; Li, X.-Q.; Stepanenko, V.; Würthner, F. Chem.–Eur. J. 2008,
14, 11343–11357. doi:10.1002/chem.200801454
21.Würthner, F.; Bauer, C.; Stepanenko, V.; Yagai, S. Adv. Mater. 2008,
20, 1695–1698. doi:10.1002/adma.200702935
22.Venkatachalam, T. K.; Sudbeck, E. A.; Uckun, F. M. Tetrahedron Lett.
2001, 42, 6629–6632. doi:10.1016/s0040-4039(01)01290-4
23.Langeveld-Voss, B. M. W.; Waterval, R. J. M.; Janssen, R. A. J.;
Meijer, E. W. Macromolecules 1999, 32, 227–230.
doi:10.1021/ma981349y
24.Nelson, J. Curr. Opin. Solid State Mater. Sci. 2002, 6, 87–95.
doi:10.1016/s1359-0286(02)00006-2
25.Van Duren, J. K. J.; Yang, X.; Loos, J.; Bulle-Lieuwma, C. W. T.;
Sieval, A. B.; Hummelen, J. C.; Janssen, R. A. J. Adv. Funct. Mater.
2004, 14, 425–434. doi:10.1002/adfm.200305049
26.Wicklein, A.; Ghosh, S.; Sommer, M.; Würthner, F.; Thelakkat, M.
ACS Nano 2009, 3, 1107–1114. doi:10.1021/nn9001165
27.Warman, J. M.; de Haas, M. P.; Dicker, G.; Grozema, F. C.; Piris, J.;
Debije, M. G. Chem. Mater. 2004, 16, 4600–4609.
doi:10.1021/cm049577w
28.Warman, J. M.; Van de Craats, A. M. Mol. Cryst. Liq. Cryst. 2003, 396,
41–72. doi:10.1080/15421400390213186
29.Van der Laan, G. P.; Haas, M. P. D.; Buik, A.; De Ruiter, B. Synth. Met.
1993, 55, 4930–4935. doi:10.1016/0379-6779(93)90841-J
1078