Two-dimensional nanostructures by the assembly of n-type tetraazaanthracene-based conjugated molecules

Article abstract of DOI:10.1002/cphc.201300444

On the basis of our previous communication concerning a new family of thiophene-armed tetraazaanthracene molecules, we present a further intensive investigation on this class of compounds substituted with different alkyl chains and their self-assembled two-dimensional (2D) nanostructures. These tetraazaanthracene molecules with different alkyl chains were prepared in good yields using the synthetic strategy we developed. In addition to the expected typical n-type character, one compound exhibited aggregation behavior upon electrochemical reduction. Moreover, all molecules in the neutral state showed a strong tendency to aggregate in a binary solvent, as confirmed by optical spectral measurements. To investigate such self-assembly behavior, a phase-transfer method with a dichloromethane/methanol (2:3) binary solvent system was used to prepare the nanostructures. By means of atomic force microscopy, transmission electron microscopy, and X-ray diffraction, we found that the morphology of assembled 2D sheet-like structures could be adjusted by varying the alkyl chain. The weak interactions arising from the heteroatoms (N and S) in the conjugated backbones play a key role in the formation and stabilization of layered structures. Ruling chains: A set of n-type conjugated molecules containing a tetraazaanthracene core and different alkyl-chain arms is presented. In binary solvent mixtures, self-assembly into 2D sheet-like nanostructures takes place (see picture). By using different alkyl chains, morphology can be sensibly modified. The weak interactions arising from the heteroatoms in the conjugated backbones play a key role in the formation and stabilization of the layered structures.

Full text of DOI:10.1002/cphc.201300444

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Ruling chains: A set of n-type conjugat-
ed molecules containing a tetraazaan-
thracene core and different alkyl-chain
arms is presented. In binary solvent mix-
tures, self-assembly into 2D sheet-like
nanostructures takes place (see picture).
By using different alkyl chains, morphol-
ogy can be sensibly modified. The weak
interactions arising from the hetero-
atoms in the conjugated backbones
play a key role in the formation and sta-
bilization of the layered structures.
C. He, D. Wu, F. Zhang,* M. Xue,
X. Zhuang, F. Qiu, X. Feng*
&& – &&
Two-Dimensional Nanostructures by
the Assembly ofn-Type
Tetraazaanthracene-Based Conjugated
Molecules
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DOI: 10.1002/cphc.201300444
Two-Dimensional Nanostructures by the Assembly of
n-Type Tetraazaanthracene-Based Conjugated Molecules
Chunyang He,[a] Dongqing Wu,[a] Fan Zhang,*[a] Minzhao Xue,[a] Xiaodong Zhuang,[a]
Feng Qiu,[a] and Xinliang Feng*[a, b]
On the basis of our previous communication concerning a new
family of thiophene-armed tetraazaanthracene molecules, we
present a further intensive investigation on this class of com-
pounds substituted with different alkyl chains and their self-as-
sembled two-dimensional (2D) nanostructures. These tetra-
azaanthracene molecules with different alkyl chains were pre-
pared in good yields using the synthetic strategy we devel-
oped. In addition to the expected typical n-type character, one
compound exhibited aggregation behavior upon electrochemi-
cal reduction. Moreover, all molecules in the neutral state
showed a strong tendency to aggregate in a binary solvent, as
confirmed by optical spectral measurements. To investigate
such self-assembly behavior, a phase-transfer method with a di-
chloromethane/methanol (2:3) binary solvent system was used
to prepare the nanostructures. By means of atomic force mi-
croscopy, transmission electron microscopy, and X-ray diffrac-
tion, we found that the morphology of assembled 2D sheet-
like structures could be adjusted by varying the alkyl chain.
The weak interactions arising from the heteroatoms (N and S)
in the conjugated backbones play a key role in the formation
and stabilization of layered structures.
1. Introduction
In the last few years, two-dimensional (2D) materials have at-
tracted immense attention[1] because of their prominent fea-
tures such as high surface area, and structural flexibility, along
with potential applications in energy storage and conversion,
electronics, catalysis, and sensing.[2] Self-assembly of small mol-
ecules has provided an appealing strategy for the bottom-up
construction of free-standing 2D nanosheets.[3] Typically, these
long-range ordered nanostructures are stabilized by various
non-covalent intermolecular forces, such as hydrogen bonds,[5]
p-p,[4] ionic,[6] and charge-transfer interactions.[7] Regarding the
use of aromatic building blocks in self-assembly, the conjugat-
ed backbone cannot only provide p–p interactions to stabilize
the self-organized nanostructures, but also offers anisotropic
channels for the transportation of charge carriers.[8]
fore, it is highly desirable to develop n-type organic semicon-
ductors that can self-assemble into 2D nanostructures.
Recently, we developed an efficient synthesis of an H-
shaped 2,3,7,8-tetraazaanthracene with four thiophene arms,[12]
for which an electrochemical study revealed a typical n-type
character.[12] The embedded heteroatoms (N and S) in the con-
jugated backbone imparted not only donor–acceptor (D–A)
charge-transfer features, but also different intermolecular non-
covalent forces, such as N···S, S···S, and hydrogen bonds, which
have an important impact on their solid-state packing. In addi-
tion, the substituted alkyl chains at the periphery of the conju-
gated backbone can improve their solubility and influence the
molecular packing by means of cooperative van der Waals in-
teractions.[13]
Admittedly, n-type organic semiconductors show potential
applicability in organic thin-film field-effect transistors (OTFTs)[9]
and organic solar cells (OSCs).[10] However, the self-assembly of
n-type conjugated molecules has been less explored.[11] There-
Inspired by these findings, we designed and synthesized
a series of H-shaped molecules comprising a 2,3,7,8-tetraaza-
anthracene core and thiophene arms substituted with different
alkyl chains (Figure 1). Their unique self-assembled 2D nano-
structures, obtained by a phase-transfer method, were the
focus of attention. All the compounds have been fully charac-
1
terized by H and 13C nuclear magnetic resonance (NMR) and
[a] C. He, Prof. D. Wu, Prof. F. Zhang, Prof. M. Xue, Dr. X. Zhuang, Dr. F. Qiu,
Prof. X. Feng
high-resolution mass spectra (HRMS-ESI), showing full consis-
tency.
School of Chemistry and Chemical Engineering
Shanghai Jiao Tong University
800 Dongchuan Road, Shanghai 200240 (P.R. China)
E-mail: fan-zhang@sjtu.edu.cn
feng@mpip-mainz.mpg.de
[b] Prof. X. Feng
Max-Planck Institute for Polymer Research
Ackermannweg 10, 55128, Mainz (Germany)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cphc.201300444.
Figure 1. Chemical structures of 1–4.
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behavior of 2 in the reduced state.[14] Encouraged by such an
unexpected result, attempts to understand the effect of the
alkyl chain on the self-assembly behavior of 1–4 were carried
out.
The optical properties of compound 2 were investigated in
a series of binary solvent mixtures (dichloromethane/methanol)
to elucidate the self-assembly process. Upon addition of meth-
anol (<50% volume fractions) to the dichloromethane solution
of 2, the intensity of the main absorption bands in the UV/Vis
spectra is only slightly increased (Figure 3a). However, on in-
Scheme 1. Synthesis of target molecules 1–4.
2. Results and Discussion
Alkyl-modified p-conjunction compounds 1–4 (Scheme 1) were
synthesized from the key starting compound pyromellitoyl
chloride (5). In accord with our previously reported method,[12]
5 was prepared from 1,2,4,5-benzenetetracarboxylic anhydride
and phosphorus pentachloride at 1908C. Unfortunately, it was
not possible to obtain compound 7 directly by reaction of
thienyl Grignard reagents with 5. Therefore, the S-pyridinyl
moiety was adopted as an appropriate leaving group to substi-
tute the chloride group, by treating 5 with 2-mercaptopyridine
as the reactant, and triethylamine (TEA) as the catalyst at 08C
for 30 min. To avoid rearrangement, the reaction was worked
up by quick addition of dilute hydrochloric acid. The resulting
solid was recrystallized in dichloromethane/diethyl ether, to
yield compound 6 (Scheme 1) as pale-yellow crystals. After-
wards, freshly prepared 2-thienylmagnesium bromide was
added to the suspension of 6 in tetrahydrofuran (THF) at 08C,
affording 7a–d in yields from 31–34%. Finally, 7a–d were
treated with excess hydrazine hydrate, to build up the target
compounds 1–4 in good yields.
Figure 3. a) UV/Vis absorption and b) fluorescence emission spectra (10À5 m)
showing variations in intensity for a dichloromethane/methanol mixture
with different methanol fractions.
As typical examples of the prepared compounds, the elec-
trochemical behavior of 1 and 2 was studied by cyclic voltam-
metry (CV, Figure 2). The CV of 2 shows successive reversible
cathodic peaks, indicative of n-type character. Notably, a slight
splitting into an intense redox peak at À1.12 V and a shoulder
redox peak at around À0.91 V can be observed, in contrast
with the reduction redox process of 1, displaying only one
creasing the methanol content up to 50%, the intensity of the
main absorption maxima initially declines, and then becomes
broad with a leveling-off of long-wavelength tails at higher
methanol contents, which are typical characteristics of the for-
mation of nanometric aggregates.[15] In contrast, a dramatic
change in fluorescence is observed when methanol is added
to the dichloromethane solution of 2 (Figure 3b). Gradually in-
creasing the volume fraction of methanol from 0 to 30% sig-
nificantly enhances emission intensity, along with a redshift in
the emission band from 568 to 581 nm. The enhancement by
effect of the methanol fraction (up to 30%) leads to a signifi-
well-resolved peak at À0.89 V with
a hexyl substituted
group.[11] Such phenomenon is likely due to the aggregation
!
cant increase in emission intensity (Figure 3b, ), probably
due to a solvent effect. The emission is progressively quenched
upon further increase of the methanol fraction (40%, Fig-
^
ure 3b, ). This result suggests that the aggregation of 2 was
formed in a binary solvent system with dichloromethane/meth-
anol>3:2.[16]
Aggregate morphology was investigated by scanning elec-
tron microscopy (SEM). The declined solubility of formed ag-
gregates can lead to the formation of a suspension, which can
help preserving the integrity of the nanostructures, protecting
Figure 2. Cyclic voltammograms of a) 1[12] and b) 2 in dichloromethane (scan
rate: 100 mVsÀ1).
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Figure 5. a) AFM images of 2D aggregates formed by 2. b) Representation of
a possible ordered arrangement for the assembly of 2, illustrating that the
thickness is approximately equivalent to ten mono-layers.
Figure 4. SEM images of self-assembled 2D nanosheets of a) 1 and b) 2. TEM
images of self-assembled 2D nanosheets of c) 1 and d) 2.
them from deformation, as they
are being transferred to a solid
substrate.[6a] We conducted the
assembly of 1–4 from a binary
solvent system in an optimized
2:3 ratio of dichloromethane/
methanol. Typically, 2, 12, 24,
and 48 h were required for 1–4
to form pronounced aggregates,
respectively. As shown in Fig-
ure 4a,b, remarkable 2D sheet-
like nanostructures are found for
1 and 2. The sheets of 1 show
Figure 6. SEM images of aggregates from the suspensions of a) 3 and b) 4 (The samples were prepared by drop-
casting of the suspensions in dichloromethane/methanol onto the silicon substrate).
equilateral
rhombus-shaped
structures with a size of 10–
30 mm. Self-assembly of 2 leads
to similar nanosheets with size
in the range of 1–2 mm. Transmission electron microscopy
(TEM) images confirm the nanosheet morphologies for 1 and
2. As shown in Figure 4c, 1 comprises a 2D nanosheet with an
equilateral length and width of 20–30 mm, with multiple-layer
stacking. Notably, the size of 2D aggregates formed from 2 is
more dispersive, with the same length and width of 1 mm (Fig-
ure 4d). The well-dispersed 2D nanosheet of 2 was further in-
vestigated by atomic force microscopy (AFM, Figure 5a), from
which a thickness of ~29.3 nm was measured.
Interestingly, pending arms of long octadecyl (C18) chains
(Figure 6a) lead to disk-like nanosheets with a diameter of
~600 nm (3), which stand in contrast to those of 1 and 2. Note
that the edges of the 2D structures become darker on going
from 1 to 3, which is probably attributable to the different
rates of the self-assembly processes. Furthermore, we found
that 4, substituted with branched C6À2 alkyl chains, leads to
the rod-like assembled structures with a length from 200 mm
to 2 mm (Figure 6b). Tailoring the decorated alkyl chains for
compounds 1–4 is seemingly an efficient way to control the
self-assembly behavior in a binary co-solvent system.
To elucidate the structural influence of the supramolecular
arrangement and macroscopic morphology, powder X-ray dif-
fraction (XRD) was employed to analyze the aggregation be-
havior of 1–4. The diffraction pattern of 1 exhibits intense,
sharp peaks, indicating the high crystallinity of the assembled
2D nanosheets. Accordingly, the peaks at 2q=4.2, 8.4, and
16.98 in Figure 7a can be indexed as (100), (200), and (300) re-
flections, respectively, and are associated with a lamellar pack-
ing.[17] Compounds 2 and 3 also reveal three well-resolved dif-
fraction peaks in the range 2–108, with the formation of a la-
mellar structure (Figure 7b,c). The reflection peaks of 1–3 at
2q=20–218 are known to originate from the ordered packing
of alkyl chains. The strong peak at a small angle in 1 dwarfs
the peaks at 2q=20–218, a magnification of the region (Fig-
ure 7a) provides a better view. In addition, the reflection peaks
at 2q=23–258 can be attributed to the p–p stacking of aro-
matic segments.[17c] Notably, with the increase in alkyl-chain
length from 1 to 3, the intensity of the peaks at 20–218 be-
comes stronger, suggesting enhanced interaction of the alkyl
chains. In contrast to 1–3, the XRD pattern of 4 have a lower
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lar d spacing calculated from wide-angle X-ray diffraction
(2.04 nm) of 1 is exactly equal to the value derived from X-ray
single-crystal analysis,[12] implying the same molecular arrange-
ment in both, the 2D assemblies and the crystals. Based on the
structural analysis and the strong support for a long-range or-
dered assembly, a mechanism is proposed to explain the for-
mation of 2D nanostructures. As depicted in Figure 9, we can
Figure 7. X-ray diffraction patterns of 1–4 plotted against the angle 2q
(298 K).
intensity, along with less defined and broader peak shapes,
and deprived of the typical reflections related to lamellar fea-
tures (Figure 7d). In the small-angle region, sharp and clear re-
flections at 2q values of 4.2, 3.0, and 2.38 for 1–3, respectively,
are noted. As a consequence, the calculated XRD d spacings of
the (100) reflection value are 2.04, 2.94, and 3.87 nm, respec-
tively, on the basis of Bragg’s law. These results suggest that
the compounds with longer alkyl chains have a larger interlay-
er spacing in the aggregates.[6a]
Figure 9. Packing diagram and illustration of the 2D nanostructures forma-
tion for 1.
simulate the process of 2D formation on the basis of crystal
structure analysis of 1.[12] The analysis showed that four thio-
phene arms extend out of the rigid tetraazaanthracene plane
through free rotation around the CÀC bonds.[12] Such a non-
planar molecular conformation would allow multi-intermolecu-
lar interactions, including S···S interactions (0.385 nm), hydro-
gen bonding of N···H (0.292 nm), and C···H–p (0.340 nm) and
p–p interactions (0.333, 0.378 nm) (Figure S1 in the Supporting
Information), to create a synergistic effect for molecular self-as-
sembly along two axial directions, ultimately giving rise to
a single-layer nanosheet (route A). Subsequently, each single
sheet of assembled structures can undergo lamellar packing
by van der Waals interactions, resulting in a crystal structure
similar to those herein presented. The weak interaction from
the hydrogen bonding between nitrogen and hydrogen atoms
in neighboring molecules (0.292 nm) may also contribute to
the stability of the arrays, facilitating nanostructure formation
for 1–4. This is confirmed by Fourier transform infrared (FT-IR)
spectroscopy (Figure 10), in which the typical peaks located at
3446, 3434, 3445, and 3443 cmÀ1 for 1–4, respectively, can be
ascribed to the NÀH bond.[20] These weak interactions depend
solely on the relative location of each molecule, and serve as
the driving force for the simultaneous growth of the micro-
sheets along two axial directions, thus leading to the formation
of a rhomboid pattern with little differences in width and
length, rather than a ribbon-like or rectangular pattern.
Considering the thickness of the 2D nanostructures in 2 is
~29.3 nm and the calculated XRD d spacing of the (100) reflec-
tion value is 2.94 nm, a proposed molecular arrangement for 2
is shown in Figure 5b. The schematic representation indicates
that the 2D nanosheets of 2 are expected to consist of ten
layers. Note that the Dd value between 1 and 2 (0.90 nm) is
similar to that between 2 and 3 (0.93 nm). These values are
likely to derive from the double length of the hexyl chain moi-
eties, and are in line with values from earlier reports.[18] Hence,
the lamellar d spacing within the assemblies increases linearly
with the carbon number of the alkyl chains (Figure 8), from
which we can deduce the molecular arrangements in the as-
semblies of 1–3 should be the same.[19] Importantly, the lamel-
3. Conclusion
Figure 8. The linear relationship between the lamellar d spacing and the
carbon number of the alkyl chain reveals the same molecular arrangements
for compounds 1–3.
In summary, a series of n-type thiophene-armed tetraazaan-
thracene molecules with different peripheral alkyl chains were
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Materials
All reagents were obtained from commercial suppliers such as
Aladdin and J&K Chemical. All solvents were supplied by Sino-
pharm Chemical Reagent and used as received unless otherwise
noted. All air-sensitive reactions were carried out under a nitrogen
atmosphere and performed using Schlenk techniques. THF was
used freshly distilled from a suspension heated at reflux under ni-
trogen in the presence of sodium and benzophenone. Triethyl-
amine (TEA) was heated to reflux with calcium carbide prior to use.
Dichloromethane for fluorescence spectroscopy and UV/Vis spectra
studies were distilled from calcium hydride.
Synthesis of Precursors (5–7)
1,2,4,5-Benzenetetracarbonyl tetrachloride (5), 1,2,4,5-tetra(S-(pyri-
dine-2’-yl))benzenetetrathioate (6), and 1,2,4,5-tetra(5’-hexyl-thieno-
2’-yl)benzene (7a) were synthesized following published proce-
dures as described in our previous paper.[12]
Figure 10. FT-IR spectra of 1–4. The peaks at 3446, 3434, 3445, and
3443 cmÀ1 can be ascribed to the vibrational modes of the NÀH bond.
prepared. The electron-rich heteroatoms (N and S) in the mo-
lecular backbone play an important role in creating multiple
weak intermolecular interactions, inducing the formation of
layered structures in the solid-state packing. The self-assem-
blies of these molecules in a binary solvent system of dichloro-
methane/methanol reveal remarkable 2D nanosheet morpholo-
gies, which can be tuned by the modification of the peripheral
alkyl chains. This work offers a new approach to the creation
of uniform 2D organic nanomaterials, which may have poten-
tial applications in organic electronics.
Synthesis of 1,2,4,5-Tetra(5’-Dodecyl-Thieno-2’-yl)Benzene
(7b)
A solution of 2-bromo-5-dodecylthiophene (3.7 g, 11.18 mmol) in
THF (15 mL) was added drop wise to a mixture of iodine-activated
magnesium (0.29 g, 12.31 mmol) in THF (5 mL), and the mixture
was refluxed for 4 h at 508C under a nitrogen atmosphere to form
the Grignard reagent. Afterwards, the cold reagent was slowly
added to a flask containing 6 (1.0 g, 1.62 mmol) in dry THF (50 mL)
at 08C, and stirred overnight. Then, the reaction was quenched
with 10% HCl (100 mL), and extracted with ether. The combined
organic fractions were washed with 1m NaOH and water until
reaching neutral pH, then dried over Na2SO4, and the solvent was
removed under reduced pressure. After purification by recrystalliza-
tion from dichloromethane/diethyl ether, the product was ob-
tained as a white solid (0.63 g, 33.1%). 1H NMR (400 MHz, CDCl3)
d=7.98 (s, 1H), 7.36 (d, 3JH-H =4.0 Hz, 2H), 6.79 (d, 3JH-H =4.0 Hz,
2H), 2.82 (t, 3JH-H =7.6 Hz, 4H), 1.71–1.65 (m, 4H), 1.63–1.57 (m,
36H), 0.90–0.86 ppm (m, 6H); 13C NMR (100 MHz, CDCl3) d=
186.61, 158.68, 141.05, 140.92, 136.53, 129.71, 126.17, 32.15, 31.57,
31.03, 29.89, 22.93, 14.37 ppm; m.p. 166–1688C.
Experimental Section
General Method
1H and 13C NMR spectra were recorded on a Mercury Plus 400
(Varian, USA, 400 MHz for proton) spectrometer with tetramethylsi-
lane as the internal reference using CDCl3 as the solvent in all
cases. Mass spectra were recorded on a Bruker microTOF-Q-II
system. All yields given refer to isolated yields. UV/Vis spectra were
recorded on a HITACHI U-4100 spectrophotometer. The fluores-
cence spectroscopy emission spectra were obtained with a Fluoro-
Max-4 spectrophotometer. CV was performed on an Chenhua
650D electrochemical analyzer in distilled dichloromethane con-
taining recrystallized tetra-n-butyl-ammonium hexafluorophos-
phate (TBAPF6, 0.1m) as the supporting electrolyte at 298 K. XRD
measurements were carried out on a D/max-2200/PC (Rigaku
Corp., Japan) using Cu (40 kV, 30 mA) radiation. SEM measure-
ments were performed on an FEI Sirion-200 field emission scan-
ning electron microscope. The samples were prepared by drop-
casting the suspensions onto silicon wafers. TEM characterizations
were carried out on a JEM-2100 (JEOL Ltd., Japan) with an acceler-
ating voltage of 200 kV. The samples were prepared by drop-cast-
ing the suspensions onto copper grids covered with carbon film.
AFM studies were carried out on a Multimode Nanoscope (ID Ltd.,
USA) operated in tapping mode at room temperature. The samples
were prepared by drop-casting the suspensions onto silicon
wafers. X-ray crystallography was performed using a CAD4 DIFFAC-
TIS 586 diffractometer.
Synthesis of 1,2,4,5-Tetra(5’-Octodecyl-Thieno-2’-yl)Benzene
(7c)
A solution of 2-bromo-5-octodecylthiophene (3.0 g, 7.20 mmol) in
THF (10 mL) was slowly added to a mixture of iodine-activated
magnesium (0.21 g, 8.64 mmol) in THF (5 mL), to form the Grignard
reagent in 4 h. Afterwards, the cold reagent was slowly added to
a flask containing 6 (0.64 g, 1.01 mmol) in dry THF (50 mL) at 08C,
and stirred overnight. Then, the reaction was quenched with 10%
HCl (100 mL), and extracted with dichloromethane. The combined
organic fractions were washed with 1m NaOH and water until neu-
tral pH was measured, then dried over Na2SO4, and the solvent
was removed under reduced pressure. After purification by recrys-
tallization from dichloromethane/diethyl ether, the product was
1
obtained as a white solid (0.65 g, 39.3%). H NMR (400 MHz, CDCl3)
d=7.98 (s, 1H), 7.36 (d, 3JH-H =4.0 Hz, 2H), 6.79 (d, 3JH-H =4.0 Hz,
2H), 2.82 (t, 3JH-H =7.6 Hz, 4H), 1.71–1.67 (m, 4H), 1.65–1.20 (m,
60H), 0.90–0.86 ppm (m, 6H); 13C NMR (100 MHz, CDCl3) d=
186.59, 158.66, 141.03, 140.91, 136.51, 129.69, 126.15, 32.16, 31.58,
31.03, 29.94, 22.94, 14.37 ppm; m.p. 149–1518C.
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Synthesis of 1,2,4,5-Tetra(5’-(2’’-Ethylhexyl)-Thieno-2’-yl)-
Benzene (7d)
Synthesis of 1,4,6,9-Tetra(5-(2-Ethylhexyl)-Thien-2-yl)-2,3,7,8-
Tetrazaanthracene (4)
A
solution of 2-bromo-5-(2-ethylhexyl)thiophene (0.65 g,
A suspension of hydrazine hydrate (35.8 mg, 0.715 mmol) and 7d
(85.8 mg, 0.089 mmol) in ethanol (30 mL) was stirred for 2 days at
room temperature. The solvent was removed under reduced pres-
sure. After purification by column chromatography with CH2Cl2/pe-
troleum ether, the product was obtained as a red solid (68 mg,
2.36 mmol) in THF (3 mL) was slowly added to a mixture of iodine-
activated magnesium (63 mg, 2.83 mmol) in THF (2 mL), to form
the Grignard reagent in 4 h. Afterwards, the cold reagent was
slowly added to a flask containing 6 (211 mg, 0.337 mmol) in dry
THF (50 mL) at 08C, and stirred overnight. Then, the reaction was
quenched with 10% HCl (100 mL), and extracted with ether. The
combined organic fractions were washed with 1m NaOH and
water until reaching neutral pH, then dried over Na2SO4, and the
solvent was removed under reduced pressure. After purification by
column chromatography with CH2Cl2/petroleum ether as the
1
3
80.3%). H NMR (400 MHz, CDCl3) d=9.84 (s, 1H, Ph), 7.71 (d, JH-
3
3
H =3.8 Hz, 2H, Th-H-3), 6.99 (d, JH-H =3.8, 2H, Th-CH-4), 2.89 (d, JH-
H =6.7 Hz, 4H, CH2), 1.75–1.69 (m, 6H, CH2), 1.44–1.32 (m, 12H,
CH2), 0.89–0.85 ppm (m, 12H, CH3); 13C NMR (100 MHz, CDCl3) d=
152.24, 150.60, 136.41, 130.57, 126.68, 126.31, 125.69, 41.75,34.58,
32.71, 29.14, 25.86, 23.26, 14.37, 11.09 ppm; HRMS-ESI: m/z calcu-
lated for C58H78N4S4 [M+H] 958.5188, found, 959.5200; m.p. 143–
1458C.
eluent, the product was obtained as a pale yellow solid (110 mg,
34.1%). 1H NMR (400 MHz, CDCl3) d=8.00 (s, 1H), 7.35 (d, JH-H
3
=
4.0 Hz, 2H), 6.77 (d, 3JH-H =4.0 Hz, 2H), 2.76 (d, 3JH-H =6.8 Hz, 4H),
1.60–1.57 (m, 6H), 1.34–1.28 (m, 12H), 0.89–0.86 ppm (m, 12H);
13C NMR (100 MHz, CDCl3) d=186.54, 157.40, 148.18, 141.05,
136.42, 129.71, 127.10, 41.67, 34.99, 32.57, 29.01, 25.69, 23.16,
14.32, 10.97 ppm; m.p. 99–1018C.
Preparation of the Self-assembly Systems by Phase Transfer
(PT) Method
Methanol can increase the polarity of a solvent system and induce
better phase separation for amphiphilic molecules,[6a,21] so we used
a PT method with a dichloromethane/methanol binary solvent
system to investigate the self-assembly of 1–4.
Synthesis of 1,4,6,9-Tetra(5-Hexyl-Thien-2-yl)-2,3,7,8-Tetra-
azaanthracene (1)
Self-Assembly of 1–4
1,4,6,9-Tetra(5-hexyl-thien-2-yl)-2,3,7,8-tetraazaanthracene was syn-
thesized following published procedures as described in our previ-
ous paper.[12]
Compound 1: A homogeneous solution of 1 was prepared in
CH2Cl2 (4 mL, ~1 mm) at room temperature in a clean 20 mL
sample vial. Methanol (6 mL, poor solvent) was slowly added to
the solution so that two phases could be maintained. The biphasic
mixture was left undisturbed to induce assembly, which finally re-
sulted in a yellow suspension. The procedure for 2–4 was the
same, using instead ~0.5 mm concentrations of each correspond-
ing compound.
Synthesis of 1,4,6,9-Tetra(5-Dodecyl-Thien-2-yl)-2,3,7,8-Tetra-
azaanthracene (2)
A suspension of hydrazine hydrate (0.17 g, 3.36 mmol) and 7b
(0.5 g, 0.42 mmol) in ethanol (50 mL) was stirred for 2 days at
room temperature. After removing the solvent under reduced pres-
sure, the product was obtained as a yellow solid (0.45 g, 90.5%).
Acknowledgements
3
1H NMR (400 MHz, CDCl3) d=9.85 (s, 1H, Ph), 7.71(d, JH-H=3.7 Hz,
3
3
2H, Th-H-3), 6.97 (d, JH-H =3.7, 2H, Th-CH-4), 2.89 (d, JH-H =6.8 Hz,
4H, CH2), 1.75–1.69 (m, 4H, CH2), 1.77–1.27 (m, 36H, CH2), 0.90–
0.85 ppm (m, 6H, CH3); 13C NMR (100 MHz, CDCl3) d=152.32,
151.00, 136.07, 130.68, 126.40, 125.70, 32.16, 31.92, 30.69, 29.93,
29.85, 29.69, 29.60, 29.49, 22.93, 14.37 ppm; HRMS-ESI: m/z calcu-
lated for C74H110N4S4 [M+Na] 1205.7511, found, 1205.7529; m.
p. 153–1558C.
We acknowledge funding support from the Natural Science Foun-
dation of China (NSFC. 21174083), the Shanghai Committee of
Science and Technology (11JC1405400), the Shanghai Pujiang
Program (12J1405300), and the Shanghai Jiao Tong University
(211 Project). The authors thank Mr. Chong Cheng and Mr. Yi
Zhang for taking AFM of compound 2.
Keywords: nanostructures · noncovalent interactions · self-
assembly · tetraazaanthracene · two-dimensional structures
Synthesis of 1,4,6,9-Tetra(5-Octodecyl-Thien-2-yl)-2,3,7,8
Tetraazaanthracene (3)
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A suspension of hydrazine hydrate (0.052 g, 1.05 mmol) and 7c
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1
the product was obtained as a yellow solid (0.17 g, 86.3%). H NMR
3
(400 MHz, CDCl3) d=9.84 (s, 1H, Ph), 7.71 (d, JH-H =3.8 Hz, 2H, Th-
H-3), 6.99 (d, 3JH-H =3.8, 2H, Th-CH-4), 2.95 (t, 3JH-H =7.6 Hz, 4H,
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ESI: m/z calculated for C98H158N4S4 [M+H] 1520.1448; found,
1520.1515; m.p. 124–1268C.
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Received: May 6, 2013
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