Self-assembly and characterization of a novel hydrogen-bonded nanostructure

Article abstract of DOI:10.1021/jp0373853

A novel hydrogen-bonded supramolecular system of a [60]fullerene derivative with perylene bisimide was synthesized and characterized. ¹H NMR spectra confirmed the existence of strong hydrogen-bonding interaction between compounds 1 and 5. Transmission electron microscopy images of 1-5 aggregates showed spherical particles having a mean diameter of 50 nm. The photocurrent response of the film was measured, and a steady and rapid anodic photocurrent response was obtained.

Full text of DOI:10.1021/jp0373853

6256
J. Phys. Chem. B 2004, 108, 6256-6260
Self-Assembly and Characterization of A Novel Hydrogen-Bonded Nanostructure
Yang Liu,†,‡ Shengqiang Xiao,†,‡ Hongmei Li,†,‡ Yuliang Li,*,† Huibiao Liu,† Fushen Lu,†,‡
Junpeng Zhuang,† and Daoben Zhu*,†
CAS Key Laboratory of Organic Solids, Center for Molecular Sciences, Institute of Chemistry, and
Graduate School, Chinese Academy of Sciences, Beijing 100080, People’s Republic of China
ReceiVed: NoVember 6, 2003; In Final Form: March 11, 2004
A novel hydrogen-bonded supramolecular system of a [60]fullerene derivative with perylene bisimide was
synthesized and characterized. 1H NMR spectra confirmed the existence of strong hydrogen-bonding interaction
between compounds 1 and 5. Transmission electron microscopy images of 1‚5 aggregates showed spherical
particles having a mean diameter of 50 nm. The photocurrent response of the film was measured, and a
steady and rapid anodic photocurrent response was obtained.
Introduction
of the perylene bisimide 5 is sketched in Scheme 1. Briefly,
1,6,7,12-tetrachloroperylene-3,4,9,10-tetracarboxylic acid dian-
hydride (2) was converted to the corresponding n-octyl bisimide
3 using n-octylamine. Subsequently, compound 4 was prepared
by the nucleophilic substitution of the four chlorine atoms using
4-(n-octyloxy)phenol. The perylene bisimide 5 was synthesized
by cleavage of the bisimide 4 and reaction with ammonium
acetate, according to known methods.8
In the past few years, new photoelectric materials containing
conjugated organic molecules have attracted commercial and
scientific interest.1 Design and self-assembly of organic mol-
ecules into functional superstructures is a main goal in sup-
ramolecular chemistry. Control of hydrogen bonding has at-
tracted much attention in the design of various molecular
assemblies by virtue of the directionality and specificity.2 Well-
defined nanosized aggregates should be very useful for the
development of novel functional materials and nanoelectronic
devices. Hydrogen-bonding assemblies are most promising to
fabricate a controllable molecular array and shape for efficient
intermolecular energy and electron transfer between donor and
acceptor units.3,4 The ready availability of [60]fullerene and its
derivatives as novel electropool π-systems has increasingly
invited exploration of their outstanding physical and chemical
properties.5 Of particular interest is the hydrogen-bonding
assembly by organic molecules of organofullerene molecules
containing [60]fullerene, combination of the pyridine unit and
carboxylic acid moiety to provide stable hydrogen-bonded
molecular assemblies.
In this paper we discuss the self-assembly and characterization
of [60]fullerene derivative 1 and perylene bisimide 5 to form a
novel hydrogen-bonded supramolecular system in which three
amino functionalities of the [60]fullerene moiety positioned on
the assembly interact with perylene bisimide via amino-
carboxylic acid interaction (Chart 1). Many organic systems have
been developed that exhibit reasonable light-harvesting efficien-
cies, and much has been shown about the energy and electron
transfer. And these systems provide effective means to convert
photons to electrons.6 We hope that the aggregate obtained by
complextion of 1 and 5 through hydrogen bonding would be a
good candidate for efficient intermolecular energy and electron
transfer.
The formation of the hydrogen-bonding self-assembly of 1
1
and 5 was demonstrated by H NMR spectroscopic studies.
Upon complexation of compound 5 by compound 1, the imide
proton signal of 5 underwent a significant downfield shift of
several parts per million in the NMR titration experiment since
the electron densities of the protons involved in hydrogen bonds
were decreased and consequently their NMR signals were
shifted to lower magnetic fields. The interaction of 5 with
compound 1 was investigated by 1H NMR spectroscopic titration
carried out in CDCl3. For the 1H NMR studies, the concentration
of 5 was kept constant and the change in the chemical shift
was followed as a function of increasing concentration of 1.
The NMR titration experiments revealed a significant downfield
shift of the amidic proton signal because of complexation of 1
(Figure 1). The peak at δ ) 8.39 ppm was assigned to the N-H
protons of compound 5. When compound 5 (1 × 10-5 M) was
blended with 0.5 equiv of compound 1 in CDCl3, the chemical
shift for the proton resonance of the amidic protons of compound
5 changed from 8.39 to 8.73 ppm. When compound 5 (1 ×
10-5 M) was blended with 1, 1.5, and 2 equiv of compound 1
in CDCl3, the chemical shift for the proton resonance of the
amidic protons of 5 changed from 8.39 to 8.94, 9.23, and 9.47
ppm, respectively. We also measured a mixture solution of
compound 5 (1 × 10-5 M) and 2.5 equiv of compound 1 in
CDCl3, and found that the chemical shift for the proton
resonance of the amidic protons of compound 5 changed from
8.39 to 9.69 ppm. These changes are characteristic of the
formation of a multiple-point hydrogen-bonding complex. As
shown in Figure 2, analysis of the downfield shift of the amidic
protons of compound 5 as a function of increasing concentration
of 1 provided support for the 1:2 binding model. These results
showed that strong hydrogen bonding took place between 1 and
5, and these assembly motifs exhibited a significantly high
stability.
Results and Discussion
The [60]fullerene derivative 1 bearing a 2,6-diacylaminopyr-
idine unit was prepared as previously reported.7 The synthesis
* To whom correspondence should be addressed. E-mail: ylli@iccas.ac.cn.
† Center for Molecular Sciences, Institute of Chemistry.
‡ Graduate School.
10.1021/jp0373853 CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/20/2004

A Novel Hydrogen-Bonded Nanostructure
J. Phys. Chem. B, Vol. 108, No. 20, 2004 6257
CHART 1: Superstructure of Self-Assembly of [60]Fullerene Derivative 1 with Perylene Bisimide 5 by Hydrogen
Bonding
SCHEME 1: Synthesis of Perylene Compoundsa
a Reagents and conditions: (a) n-octylamine, propionic acid, reflux, 24 h; (b) 4-(n-octyloxy)phenol, K2CO3, N-methyl-2-pyrrolidinone (NMP),
reflux, argon, 24 h; (c) KOH, 2-propanol/water, reflux, argon, 42 h; (d) ammonium acetate, propionic acid, reflux, 24 h.
As shown in Figure 3, the FT-IR spectra of 1 and 5 in CH2-
Cl2 showed the free NH stretching band at 3344 and 3173 cm-1
As shown in Figure 5a, pure perylene bisimide 3 showed
intense fluorescence, and the fluorescence of compounds 4 and
5 showed significant quenching compared with that of com-
pound 3. Pure perylene bisimides 4 and 5 showed weak
fluorescence. This is due to the p-octyloxy group of compounds
4 and 5, leading to strong fluorescent quenching.3a,8f We also
found that when compound 5 was added with compound 1 in
CHCl3 at different ratios ([1]:[5] ) 1:1 or 2:1 stoichiometry),
the fluorescence of 5 was quenched slightly by the organo-
fullerene (Figure 5b). These results indicated there was intramo-
lecular and intermolecular charge transfer between the octyloxy
group and perylene bisimide moiety and between the perylene
bisimide and the organofullerene in these systems.
,
respectively. The NH stretching band of the mixture of 1 and 5
(2:1 stoichiometry) in CH2Cl2 was observed at 3280 cm-1,which
is consisted with the formation of hydrogen bonding between
1 and 5. These results indicated that a three-point hydrogen
bonding between 1 and 5 is formed.
In UV/vis titration experiments, the concentration of 5 was
kept constant upon addition of 1 in chloroform at different ratios.
The absorption spectrum of 1 has a weak peak at 423 nm which
is characteristic of a [6,6]-closed fullerene structure and no
absorption at wavelengths λ > 450 nm.7 As shown in the UV/
vis spectra (Figure 4), although no obvious shifts of 5 upon
addition of 1 are observed, absorption intensities of 1:1 and
1:2 complexes of 5 with 1 exhibit distinct changes due to
hydrogen-bonding interaction of 1‚5. A similar phenomenon was
mentioned by Wu¨rthner et al.4
Photocurrent generation of a perylene bisimide 5 and [60]-
fullerene derivative 1 film ([1]:[5] ) 2:1 stoichiometry)
deposited onto an ITO electrode was measured at 63.2 mW/
cm2 white light irradiation. A steady and rapid anodic 0.07 µA

6258 J. Phys. Chem. B, Vol. 108, No. 20, 2004
Liu et al.
Figure 4. Changes in the UV/vis absorbance of 5 (the concentration
of 5 was kept constant at 1 × 10-5 mol/L) upon addition of 1 in CHCl3
at different ratios ([1]:[5] ) 1:1 or 2:1 stoichiometry).
1
Figure 1. Partial H NMR spectra of the 1‚5 supramolecular system
in different concentration ratios in CDCl3 at room temperature. The
concentration of 5 was kept constant at 1 × 10-5 M.
Figure 2. 1H NMR binding isotherm for 5 with 1 in CDCl3 at room
temperature. The concentration of 5 was kept constant at 1 × 10-5 M.
Figure 5. (a) Fluorescence spectra of compounds 3-5 at 1 × 10-5
mol/L in CHCl3 (λem ) 467 nm). (b) Fluorescence titration experiment
of 5 (the concentration of 5 was kept constant at 1 × 10-5 mol/L)
upon addition of 1 in CHCl3 (λem ) 467 nm) at different ratios ([1]:[5]
) 1:1 or 2:1 stoichiometry).
measured in the spectrum. The photocurrent stability is rather
good in the system during the monitored time.
Figure 3. Partial FT-IR spectra of 1, 5, and 1‚5 ([1]:[5] ) 2:1
After evaporation of a dichloromethane solution of the
hydrogen-bonded three-dimensional complex 1‚5 on a carbon-
coated copper grid, the superstructure of 1‚5 could be observed
in the transmission electron microscopy (TEM) image. Figure
7 shows the self-assembled balls and the size distribution
stoichiometry) in CH2Cl2.
photocurrent response is shown in Figure 6, as the irradiation
of the film was switched on and off. Importantly, the response
of on/off cycling is prompt and reproducible; four cycles are

A Novel Hydrogen-Bonded Nanostructure
J. Phys. Chem. B, Vol. 108, No. 20, 2004 6259
research.7a However, the ball-like superstructures of the 1‚5
system in dichloromethane look more uniform. And the Wu¨rth-
ner group reported the supramolecular strands of perylene
bisimide-melamine assemblies which self-organized hierarchi-
cally by means of orthogonal noncovalent interactions as given
with triple hydrogen bonding and π-π interactions in methyl-
cyclohexane.3 On the basis of this information, we presume that
the formation of the superstructures of the ball-like assemblies
of 1‚5 results from intermolecular hydrogen bonding and π-π
interactions between 1 and 5.
Conclusions
In conclusion, a novel hydrogen-bonded supramolecular
system of a [60]fullerene derivative with perylene bisimide was
synthesized and characterized. 1H NMR spectra confirmed the
existence of strong hydrogen-bonding interaction between the
[60]fullerene derivative and perylene bisimide. The ball-like
superstructure could be of importance for future studies on three-
dimensional nanomaterials applied in the field of photoelectric
devices.
Figure 6. Time dependence of the photocurrent response of the self-
assembly film. ([1]:[5] ) 2:1 stoichiometry)
histogram of the assemblies of 1 and 5. The diameters of the
balls are in the range of 30-80 nm. As the image shows, the
1‚5 system consists of spherical particles having a mean diameter
of 50 nm. It is likely that this is driven by phase transitions in
the drying process and would depend on the solvent, substrate,
and environment. The similar ball-like superstructures of self-
assemblies of organofullerene containing a 2,6-diacylaminopyr-
idine unit with a uracil derivative through three-point hydrogen
bonding in chloroform were also observed in our previous
Experimental Section
Materials and Measurements. Most of the chemical reagents
were purchased from Acros or Aldrich Corp. and were utilized
as received unless indicated otherwise. 1,6,7,12-Tetrachlorop-
erylene-3,4,9,10-tetracarboxylic acid dianhydride (2) was sup-
plied by BASF. All solvents were purified using standard
Figure 7. (a) Transmission electron micrograph of assemblies that was obtained by evaporation of a 1 × 10-5 mol/L dichloromethane solution of
the 1‚5 complex (2:1 stoichimetry) on a carbon-coated copper grid. (b) High magnification of the TEM image. (c) Size distribution histogram of
the assemblies.

6260 J. Phys. Chem. B, Vol. 108, No. 20, 2004
Liu et al.
procedures. Column chromatography was performed on silica
gel (mesh size 160-200 µm). UV/vis spectra were taken on a
Hitachi U-3010 spectrometer, and fluorescence spectra were
measured on a Hitachi F-4500 spectrofluorometer. NMR spectra
were obtained on a Bruker Avance DPS-400 (400 MHz)
spectrometer. FT-IR spectra were measured on a Bruker
EQUINOX55 spectrometer. MALDI-TOF mass spectrometric
measurements were performed on a Bruker Biflex MALDI-TOF
mass spectrometer.
overnight. The precipitate was filtered, washed neutral with
water, and dried in a vacuum at 100 °C to give a dark solid
(197 mg, 86%). The solid was purified by column chromatog-
raphy on silica (CH2Cl2/EtAc, 40:1) to give perylene bisimide
5: 1H NMR (400 MHz, CDCl3, 25 °C) δ 8.39 (s, 2H), 8.09 (s,
4H), 6.89 (d, 8H, J ) 8 Hz), 6.82 (d, 8H, J ) 8 Hz), 3.93 (t,
8H, J ) 7.2 Hz), 1.83-1.75 (m, 8H), 1.56 (s, 8H), 1.37-1.31
(m, 32H), 0.90 (m, 12H); UV/vis (CHCl3) λmax 592, 550, 458
nm; fluorescence (CHCl3) λmax 623 nm; FT-IR (KBr) ν (cm-1
)
N,N′-Dioctyl-1,6,7,12-tetrachloroperylene-3,4,9,10-tetra-
carboxylic Acid Bisimide (3). In a 100 mL single-necked flask,
1.59 g (3 mmol) of 2 was finely suspended in 50 mL of
propionic acid. Then, 2.5 mL (15 mmol) of n-octylamine was
added, and the mixture was refluxed under stirring for 24 h.
After the mixture cooled to room temperature, the precipitate
was filtered, washed neutral with water, and dried in a vacuum
at 100 °C to give the crude product as a red solid (2.03 g, 90%).
The crude product was purified by column chromatography on
3186 (N-H), 1699 (CdO), 1677 (CdO); MS (MALDI-TOF)
m/z 1270.9 (M+). Anal. Calcd for C80H90N2O12 (1270.7): C,
75.56; H, 7.13; N, 2.20. Found: C, 75.65; H, 7.30; N, 2.14.
Acknowledgment. This work was supported by the Major
State Basic Research Development Program and the National
Natural Science Foundation of China (Grants 20151002,
50372070, and 90101025).
References and Notes
1
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CDCl3, 25 °C) δ 8.69 (s, 4H), 4.23 (t, 4H, J ) 8.2 Hz), 1.75
(m, 4H), 1.45-1.26 (m, 20H), 0.90 (m, 6H); UV/vis (CHCl3)
λmax 519, 485, 426 nm; fluorescence (CHCl3) λmax 550 nm; FT-
IR (KBr) ν (cm-1) 1705 (CdO), 1666 (CdO); MS (MALDI-
TOF) m/z 750.6 (M-). Anal. Calcd for C40H38N2O4Cl4 (750.2):
C, 63.84; H, 5.09; N, 3.72. Found: C, 64.27; H, 5.22; N, 3.49.
N,N′-Dioctyl-1,6,7,12-tetra[4-(octyloxy)phenoxy]perylene-
3,4,9,10-tetracarboxylic Acid Bisimide (4). Perylene bisimide
3 (752 mg, 1 mmol), 4-(n-octyloxy)phenol (1.11 g, 5 mmol),
and K2CO3 (345 mg, 2.5 mmol) were stirred under argon in
NMP (50 mL) at 80 °C for 24 h. After being cooled to room
temperature, the reaction mixture was poured into a mixture of
10% hydrochloric acid (80 mL) and methanol (120 mL) with
stirring. The precipitate was filtered, repeatedly washed with
methanol/water (3:2), and dried in a vacuum at 100 °C.
Purification was accomplished by dissolving the crude product
in CH2Cl2 and precipitation by methanol followed by chroma-
tography on SiO2 with CH2Cl2: 1H NMR (400 MHz, CDCl3,
25 °C) δ 8.09 (s, 4H), 6.90 (d, 8H, J ) 9.7 Hz), 6.81 (d, 8H,
J ) 9.7 Hz), 3.92 (t, 8H, J ) 7.3 Hz), 2.63 (s, 4H), 2.05 (m,
8H), 1.88 (m, 4H), 1.50 (m, 12H), 1.36-1.23 (m, 48H), 0.92
(m, 18H); UV/vis (CHCl3) λmax 592, 550, 456 nm; fluorescence
(CHCl3) λmax 625 nm; FT-IR (KBr) ν (cm-1) 1697 (CdO), 1661
(CdO); MS (MALDI-TOF) m/z 1494.9 (M+). Anal. Calcd for
C96H122N2O12 (1494.9): C, 77.07; H, 8.22; N, 1.87. Found: C,
76.86; H, 8.00; N, 2.05.
1,6,7,12-Tetra[4-(octyloxy)phenoxy]perylene-3,4,9,10-tet-
racarboxylic Acid Bisimide (5). To a suspension of 4 (310
mg, 0.2 mmol) in 50 mL of 2-propanol were added 10 mL of
water and 11 g (200 mmol) of KOH. The reaction mixture was
refluxed with vigorous stirring under argon for 42 h. During
the course of the reaction, the color changed from red to green.
After being cooled to room temperature, the resulting reaction
mixture was poured into 100 mL of 10% hydrochloric acid under
stirring. A precipitate appeared and was filtered, washed neutral
with water, and dried in a vacuum at 100 °C to give a red solid
(232 mg, 87%). The red solid was not purified and was
suspended in 40 mL of propionic acid. Then, ammonium acetate
(4 g, 52 mmol) was added, and the mixture was refluxed under
stirring for 24 h. After being cooled to room temperature, the
reaction mixture was diluted with water and left to stand