Supramolecular gel-assisted formation of fullerene nanorods

Article abstract of DOI:10.1002/chem.201202721

Gel it like it is: Fullerene nanorods (see figure) with a length of several micrometers, can be easily synthesized by a supramolecular gel-assisted self-assembly method (SGAS). The results presented here may be useful for the design and construction of new organic nanomaterials by SGAS. Copyright

Full text of DOI:10.1002/chem.201202721

DOI: 10.1002/chem.201202721
Supramolecular Gel-Assisted Formation of Fullerene Nanorods
Chun Zhang,* Jing Wang, Jing-Jing Wang, Min Li, Xiang-Liang Yang, and Hui-Bi Xu[a]
Fullerene (C60), a truncated icosahedron with 20 hexagons
and 12 pentagons with a diameter of 7.1 ꢀ, has attracted
considerable attention because of its tremendous potential
in material science as a promising building block with
unique physical and chemical properties.[1,2] During the past
decade, construction of fullerene-based nanomaterials has
been called for because they are of great importance in the
development of optoelectronic and nanoelectronic devices.
There is currently an intensive effort to develop methods for
Figure 1. Chemical structures of gelators 1 and 2.
controlling the morphology of fullerene-based nanomateri-
als with low-dimensionality structures. So far, different
methods have been developed to control the morphology of
one-dimensional fullerene-based nanomaterials, including
crystal/precipitation,[3–6] template synthesis[7–9] and amphi-
philic assembly.[10–12] Although different fullerene nanomate-
rials, such as nanowhiskers,[13,14] nanowires,[4,12] nano-
tubes,[7,15,16] and nanorods[17–19] have been prepared with
these methods, developing a simple and efficient protocol
for fabricating fullerene 1D nanomaterials from bottom-up
strategies is still a challenge.
Recently, surfactant-assisted self-assembly (SAS) has
been recognized as a promising protocol to fabricate organic
nanostructures.[20] In the SAS process, organic units are or-
ganized into different nanostructures with the assistance of
surfactants. Similar to surfactants, low-molecular-weight or-
ganogelators (LMOGs) should possess the potential to fab-
ricate organic nanostructures because of their strong self-as-
sembly ability, and should hence be capable of forming su-
pramolecular gels in certain organic solvents by noncovalent
intermolecular interactions, such as H bonding and p–p
stacking. Although organogelators have been successfully
used to direct the growth of inorganic or hybrid one-dimen-
sional nanomaterials following Shinkaiꢁs pioneering
work,[21,22] supramolecular gel-assisted self-assembly to fabri-
cate fullerene nanostructure is unprecedented.
which assisted fullerene self-assembling into nanorods with
lengths of several micrometers. We have called this method
supramolecular gel-assisted self-assembly (SGAS). Notably,
the bis-urea derived gelator 1[23] was easily synthesized by a
one-step reaction at room temperature in high yield from
methylene diphenyl diisocyanate and octadecylamine. This
easy method may be beneficial to fabricating fullerene
nanorods in large scale for industrial application.
The bis-urea derived gelator 1 could form a thermorever-
sible physical gel in toluene (Figure 2). The thermal charac-
Figure 2. Photographs of gelator 1 gel in toluene (left), and gelator 1–C60
gel in toluene (right).
terization of the gel was carried out by the “vial-inverting
method” to determine Tgel, that is, the temperature at which
the sol-gel is transformed. As shown in Figure S1 in the Sup-
porting Information, Tgel was found to increase from 49 to
668C by raising the concentration of gelator 1 from 2 to
5 wt%. Gelator 1 self-assembled into helical nanobelts with
widths of approximately 50 nm, lengths of several microme-
ters and pitch of about 140 nm, as determined by SEM and
TEM (Figure 3). The results inspired us to anticipate that
co-assembly of fullerene with gelator 1 in toluene might fab-
ricate ordered nanostructures of fullerene, which still remain
a challenge because of the poor dispersibility of fullerene in
common solvents.
Herein, we report the synthesis of supramolecular gel
based on bisACHTUNGTRENNUNG(urea)-derived gelators (Figure 1) with toluene,
[a] Dr. C. Zhang, J. Wang, J.-J. Wang, M. Li, Prof. X.-L. Yang,
Prof. H.-B. Xu
College of Life Science and Technology
National Engineering Research Center for Nanomedicine
Huazhong University of Science and Technology
Wuhan, Hubei, 430074 (P.R. China)
Fax : (+86)27-87792234
E-mail: chunzhang@hust.edu.cn
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201202721.
14954
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 14954 – 14956

COMMUNICATION
Figure 3. a) SEM, and b) TEM images of gelator 1 xerogel in toluene;
scale bars: 500 nm.
As a typical protocol, gelator 1 was dissolved in a toluene
solution of C60 (2 mgmLÀ1) upon being heated at 1108C.
Shortly after being cooled to room temperature a purple
transparent gel was obtained (Figure 2). It should be noted
that encapsulation of C60 molecules could reinforce the
physical gel and increase the Tgel (Figure S2 in the Support-
ing Information). Casting the supramolecular gel onto a
mica plate induced crystallization of fullerene and gelator 1,
which led to the formation of nanorods. As shown in
Figure 4, SEM and TEM analysis displayed that these nano-
Figure 5. a), b) High-resolution TEM images of nanorods formed by gela-
tor 1 and C60 (scale bars: 200 and 10 nm, respectively); and c) the corre-
sponding SAED image.
Figure 4. a) SEM (scale bar: 1 mm), and b) TEM (scale bar: 100 nm)
images of the xerogel prepared from gelator 1/C60 (1:1) in toluene.
rods have an average diameter of several hundred nanome-
ters and length of several micrometers. This morphology is
different from micropolyhedrons yielded by the ambient
crystallization of fullerene from toluene solution (Figure S3
in the Supporting Information).
Scheme 1. Proposed schematic illustration of the formation of nanorods
by SGAS, directed by hydrogen bonding, p–p interactions and van der
Waals forces.
We considered that the ratio between fullerene and gela-
tor 1 might have an important influence on the morphology
of the product. We thus studied the effect of different ratios
of fullerene/gelator 1 on the nanostructure of fullerene.
When the molecular ratio of fullerene/gelator 1 was 1:2, a
mixture of hybrid nanorods and gel helical nanobelts could
be observed. When the ratio was increased to 2:1, the fuller-
ene could not be dissolved completely because of its poor
dispersibility of no more than 3 mgmLÀ1 in toluene.
The high-resolution transmission electron microscopy
(HRTEM) image and selected area electron diffraction
(SAED) pattern indicate that the nanorods are in a crystal-
line state (Figure 5). Moreover, the energy-dispersive X-ray
spectroscopy (EDS) analysis of the nanorods indicated the
presence of nitrogen and oxygen (Figure S4 in the Support-
ing Information). These results suggest that the fullerene
nanorods might be enwrapped by gelator 1.
the supramolecular gel, fullerenes were immobilized in the
gel networks in single-molecule states. During the solvent
evaporation, fullerenes were crystallized orderly in some do-
mains with specific hydrophobic, hydrophilic, and other
weak interactions provided by the strong hydrogen bonding
and p–p interactions between gelators, and therefore
formed into nanorods enwrapped by gelators.
To validate the generality of this supramolecular gel-as-
sisted self-assembly method, we used another bis-urea gela-
tor 2 synthesized in three steps (Scheme S2 in the Support-
ing Information) from diphenyl diisocyanate to co-assemble
with fullerene. Gelator 2 is able to form supramolecular gel
in toluene; the thermal characterization of the gel was car-
ried out as shown in Figures S5 and S6 in the Supporting In-
formation. Using the same protocol as mentioned above, we
could obtain fullerene nonorods, which were characterized
by SEM, TEM, HRTEM and SAED (Figures S7 and S8 in
the Supporting Information).
On the basis of the above-mentioned information, we pro-
pose a possible mechanism for self-assembly (Scheme 1). In
Chem. Eur. J. 2012, 18, 14954 – 14956
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14955

C. Zhang et al.
Universities (HUST-2011TS148) and Wuhan ChenGuang Program
(201150431118). We also thank the Analytical and Testing Center of
Huazhong University of Science and Technology for related analysis.
In summary, we have developed a supramolecular gel-as-
sisted self-assembly method to fabricate fullerene nanorods.
This method might open a door to fabricate low-dimension
nanomaterials based on small organic molecules. Further
studies of the properties of the fullerene nanorods and their
applications are in progress.
Keywords: fullerenes · gels · nanorods · nanomaterials · self-
assembly
Experimental Section
[1] A. Hirsch, M. Brettreich, in Fullerenes, Wiley-VCH, Weinheim,
2005.
Synthesis of gelator 1: The reaction was carried out under nitrogen at-
mosphere. Methylene diphenyl diisocyanate (120 mg, 0.472 mmol) and
octadecylamine (260 mg, 0.963 mmol) was dissolved in CH2Cl2 (20 mL)
and stirred at room temperature for 24 h, until the starting material
could no longer be detected by thin layer chromatography (TLC). The
white precipitate was filtered and washed with methanol; 290 mg (yield:
78%) of white powder with poor solubility in most solvents was ob-
tained. MALDI-TOF-MS: m/z 812 [M+Na+]; IR (KBr): 3328.16,
2920.89, 2849.49, 1633.31, 1595.31, 1563.11 cmÀ1; elemental analysis calcd
(%) for C51H88N4O2: C 77.61, H 11.24, N 7.10; found: C 77.31, H 11.46, N
7.42.
[2] S. S. Babu, H. Mçhwald, T. Nakanishi, Chem. Soc. Rev. 2010, 39,
4021.
[3] M. H. Nurmawati, P. K. Ajikumar, R. Renu, C. H. Sow, S. Valiya-
veettil, ACS Nano 2008, 2, 1429.
[4] J. Geng, W. Zhou, P. Skelton, W. Yue, I. A. Kinloch, A. H. Windle,
B. F. G. Johnson, J. Am. Chem. Soc. 2008, 130, 2527.
[5] H. S. Shin, S. M. Yoon, Q. Tang, B. Chon, T. Joo, H. C. Choi, Angew.
Chem. 2008, 120, 705; Angew. Chem. Int. Ed. 2008, 47, 693.
[6] S. Pekker, A. Jꢃnossy, L. Mihaly, O. Chauvet, M. Carrard, L. Forrꢄ,
Science 1994, 265, 1077.
[7] H. Liu, Y. Li, L. Jiang, H. Luo, S. Xiao, H. Fang, H. Li, D. Zhu, D.
Yu, J. Xu, B. Xiang, J. Am. Chem. Soc. 2002, 124, 13370.
[8] R. Bai, M. Ouyang, Z.-Z. Li, L.-G. Yang, M.-M. Shi, G. Wu, M.
Wang, H.-Z. Chen, J. Mater. Chem. 2008, 18, 4318.
[9] S. I. Cha, K. i. Miyazawa, J.-D. Kim, Chem. Mater. 2008, 20, 1667.
[10] S. Zhou, C. Burger, B. Chu, M. Sawamura, N. Nagahama, M. Toga-
noh, U. E. Hackler, H. Isobe, E. Nakamura, Science 2001, 291, 1944.
[11] T. Kawauchi, J. Kumaki, E. Yashima, J. Am. Chem. Soc. 2006, 128,
10560.
[12] R. Tsunashima, S.-I. Noro, T. Akutagawa, T. Nakamura, H. Kawaka-
mi, K. Toma, Chem. Eur. J. 2008, 14, 8169.
[13] K. Miyazawa, Y. Kuwasaki, A. Obayashi, M. Kuwabara, J. Mater.
Res. 2002, 17, 83.
[14] M. Sathish, K. Miyazawa, T. Sasaki, Chem. Mater. 2007, 19, 2398.
[15] K. Miyazawa, J. Minato, M. Fujino, T. Suga, Diamond Relat. Mater.
2006, 15, 1143.
[16] C. Ringor, K. Miyazawa, T. Awane, Synthesis of C-60 Fullerene
Nanotubes by the Liquid–Liquid Interfacial Precipitation Method,
Materials Research Society Japan-Mrs-J, Tokyo, 2007.
[17] L. Wang, B. Liu, D. Liu, M. Yao, Y. Hou, S. Yu, T. Cui, D. Li, G.
Zou, A. Iwasiewicz, B. Sundqvist, Adv. Mater. 2006, 18, 1883.
[18] L. Wang, B. Liu, S. Yu, M. Yao, D. Liu, Y. Hou, T. Cui, G. Zou, B.
Sundqvist, H. You, D. Zhang, D. Ma, Chem. Mater. 2006, 18, 4190.
[19] T. Tsuchiya, R. Kumashiro, K. Tanigaki, Y. Matsunaga, M. O. Ishit-
suka, T. Wakahara, Y. Maeda, Y. Takano, M. Aoyagi, T. Akasaka,
M. T. H. Liu, T. Kato, K. Suenaga, J. S. Jeong, S. Iijima, F. Kimura,
T. Kimura, S. Nagase, J. Am. Chem. Soc. 2008, 130, 450.
[20] Y. S. Zhao, H. Fu, A. Peng, Y. Ma, Q. Liao, J. Yao, Acc. Chem. Res.
2010, 43, 409.
Synthesis of gelator 2: Methylene diphenyl diisocyanate 3 (2 g, 8 mmol)
and alanine methyl ester hydrochloride (2.42 g, 17.3 mmol) were suspend-
ed in CH2Cl2 (100 mL); dry Et3N (3.5 mL) was added to this suspension.
The mixture was stirred at room temperature, overnight. The white pre-
cipitate was filtered and rinsed with water to give 3.13 g (85.7% yield) of
compound 4 as a white solid. 1H NMR (400 MHz, CDCl3): d=8.49 (2H,
s), 7.26 (4H, J=8.4 Hz, d), 7.04 (4H, J=8.4 Hz, d), 6.49 (2H, J=7.2 Hz,
d), 4.23 (2H, J=7.2 Hz, m), 3.76 (2H, s), 3.64 (6H, s), 1.29 ppm (6H, J=
7.2 Hz, d); 13C NMR (100 MHz, [D6]DMSO): d=173.81, 154.52, 137.88,
134.43, 128.69, 117.75, 51.76, 47.93, 17.77 ppm; EI-MS: m/z: 456 [M+];
IR (KBr): 3307.43, 1734.98, 1631.58, 1566.96 cmÀ1; elemental analysis
calcd (%) for C23H28N4O6: C 60.52, H 6.18, N 12.27; found: C 60.40, H
6.22, N 12.01.
Compound 4 (1.74 g, 3.81 mmol) was dissolved in THF (90 mL), a solu-
tion of KOH (2.2 g, 39.2 mmol) in a mixture of water (9 mL) and metha-
nol (45 mL) was added, then stirred and heated to reflux. The advance-
ment of the reaction was monitored by TLC until no more ester was ob-
served, after 2 h the reaction mixture was concentrated, neutralized with
1N HCl aqueous solution and the precipitate was filtered and dried in
vacuum for 12 h to obtain 5 (1.48 g, 91%) as a white powder, which was
used directly without purification. Compound 5 (444 mg, 1.04 mmol), oc-
tadecylamine (643.8 mg, 2.39 mmol), EDC (467.8 mg, 2.44 mmol) and
NHS (512.4 mg, 4.3 mmol) were dissolved in DMSO (120 mL) and stirred
for 24 h at room temperature. The reaction mixture was poured into a
large amount of water, then filtered, washed with CH2Cl2 to obtain
740 mg gelator 2 (76% yield) as a white solid. MALDI-TOF-MS: m/z:
952 [M+Na+]; IR (KBr): 3281.70, 2920.22, 2851.28, 1633.02, 1605.69,
1564.57 cmÀ1; elemental analysis calcd (%) for C57H98N6O4: C 73.50, H
10.61, N 9.02; found: C 73.83, H 10.80, N 9.38.
[21] Y. Ono, K. Nakashima, M. Sano, Y. Kanekiyo, K. Inoue, J. Hojo, S.
Shinkai, Chem. Commun. 1998, 1477.
[22] K. J. C. van Bommel, A. Friggeri, S. Shinkai, Angew. Chem. 2003,
115, 1010–1030; Angew. Chem. Int. Ed. 2003, 42, 980–999, and ref-
erences therein.
Acknowledgements
[23] K. Hanabusa, K. Shimura, K. Hirose, M. Kimura, H. Shirai, Chem.
Lett. 1996, 885.
This work was supported by the National Natural Science Foundation of
China (20902031), the National Basic Research Program (2012CB932500
and 2011CB933103), the Fundamental Research Funds for the Central
Received: July 29, 2012
Revised: October 5, 2012
Published online: October 30, 2012
14956
www.chemeurj.org
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 14954 – 14956