Multiple hydrogen-bond-induced supramolecular nanostructure from a pincer-like molecule and a [60]fullerene derivative

Article abstract of DOI:10.1016/j.tet.2005.06.112

A new supramolecular self-assembled system between a perylene bisimide bearing diaminopyridine-substituted isophthalamide groups (PP) and a [60]fullerene containing barbituric acid moiety (C₆₀bar) through a complementary six-point hydrogen-bonding interaction was constructed. The formation of hydrogen bonding was confirmed by ¹H NMR spectra studies in CDCl₃. Fluorescence quenching experiments indicated that the fluorescence of PP was greatly quenched by the hydrogen-bonded C₆₀bar (K_sv=2.71×10⁴ M^-1). A steady and rapid cathodic 0.15 μA cm^-2 photocurrent response of the PP/C ₆₀bar film deposited onto an ITO electrode was produced under the irradiation of 20 mW cm^-2 white light, indicating the presence of photo-induced electron transfer between PP and C₆₀bar. TEM images showed that spherical particles were fabricated by the self-assembly of PP and C₆₀bar through hydrogen-bonding interaction.

Full text of DOI:10.1016/j.tet.2005.06.112

Tetrahedron 61 (2005) 8686–8693
Multiple hydrogen-bond-induced supramolecular nanostructure
from a pincer-like molecule and a [60]fullerene derivative
Junpeng Zhuang, Weidong Zhou, Xiaofang Li, Yongjun Li, Ning Wang, Xiaorong He,
*
Huibiao Liu, Yuliang Li, Li Jiang, Changshui Huang, Shuang Cui, Shu Wang and Daoben Zhu
*
CAS Key Laboratory of Organic Solids, Center for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100080, People’s Republic of China
Received 11 April 2005; revised 27 June 2005; accepted 29 June 2005
Abstract—A new supramolecular self-assembled system between a perylene bisimide bearing diaminopyridine-substituted isophthalamide
groups (PP) and a [60]fullerene containing barbituric acid moiety (C60bar) through a complementary six-point hydrogen-bonding
interaction was constructed. The formation of hydrogen bonding was confirmed by 1H NMR spectra studies in CDCl3. Fluorescence
quenching experiments indicated that the fluorescence of PP was greatly quenched by the hydrogen-bonded C60bar (KsvZ2.71!104 MK1).
A steady and rapid cathodic 0.15 mA cmK2 photocurrent response of the PP/C60bar film deposited onto an ITO electrode was produced
under the irradiation of 20 mW cmK2 white light, indicating the presence of photo-induced electron transfer between PP and C60bar. TEM
images showed that spherical particles were fabricated by the self-assembly of PP and C60bar through hydrogen-bonding interaction.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
Hydrogen bonds are among the most useful interactions to
encourage the self-assembly of molecules into well-defined
aggregates and to order an ensemble of molecules
spontaneously into larger and more complex structure.12
The strength and selectivity of hydrogen bonds can be
improved by introducing arrays of donor (D) and acceptor
(A) sites. Arrays of two and three hydrogen bonds have
already been studied, and the self-complementary quadruple
hydrogen bonds (DDAA) derived from diaminotriazines
or diaminopyrimidines have also been studied for their
high dimerization constants.13 The self-assembly between
cyanuric or barbituric acid wedge (ADA–ADA array) and a
corresponding diaminopyridine-substituted isophthalamide
receptor (DAD–DAD array) provided six-point hydrogen
bonds, which made them attractive for molecular recog-
nition studies, supramolecular polymer, and self-assembly
of multi-chromophores.14
The [60]fullerene molecule has unique and attractive
electronic, optical, and mechanical properties owing to its
chemical properties and uniform, spherical, and nanoscale
physical structure.1 In order to develop fullerene-containing
supramolecular assemblies and advanced materials,2
[60]fullerene has been incorporated into multi-component
molecular systems such as porphyrins,3 rotaxanes,4 and
catenanes.5 The encouraging properties of these [60]fuller-
ene hybrids have attracted much more interests in the
construction of even more complex two- and three-
dimensional systems. And the self-assembly of [60]fuller-
ene-based molecules has been found to be an efficient way
to construct nanoscale aggregates with specific properties.6
p-Conjugated perylene bis-imides represent one of the most
thoroughly studied classes of organic semiconductors with a
variety of different structures,7 with possible applications
such as fluorescent solar collectors,8 photovoltaic devices,9
dye lasers,10 and molecular switches.11 These dyes have
outstanding chemical, thermal, and photochemical stability,
which offers great opportunities for preparing new
materials.
In our previous work based on the hydrogen-bonded
supramolecular systems of [60]fullerene, we reported the
self-assembly of 2,6-di(acylamino)pyridine-substituted [60]
fullerene derivative with 1-dodecyluracil,15a,b perylene
bisimide derivative15c and PPV derivative15d by three-
point hydrogen-bonding interactions. These molecules
tended to form stable nanoscale aggregates. Their energy
and electron-transfer processes were investigated. Bassani
et al. reported the facile synthesis of a fullerene-barbituric
acid from C60 and 5-bromobarbituric acid by a modified
Keywords: Hydrogen bond; Fullerene; Supramolecular.
*
Corresponding authors. Tel.: C86 10 62588934; fax: C86 10 82616576;
e-mail: ylli@iccas.ac.cn
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.06.112

J. Zhuang et al. / Tetrahedron 61 (2005) 8686–8693
8687
Scheme 1. Supramolecular system of hydrogen-bonded self-assembly of PP/C60bar with a 3D model.
Bingel reaction.16 This reaction introduced six hydrogen-
bonding sites of a barbituric acid into [60]fullerene in one
step. These sites were non-self-complementary, and their
spatial arrangement made the fullerene-barbituric acid well
suitable for the construction of fullerene-containing archi-
tectures. Although the structure of this fullerene-barbituric
acid was novel, the poor solubility of this compound
limited its application in supramolecular chemistry studies.
In this paper, we introduced barbituric acid into [60]fuller-
ene-di[2-(2-butoxy-ethoxy)-ethyl] malonate (C60mal) to
form a novel fullerene derivative (C60bar) with excellent
solubility in organic solvents. We also synthesized a
perylene bisimide (PP) with two diaminopyridine-substi-
tuted isophthalamide groups for the formation of a pincer-
like structure in order to increase hydrogen-bonding
interaction. Because the association constant between the
barbituric acid ring and the diaminopyridine-substituted
ethoxy)-ethyl] malonate by Bingel reaction using CBr4 and
DBU in toluene.17 C60bar was synthesized from C60mal
and 5-bromobarbituric acid according to the literature
method.16 The crude product was worked up on silica gel
using a mixture of toluene/MeOH (v/v, 10:1) as the eluent,
and the second band was collected to give C60bar. The
C60bar had excellent solubility in toluene and CHCl3,
owing to the introduction of di[2-(2-butoxy-ethoxy)-ethyl]
malonate into the fullerene-barbituric acid structure, there-
fore, greatly facilitated its application Scheme 2.
The cyclopropanation of C60 with two addends afforded
mixed bisadducts, where e and trans-3 isomers were the
main products.18 In this work, the barbituric acid ring was
introduced into C60 as the second addend. The product
C60bar contained position isomers. However, here we try to
use C60bar as a building block for the construction of
supramolecular assemblies, the trans-3 and e isomers could
form same supramolecular structure with diaminopyridine-
substituted isophthalamide group by hydrogen-bonding
interaction.
isophthalamide receptors was in the range of 104–105 MK1 14
,
the supromolecular assembly of C60bar and PP exhibited
strong interaction and formed uniform aggregates.
(Scheme 1)
MALDI-TOF MS spectra of C60bar showed three peaks,
1237.3 (MC), 1110.4 (MCKbarbituric acid ring) and 720.1
(MCKbarbituric acid ring-bis[2-(2-butoxy-ethoxy)-ethyl]
malonate). H NMR spectra showed two broad peaks at d
9.3 and 11.1, which were assigned to the resonance of the
2. Results and discussion
1
The synthesis of PP and C60bar was sketched in Scheme 1.
C60mal was synthesized from C60 and di[2-(2-butoxy-

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J. Zhuang et al. / Tetrahedron 61 (2005) 8686–8693
Scheme 2. Synthesis of C60bar and PP. (a) CBr4, DBU, toluene, rt, 2 h, 44%; (b) DBU, toluene/DMSO (v/v, 95:5), rt, 7 h, 12%; (c) THF, reflux, 4 h;
(d) pyridine, THF, 0–10 8C, 7 h, 56%; (e) K2CO3, 18-crown-6, toluene, 80 8C, 4 h, 88%.
imidic protons of barbituric acid ring. Because C60bar was
an isomeric mixture, the signals of imidic protons appeared
at different positions and are rather broad.
C60bar. When C60bar was mixed with 0.5 equiv PP
(stoichiometric ratio), significant downfield shifts were
observed for the resonance of the imidic protons of C60bar
(from d 9.3 and 11.1 to 13.2). These shifts showed that
strong hydrogen bonding took place between C60bar and
PP.
N,N0-di(6-butyrylamino-pyridin-2-yl)-5-hydroxy-isophthal-
amide (DAP) was synthesized from N-butyryl-2,6-diamino-
pyridine, 5-hydroxy-benzene-1,3-dicarbonyl chloride and
pyridine in anhydrous THF. 1,7-dibromo-N,N0-di(2,6-diiso-
propyl-phenyl)perylenediimine (BP) was synthesized
according to a known method.19 PP was obtained by the
nucleophilic reaction of BF, DAP and K2CO3 in anhydrous
toluene in the presence of 18-crown-6.20
1
The H NMR spectra changes of PP with increasing the
concentration of C60bar were also recorded in CDCl3. The
concentration of PP was kept constant (6 mmol/L), and
the concentration of C60bar was increased gradually (from
0 to 12 mmol/L). As shown in Figure 1B, the signals at d 8.5
and 7.8, assigned for the two amidic protons of the
diaminopyridine-substituted isophthalamide unit, were
observed before the addition of C60bar. When the
concentration of C60bar was increased, the signals for the
two amidic protons became broad and shifted to lower
magnetic fields. When the concentration of C60bar was
increased to 12 mmol/L, the signals for the two amidic
protons shifted downfield to d 9.8 and 8.8, respectively. And
the 2-proton of the isophthalic acid group, which positioned
close to the 2-CO of the barbiturate ring, also shifted
downfield by 0.25 ppm from d 8.20 to 8.45. All the spectra
changes of the C60bar and PP in the titration experiment
showed the formation of multiple hydrogen-bonding
interaction between PP and C60bar.
The formation of hydrogen-bonded self-assembly of C60bar
and PP was demonstrated by 1H NMR spectroscopic
studies. Titration experiment in CDCl3 between the
diaminopyridine-substituted isophthalamide group and
complementary barbiturate substrate led to the character-
istic changes in the 1H NMR spectra of the two components,
which confirmed the formation of hydrogen-bonded self-
1
assembly.14 The H NMR spectra changes of C60bar with
increasing PP concentration were recorded. Figure 1A
showed the partial 1H NMR spectra of C60bar (12 mmol/L)
and C60barCPP (12 and 6 mmol/L). Two broad peaks at d
9.3 and 11.1 were observed, which were assigned to the
resonance of the imidic protons of the barbituric ring of

J. Zhuang et al. / Tetrahedron 61 (2005) 8686–8693
8689
Figure 1. Partial 1H NMR spectra of PP/C60bar supramolecular system in CDCl3 at rt. (A) the concentration of C60bar was kept constant (12 mmol/L), and
the concentration of PP was 0 and 6 mmol/L, respectively; (B) the concentration of PP was kept constant (6 mmol/L), and the concentration of C60bar was
increased gradually (from 0 to 12 mmol/L).
F0
F
The fluorescence quenching experiment of PP by C60bar
was carried out in chloroform. The concentration of PP was
kept constant at 1!10K5 mol/L and the concentration of
C60bar was increased gradually. Because of the compe-
tition absorptions of C60bar at the excitation and emission
wavelength of PP, the fluorescence intensities were
calibrated according to the literature method.21 The
dependence of the fluorescence intensity of PP on the
concentration of C60bar follows the Stern–Volmer
equation. [Eq. 1],22 in which F0 is the fluorescence intensity
of PP without the addition of C60bar, F is the calibrated
fluorescence intensity of PP upon the addition of C60bar,
Ksv is the quenching constant, and [Q] is the concentration
of C60bar.
Z 1 CKsv½Qꢀ
1
As shown in Figure 2A, PP showed a strong emission band
at 561 nm and a shoulder band at 600 nm with the excitation
wavelength at 490 nm. The fluorescence of PP was strongly
quenched with the addition of C60bar. The Stern–Volmer
constant (Ksv) is 2.71!104 MK1
.
For comparison, the fluorescence quenching experiment of
PP by C60mal, which would not form hydrogen bonds with
PP was also performed. Figure 2B showed the fluorescence
spectra of PP (1!10K5 M, solid line) and PPCC60mal
(1!10K5 and 2!10K5 M, dash line). We found the
Figure 2. (A) The fluorescence spectra of PP ([PP]Z1!10K5 M) in chloroform with increasing concentration of C60bar: 0.0 (0), 1!10K6 M (1), 2!10K6
M
(2), 4!10K6 M (3), 8!10K6 M (4), 1.2!10K5 M (5), 2!10K5 M (6), 4!10K5 M (7); (B) The fluorescence spectra of PP (1!10K5 M, solid line) and a
mixture of PPCC60mal (1!10K5 M and 2!10K5 M, dash line) in chloroform. Excitation wavelength was 490 nm.

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J. Zhuang et al. / Tetrahedron 61 (2005) 8686–8693
hydrogen-bonding interaction between PP and C60bar
played an important role in the fluorescence quenching.
These results indicated that there existed intermolecular
charge transfer between the supramolecular system of PP
and C60bar by hydrogen-bonding interaction.
A conventional three-electrode cell was used to measure the
photoelectrochemical properties of the self-assembled PP/
C60bar film.23 The photocurrent generation of PP/C60bar
film deposited onto an ITO electrode was measured at
20 mW cmK2 white light irradiation. When the irradiation
was switched on and off, a steady and rapid cathodic
0.15 mA cmK2 photocurrent response of the PP/C60bar film
was produced. Four cycles of the photocurrent generation
were shown in Figure 3, which showed that the response to
on–off cycling was prompt and reproducible. The photo-
current stability in the system was rather good during the
monitored time.
Figure 3. Photocurrent generation of the PP/C60bar supramolecular
assembly film upon the irradiation of white light (20 mW/cm2) in 0.5 M
KCl solution without bias voltage.
Our group has reported the self-assembly of [60]fullerene
containing 2,6-di(acylamino) pyridine unit with 1-dodecyl-
uracil and perylene bis-imides derivative. These hydrogen-
bonded supramolecular systems formed spherical nano-
aggregates observed by SEM and TEM.15a,b,c Some
hydrogen-bonded supramolecular system containing peryl-
ene derivatives were also reported to form well-defined
fluorescence of PP was almost unchanged upon the addition
of 2 equiv C60mal. Consider the competition absorptions of
C60mal at the excitation and emission wavelength of PP, we
might conclude that the fluorescence of PP was not affected
with the addition of C60mal. This suggested that the
Figure 4. Transmission electron micrograph and size distribution histogram of assemblies resulting from evaporation of 10K5 M PP/C60bar in CHCl3.

J. Zhuang et al. / Tetrahedron 61 (2005) 8686–8693
8691
nano-fibrous structures.24 Consider the self-assembly beha-
vior of PP with C60bar, we can assume that certain three-
dimensional supramolecular structures stabilized by the
intermolecular hydrogen bonding through barbituric acid
groups and diaminopyridine-substituted isophthalamide
moieties was formed. Figure 4 showed the transmission
electron micrographs (TEM) of C60bar/PP self-assembled
on a carbon-coated copper grid after evaporation of CHCl3
solvent and the corresponding size distribution histogram.
Spherical particles could be observed and the diameters of
these particles were in the range of 5–25 nm with a mean
diameter of 12 nm. [60]Fullerene derivatives had high
aggregation tendency because of the strong p–p stacking of
the carbon cage,25 and the perylene ring also showed strong
intermolecular p–p stacking,24 which led to the formation
of spherical particle aggregates of the hydrogen-bonded
PP/C60bar supramolecular structure.
ratio of PP and C60bar is 1:2) for 30 min and dried in N2
stream.
4.1.1. Synthesis of DAP. N-butyryl-2,6-diaminopyridine
(600 mg, 3.35 mmol) and freshly distilled pyridine (323 mL,
4 mmol) were dissolved in anhydrous THF (30 mL). The
reaction mixture was cooled to 0–10 8C with ice water bath.
After degassing for 10 min, 5-hydroxy-benzene-1,3-dicar-
bonyl chloride (360 mg, 1.65 mmol) dissolved in 10 mL
anhydrous THF was added dropwise over 1 h. After stirring
for 6 h at rt, 20 mL water was added and the reaction
mixture was stirred for additional 20 min. THF was then
removed under reduced pressure and the resulting precipi-
tate was filtered, washed several times with water, dried at
rt, and purified by column chromatography using CHCl3/
MeOH (v/v, 100:1) as the eluent to give DAP as a white
powder. Yield: 463 mg, 56%; IR (KBr): 3370, 3280, 2965,
2875, 1672, 1586, 1516, 1450, 1295, 1242, 1156, 1084,
1
801 cmK1; H NMR (DMSO-d6): d 10.30 (s, 2H), 10.15
3. Conclusions
(s, 1H), 10.05 (s, 2H), 7.97 (s, 1H), 7.81–7.72 (m, 6H), 7.49
(s, 2H), 2.36 (t, JZ7.2 Hz, 4H), 1.62–1.55 (m, 4H), 0.88
(t, JZ7.2 Hz, 6H) ppm MS: m/z (EI, 70 eV) 504 [MC].
Anal. Calcd for C26H28N6O5: C, 61.89; H, 5.59; N, 16.66;
Found C, 61.64; H, 5.65; N, 16.59%.
In conclusion, a novel pincer-like molecule PP was
synthesized and the supramolecular system between PP
and C60bar through a six-point hydrogen-bonding inter-
1
action was fabricated. H NMR and fluorescence measure-
ments indicated that strong hydrogen-bonding interaction
took place between PP and C60bar. The photocurrent
generated by the self-assembled film was measured, and a
cathodic photocurrent response of 0.15 mA cmK2 at
20 mW cmK2 white light irradiation was obtained. TEM
images of PP/C60bar aggregates showed spherical particles
having a mean diameter of 12 nm. These bichromophoric
assemblies could be of importance for potential applications
in photovoltaic and nanoscale devices.
4.1.2. Synthesis of PP. BP (104 mg, 0.12 mmol), DAP
(140 mg, 0.278 mmol), K2CO3 (100 mg, 0.73 mmol) and
18-crown-6 (50 mg, 0.19 mmol) were dissolved in anhy-
drous toluene (20 mL). The reaction mixture was degassed
for 10 min and then heated to 80 8C. After stirring for 4 h,
nearly all the BP was consumed (monitored by TLC), the
solvent was removed under reduced pressure and the residue
was purified by column chromatograph on silica gel using
CH2Cl2/MeOH (v/v, 100:1) as the eluent to give PP as a red
solid. Yield: 181 mg, 88%. UV–vis (CHCl3): lmax(3)Z302
(70220), 389 (8610), 491 (36600), 525 nm (55510 molK1
dm3 cmK1); fluorescence (CHCl3): lmaxZ561 nm; IR
(KBr): 3305, 3067, 2965, 2931, 1704, 1667, 1588, 1511,
1448, 1404, 1338, 1306, 1247, 1156, 1078, 961, 902, 799,
4. Experimental
4.1. General
1
739 cmK1; H NMR (CDCl3): d 9.53 (d, JZ8.4 Hz, 2H),
8.75 (d, JZ8.4 Hz, 2H), 8.52 (br s, 4H), 8.44 (s, 2H), 8.21
(s, 2H), 7.93–7.87 (m, 12H), 7.81 (br s, 2H), 7.69 (t, JZ
8.1 Hz, 4H), 7.46 (t, JZ7.8 Hz, 2H), 7.30 (d, JZ7.5 Hz,
4H), 2.77–2.72 (m, 4H), 2.29 (t, JZ7.2 Hz, 8H), 1.75–1.67
(m, 8H), 1.15–1.11 (m, 24H), 0.97 (t, JZ7.2 Hz, 12H) ppm;
MALDI-TOF MS: Calcd for C100H94N14O14 (MC), m/zZ
1714.7; found 1714.8.
Reagents were purchased from Acros or Aldrich Corpo-
ration and were utilized as received unless indicated
otherwise. All solvents were purified using standard
procedures.
UV–vis and fluorescence spectra were measured on a
Hitachi U-3010 and Hitachi F-4500 spectrometer, respect-
ively. IR spectra were recorded as KBr pellets on a Perkin-
Elmer System 2000 spectrometer. 300 MHz 1H NMR
spectra were recorded on a Bruker dm!300 spectrometers.
MALDI-TOF mass spectrometric measurements were
performed on Bruker Biflex III MALDI-TOF. Transmission
electron micrographs (TEM) were collected on a JEOL JEM
2010 instrument.
4.1.3. Synthesis of C60mal. C60 (250 mg, 0.35 mmol) and
CBr4 (166 mg, 0.5) were dissolved in anhydrous toluene
(150 mL) with vigorous stirring. After degassing for 15 min,
di[2-(2-butoxy-ethoxy)-ethyl] malonate (196 mg, 0.5 mmol)
and DBU (150 mL, 1 mmol) were added and the mixture
color changed gradually from purple to dark red. After
stirring for 2 h, the solvent was removed under reduced
pressure. The residue was purified by column chromato-
graphy using toluene/ethyl acetate (v/v, 10:1) as the eluent
to give C60mal as a brown solid. Yield: 170 mg, 43.8%; IR
(KBr): 2954, 2927, 2864, 1746, 1429, 1378, 1232, 1113,
The photocurrent generation measurement was carried out
using a platinum wire as a counter electrode and the
saturated calomel electrode as a reference electrode.
A solution of 0.5 M KCl was selected as the supporting
electrolyte in the measurements. The ITO plates were
cleaned by repeated sonication in isopropyl alcohol and in
deionized water. The dry ITO plates were immersed into a
chloroform solution of PP/C60bar (1!10K3 mol/L, molar
1
1031, 706, 527 cmK1; H NMR (CDCl3): d 4.65 (t, JZ
4.8 Hz, 4H), 3.88 (t, JZ4.8 Hz, 4H), 3.68 (t, JZ4.8 Hz,
4H), 3.57 (t, JZ4.8 Hz, 4H), 3.45 (t, JZ6.8 Hz, 4H), 1.58–
1.53 (m, 4H), 1.39–1.33 (m, 4H), 0.91 (t, JZ7.2 Hz, 6H)

8692
J. Zhuang et al. / Tetrahedron 61 (2005) 8686–8693
ppm; MALDI-TOF MS: Calcd for C79H34O8 (MC), m/zZ
1110.2; found 1110.1.
D. I.; Li, K.; Guldi, D. M.; Ramey, J. Org. Lett. 2004, 6,
1919–1922.
6. (a) Kimura, M.; Saito, Y.; Ohta, K.; Hanabusa, K.; Shirai, H.;
Kobayashi, N. J. Am. Chem. Soc. 2002, 124, 5274–5275.
(b) Carano, M.; Corvaja, C.; Garlaschelli, L.; Maggini, M.;
Marcaccio, M.; Paolucci, F.; Pasini, D.; Righetti, P. P.; Sartori,
E.; Toffoletti, A. Eur. J. Org. Chem. 2003, 374–384.
(c) Nierengarten, J.-F. Chem. Eur. J. 2000, 6, 3667–3670.
(d) Hasobe, T.; Kashiwagi, Y.; Absalom, M. A.; Sly, J.;
Hosomizu, K.; Crossley, M. J.; Imahori, H.; Kamat, P. V.;
Fukuzumi, S. Adv. Mater. 2004, 16, 975–979. (e) Sun, D.;
Tham, F. S.; Reed, C. A.; Chaker, L.; Boyd, P. D. W. J. Am.
Chem. Soc. 2002, 124, 6604–6612.
4.1.4. Synthesis of C60bar. C60mal (111 mg, 0.1 mmol)
and 5-bromobarbituric acid (21 mg, 0.1 mmol) were
dissolved in toluene/DMSO (v/v, 95:5, 150 mL) with
vigorous stirring. After degassing for 15 min, DBU
(20 mL, 0.2 mmol) was added. After stirring at rt for 2 h,
the reaction mixture was washed with water (60!3 mL).
The organic layer was separated and dried over anhydrous
Na2SO4. The solvent was then removed under reduced
pressure. The residue was purified by column chromato-
graphy on silica gel using CHCl3/MeOH (v/v, 10:1) as the
eluent to give C60bar as a brown solid. Yield: 17 mg, 12%;
IR (KBr): 3173, 2955, 2925, 2857, 1744, 1663, 1541, 1457,
1377, 1245, 1114, 1031, 880, 766 cmK1; 1H NMR (CDCl3):
d 11.1 (br), 9.3 (br), 4.6–4.5 (br, 4H), 3.7–3.4 (br, 16H), 1.5–
0.8 (br, 14H) ppmK1. MALDI-TOF MS: Calcd for
C83H36O11 (MC), m/zZ1236.23; found 1237.3 (MCCH),
1110.4 (MCKbarbituric acid), 720.1 (MCKbarbituric acid
ring-bis[2-(2-butoxy-ethoxy)-ethyl] malonates).
7. (a) Mu¨ller, G. R. J.; Meiners, C.; Enkelmann, V.; Geerts, Y.;
Mu¨llen, K. J. Mater. Chem. 1998, 8, 61–64. (b) van de Craats,
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This work was supported by the National Natural Science
Foundation of China (20131040, 50372070, 20418001 and
20473102) and Major State Basic Research Development
Program.
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