Colloid chemical reaction route to the preparation of nearly monodispersed perylene nanoparticles: Size-tunable synthesis and three-dimensional self-organization

Article abstract of DOI:10.1021/ja068710d

By employing a colloid chemical reaction method we demonstrate the preparation of organic nanoparticles composed of perylene molecules (PeNPs) based on the reduction of perylene perchlorate by Br^- anions in the presence of cetyl trimethyl ammonium bromide (CTA⁺Br^-) in acetonitrile. A discrete nucleation event, followed by a slower controlled growth on the existing particles, is identified during formation of PeNPs. By changing the growth parameters, such as the monomer concentration and the method of injection, quasi-spherical PeNPs with controllable sizes from 25 to 90 nm could be obtained. The homogeneous solution phase of this method makes it capable of large-scale synthesis of PeNPs with a size distribution (<10%) that is improved by formation of a protective layer of CTA⁺ around the PeNPs. The three-dimensional, hierarchical self-organization of 25-nm PeNPs building blocks is observed to form nanobelts and square nanorods, possibly templated by the CTA⁺ lamellar micelle structures in acetonitrile. Spectroscopic results reveal two kinds of trends in the development of the optical properties of perylene as they evolve from the molecular to the bulk phase in the nanometer range. The so-called size dependence is evidenced by a switch from Y-type to E-type excimers as the size of the PeNPs increased from 25 to 90 nm. As the 25-nm PeNPs organize into nanobelts or square nanorods the oscillator strength of the Y-type excimers is relatively enhanced. That is, collective phenomena develop as the proximal particles interact in the glassy solids. Our very recent results indicate that this colloid chemical reaction method can also be applied to other organic compounds.

Full text of DOI:10.1021/ja068710d

Published on Web 05/19/2007
Colloid Chemical Reaction Route to the Preparation of Nearly
Monodispersed Perylene Nanoparticles: Size-Tunable
Synthesis and Three-Dimensional Self-Organization
Longtian Kang,†,‡ Zhechen Wang,†,‡ Zongwei Cao, Ying Ma, Hongbing Fu,* and
†,‡
†
,†
Jiannian Yao*,
†
Contribution from the Beijing National Laboratory for Molecular Sciences (BNLMS),
Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080,
People’s Republic of China and Graduate School of the Chinese Academy of Sciences,
Beijing 100039, People’s Republic of China
Received December 5, 2006; E-mail: jnyao@iccas.ac.cn; hongbing.fu@iccas.ac.cn
Abstract: By employing a colloid chemical reaction method we demonstrate the preparation of organic
nanoparticles composed of perylene molecules (PeNPs) based on the reduction of perylene perchlorate
-
+
-
by Br anions in the presence of cetyl trimethyl ammonium bromide (CTA Br ) in acetonitrile. A discrete
nucleation event, followed by a slower controlled growth on the existing particles, is identified during formation
of PeNPs. By changing the growth parameters, such as the monomer concentration and the method of
injection, quasi-spherical PeNPs with controllable sizes from 25 to 90 nm could be obtained. The
homogeneous solution phase of this method makes it capable of large-scale synthesis of PeNPs with a
size distribution (<10%) that is improved by formation of a protective layer of CTA+ around the PeNPs.
The three-dimensional, hierarchical self-organization of 25-nm PeNPs building blocks is observed to form
+
nanobelts and square nanorods, possibly templated by the CTA lamellar micelle structures in acetonitrile.
Spectroscopic results reveal two kinds of trends in the development of the optical properties of perylene
as they evolve from the molecular to the bulk phase in the nanometer range. The so-called size dependence
is evidenced by a switch from Y-type to E-type excimers as the size of the PeNPs increased from 25 to 90
nm. As the 25-nm PeNPs organize into nanobelts or square nanorods the oscillator strength of the Y-type
excimers is relatively enhanced. That is, collective phenomena develop as the proximal particles interact
in the glassy solids. Our very recent results indicate that this colloid chemical reaction method can also be
applied to other organic compounds.
Introduction
occupy the intermediate state between isolated molecules and
the bulk crystal. It has been demonstrated that not only can the
In recent years organic nanoparticles (ONPs) of low-molec-
ular-weight functional compounds have inspired growing re-
wide panel of physical properties provided by functional
compounds be fully exploited, but also these properties can also
1
-6
search efforts
due to their potential use in the fields of
3
-5
6
be modulated by the particle size
and shape. However,
optoelectronics, nonlinear optics,7 and photonics. ONPs
3
,6
8
although tailor-made molecules can generally be obtained by
organic synthesis, predicting how their properties will be
affected by the complex, nanostructured morphology is still very
†
‡
Chinese Academy of Sciences.
Graduate School of the Chinese Academy of Sciences.
(
1) (a) Kasai, H.; Nalwa, H. S.; Oikawa, H.; Okada, S.; Matsuda, H.; Minami,
N.; Kakuta, A.; Ono, K.; Mukoh, A.; Nakanishi, H. Jpn. J. Appl. Phys.
(6) (a) Balakrishnan, K.; Datar, A.; Oitker, R.; Chen, H.; Zuo, J.; Zang, L. J.
Am. Chem. Soc. 2005, 127, 10496. (b) Balakrishnan, K.; Datar, A.; Naddo,
T.; Huang, J.; Oitker, R.; Yen, M.; Zhao, J.; Zang, L. J. Am. Chem. Soc.
2006, 128, 7390. (c) Datar, A.; Balakrishnan, K.; Yang, X.; Zuo, X.; Huang,
J.; Oitker, R.; Yen, M.; Zhao, J.; Tiede, D. M.; Zang, L. J. Phys. Chem. B
2006, 110, 12327. (d) Fu, H. B.; Xiao, D. B.; Yao, J. N.; Yang, G. Q.
Angew. Chem., Int. Ed. 2003, 42, 2883. (e) Tian, Z. Y.; Chen, Y.; Yang,
W. S.; Yao, J. N.; Zhu, L. Y.; Shuai, Z. G. Angew. Chem., Int. Ed. 2004,
43, 4060.
1
992, 31, L1132. (b) Kasai, H.; Kamatani, H.; Okada, S.; Oikawa, H.;
Matsuda, H.; Nakanishi, H. Jpn. J. Appl. Phys. 1996, 35, L221. (c)
Nakanishi, H.; Oikawa, H. In Single Organic Nanoparticles; Masuhara,
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Chapter 2, pp 17-31.
(
2) Horn, D.; Rieger, J. Angew. Chem., Int. Ed. 2001, 40, 4331.
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(
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002, 124, 14410. (b) Lim, S. J.; An, B. K.; Jung, S. D.; Chung, M. A.;
Park, S. Y. Angew. Chem., Int. Ed. 2004, 43, 6346. (c) Hu, J. S.; Guo, Y.
G.; Liang, H. P.; Wan, L. J.; Jiang, L. J. Am. Chem. Soc. 2005, 127, 17090.
4) (a) Bertorelle, F.; Lavabre, D.; Fery-Forgues, S. J. Am. Chem. Soc. 2003,
(7) (a) Kim, S.; Zheng, Q. D.; He, G. S.; Bharali, D. J.; Pudavar, H. E.; Baev,
A.; Prasad, P. N. AdV. Funct. Mater. 2006, 16, 2317. (b) Oikawa, H.; Kasai,
H.; Nakanishi, H. In Anisotropic Organic Materials; Glaser, R., Kasizynski,
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2005, 17, 2070. (b) Kaneko, Y.; Shimada, S.; Fukuda, T.; Kimura, T.;
Yokoi, H.; Matsuda, H.; Onodera, H.; Kasai, H.; Okada, S.; Oikawa, H.;
Nakanishi, H. AdV. Mater. 2005, 17, 160. (c) He, C. B.; Xiao, Y.; Huang,
J. C.; Lin, T. T.; Mya, K. Y.; Zhang, X. H. J. Am. Chem. Soc. 2004, 126,
7792. (d) Wang, F.; Han, M. Y; Mya, K. Y.; Wang, Y.; Lai, Y. H. J. Am.
Chem. Soc. 2005, 127, 10350.
(
1
25, 6244. (b) Birla, L.; Bertorelle, F.; Rodrigues, F.; Badre, S.; Pansu,
R.; Fery-Forgues, S. Langmuir 2006, 22, 6256. (c) Bertorelle, F.; Rodrigues,
F.; Fery-Forgues, S. Langmuir 2006, 22, 8523.
(
5) (a) Fu, H. B.; Yao, J. N. J. Am. Chem. Soc. 2001, 123, 1434. (b) Xiao, D.
B.; Xi, L.; Yang, W. S.; Fu, H. B.; Shuai, Z. G.; Fang, Y.; Yao, J. N. J.
Am. Chem. Soc. 2003, 125, 6740. (c) Xiao, D. B.; Yang, W. S.; Yao, J. N.;
Xi, L.; Yang, X.; Shuai, Z. G. J. Am. Chem. Soc. 2004, 126, 15439. (d)
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10.1021/ja068710d CCC: $37.00 © 2007 American Chemical Society
J. AM. CHEM. SOC. 2007, 129, 7305-7312
9
7305

A R T I C L E S
Kang et al.
complicated.9,10 The electronic and optical properties of ONPs
are fundamentally different from those of inorganic nanocrystals
in both the size and the shape of the ONPs generated using this
method prevent them from acting as building blocks for further
self-organization.
(
NCs)11 due to weak intermolecular interaction forces of the
12
van der Waals type. Furthermore, the orientation between the
building units in inorganic NCs is identical since atoms can be
treated as hard spheres; in contrast, the stacking arrangement
between organic molecules plays an important role in the
properties of ONPs.13 Uncovering and mapping the structural,
electronic, and optical properties of organic compounds as they
evolve from the molecular to the bulk phase in the nanometer
range requires synthetic routes to prepare a homologous series
of monodisperse ONPs. As evidenced by inorganic NCs, sample
uniformity facilitates the organization of NCs into close-packed,
glassy, and ordered assemblies (known as NC solids) in which
new cooperative phenomena develop as the proximal NCs
interact.14 However, hindered by the methods available for the
fabrication of ONP arrays, there is an obvious lack of data
concerning the nature of the coupling between ONPs as they
assembly into close-packed solids.
Many chemical reaction syntheses for organic compounds
are conducted at room temperature in the solution phase in
which the reactant precursors are well dissolved and the target
product is generated as a precipitate. The homogeneous solution
phase makes it possible to continuously tune the supersaturation
1
4a,20
during precipitation of the target product.
We expect that
the adjustment of the reaction conditions will pave the way for
manipulating the precipitation process of the target product and
thus the resulted nanoparticles. In this study, by employing the
colloid chemical reaction method, we demonstrate for the first
time the preparation of ONPs composed of perylene molecules
-
(PeNPs) based on the reduction of perylene perchlorate by Br
21
anions in the presence of cetyl trimethyl ammonium bromide
+
-
(CTA Br ) in acetonitrile. We found that the homogeneous
solution phase of this method provides several advantages,
including the facile separation of the nucleation and growth
stages and an easier controllability of the growth parameters
by changing certain variables, such as monomer concentration
Approaches to the preparation of ONPs with well-defined
structure, however, have been limited by two facts. The first is
that ONPs require mild preparation methods because most
organic compounds are thermally fragile. The second is that
for practical use ONPs must display controllable size and shape,
even though the factors that govern these parameters are still
poorly understood (relevant to the weak van der Waals
(much higher than that in the reprecipitation method) and
method of injection. The large-scale synthesis of PeNPs ranging
from 25 to 90 nm with a polydispersity of <10% is achieved.
Furthermore, the hierarchical self-organization of 25-nm PeNP
building blocks is observed to form nanobelts and/or square
nanorods. Spectroscopic results reveal that the PeNPs and their
self-assemblies present different optical properties from those
of the monomers and bulk powder. The size dependence is
evidenced by a transition from Y-type excimers to E-type
excimers as the size of the PeNPs increases from 25 to 90 nm.
As 25-nm PeNPs organize into nanobelts or square nanorods,
development of collective phenomena is observed. Our very
recent results indicate that this colloid chemical-reaction method
can also be applied to other organic compounds.
1-6,15-19
intermolecularinteractions).Amongthefewexistingmethods
a simple and still convenient way is the so-called “reprecipitation
method”.1-6 In its most widely used variant, a dilute solution
of target compound in a water-soluble solvent (i.e., a good
solvent) is injected into vigorously stirred water as a poor
medium.1c,3-6
The good solvent disperses, and the sudden
change in the surroundings of the target compound causes its
3-6
precipitation in the form of nano- or microcrystal dispersion.
Large-scale synthesis is limited by the solubility of the target
compound in the good solvent. Moreover, the heterogeneous
environment of this method makes it difficult to precisely control
the complicated nucleation process in the initial stages and the
Results and Discussion
In our experiments, first a precursor of perylene perchlorate
2
1
4
is produced via reaction 1
subsequent fast growth. Consequently, the broad distribution
+
-
+
-
+ -
2
Pe + 2Ag ClO + I f 2Pe ClO + 2Ag I (1)
4 2 4
(
9) (a) Hu, D.; Yu, J.; Padmanaban, G.; Ramakrishnan, S.; Barbara, P. F. Nano
Lett. 2002, 2, 1121. (b) Patra, A.; Hebalkar, N.; Sreedhar, B.; Sarkar, M.;
Samanta, A.; Radhakrishnan, T. P. Small 2006, 2, 650.
where Pe is perylene. Then varying quantities of 10 mM cetyl
trimethyl ammonium bromide (CTA Br ) solution in acetoni-
trile are injected into 1 mL of 4.0 mM perylene perchlorate in
(
(
(
(
(
10) (a) McNeill, J. D.; O’Connor, D. B.; Barbara, P. F. J. Chem. Phys. 2000,
+
-
1
12, 7811. (b) Schwartz, B. J. Annu. ReV. Phys. Chem. 2003, 54, 141.
11) Alivisatos, A. P. Science 1996, 271, 933. (b) Halperin, W. P. ReV. Mod.
Phys. 1986, 58, 533.
+
-
12) Pope, M.; Swenberg, C. E. Electronic Processes in Organic Crystals;
Oxford Univ. Press: Oxford, 1982.
acetonitrile. Following reduction of Pe by Br via reaction
2
1
2
13) Silinsh, E. A. Organic Molecular Crystals: Their Electronic States;
Springer-Verlag: Berlin, 1980.
14) (a) Murray, C. B.; Kagan, C. R.; Bawendi, M. G. Annu. ReV. Mater. Sci.
+
-
+
-
2
Pe ClO + 2CTA Br f 2Pe + Br +
2
1
5
000, 30, 545. (b) Murray, C. B.; Kagan, C. R.; Bawendi, M. G. Science
4
2
995, 270, 1335. (c) Heitmann, D.; Kotthaus, J. P. Phys. Today 1993, 46,
+
-
4
6.
2CTA ClO
(2)
(
15) (a) Zhao, Y. S.; Di, C. A.; Yang, W. S.; Yu, G.; Liu, Y. Q.; Yao, J. N.
AdV. Funct. Mater. 2006, 16, 1981. (b) Zhao, L. Y.; Yang, W. S.; Luo, Y.;
Zhai, T. Y.; Zhang, G. J.; Yao, J. N. Chem. Eur. J. 2005, 11, 3773.
16) (a) Ibanez, A.; Maximov, S.; Guiu, A.; Chaillout, C.; Baldeck, P. L. AdV.
Mater. 1998, 10, 1540. (b) Sanz, N.; Gaillot, A.-C.; Usson, Y.; Baldeck,
P. L.; Ibanez, A. J. Mater. Chem. 2000, 10, 2723-2726. (c) Sanz, N.;
Wang, I.; Zaccaro, J.; Beaugnon, E.; Baldeck, P. L.; Ibanez, A. AdV. Funct.
Mater. 2002, 12, 352-358.
the newly generated perylene molecules might undergo
(
20c
nucleation and growth, giving rise to PeNPs. (Production of
1
perylene via reaction 2 has been evidenced by H NMR and
ESI-MS results, as shown in Figure S1 in the Supporting
Information. The reaction yield is nearly 100% with respect to
(
17) (a) Gong, X. C.; Milic, T.; Xu, C.; Batteas, J. D.; Drain, C. M. J. Am.
Chem. Soc. 2002, 124, 14290. (b) Balakrishnan, K.; Datar, A.; Zhang, W.;
Yang, X.; Naddo, T.; Huang, J.; Zuo, J.; Yen, M.; Moore, J. S.; Zang, L.
J. Am. Chem. Soc. 2006, 128, 6576.
+
-
the amount of CTA Br added into the system by titration of
(18) (a) Liu, H. B.; Li, Y. L.; Xiao, S. Q.; Gan, H. Y.; Jiu, T. G.; Li, H. M.;
Jiang, L.; Zhu, D. B.; Yu, D. P.; Xiang, B.; Chen, Y. F. J. Am. Chem. Soc.
(20) (a) Peng, Z. A.; Peng, X. G. J. Am. Chem. Soc. 2002, 123, 1389. (b) Peng,
Z. A.; Peng, X. G. J. Am. Chem. Soc. 2001, 123, 183. (c) LaMer, V. K.;
Dinegar, R. H. J. Am. Chem. Soc. 1950, 72, 4847.
2
003, 125, 10794. (b) Jang, J.; Oh, J. H. AdV. Mater. 2003, 15, 977.
(19) Tamaki, Y.; Asahi, T.; Masuhara, H. J. Phys. Chem. A 2002, 106, 2135.
(21) Ristagno, C. V.; Shine, H. J. J. Org. Chem. 1971, 36, 4050.
7
306 J. AM. CHEM. SOC. VOL. 129, NO. 23, 2007
9

Preparation of Perylene Nanoparticles
A R T I C L E S
Figure 1. Typical FESEM images of quasi-spherical PeNPs with a size of (A) ∼25 nm at N ) 0.3, (B) ∼60 nm at N ) 0.6 fabricated by the droplet
+
-
+
-
injection of CTA Br , and (C) ∼90 nm at about N ) 1.0 fabricated by the single injection of CTA Br . All scale bars are 200 nm.
are employed. In the case of the droplet injection method, the
size of the PeNPs increases with increasing N from 0.3 to 0.6
and then maintains a constant value of ∼ 60 nm at N g 0.6. In
the case of the single injection method, the size of the PeNPs
increases over the entire range of 0.3 e N e 1.0 and is always
larger than that obtained by droplet injection at the same N.
Moreover, the size distribution of PeNPs obtained by the single
injection method, ∼10%, is slightly larger than that obtained
by droplet injection, 5-8%.
+
-
Under conditions of N > 1.0, the amount of CTA Br is
excessive on the basis of the stoichiometric relationship in
reaction 2. The droplet injection method still produces isolated
PeNPs with a size similar to that obtained at N ) 1.0 since no
more perylene molecules can be produced for the growth of
PeNPs. In contrast, the single-injection method under conditions
of N > 1.0 produces not only isolated PeNPs but also belt-like
nanostructures (see Figure 3A, N ) 1.2). Figure 3C shows that
isolated PeNPs have a mean size of 90 nm, similar to that
obtained by the single-injection method at N ) 1.0. Figure 3B
reveals that monolayered nanobelts, i.e., nanosheets, are factually
composed of PeNPs of ∼25 nm in a line-by-line arrangement.
The width of the nanosheet is around 400 ( 50 nm, and the
length amounts to several tens or hundreds of micrometers. The
two intermediate states of Figure 3D and E, observed occasion-
ally using samples with 1.0 < N < 1.2, shield more light on
formation of nanosheets. Figure 3D shows the appearance of
nanowires of 25 nm in diameter out of a large volume of 25-
nm PeNPs, while Figure 3E shows formation of a nanosheet
by the close attachment of nanowires. These observations
suggest that 25-nm PeNPs are building blocks for the self-
organization of nanowires, which themselves can further
undergo a line-by-line self-organization to form nanosheets (see
more evidence in Figure S5). Thick nanobelts are formed with
increasing the value of N to 1.4, as shown in Figure 3F;
meanwhile, the amount of isolated 90-nm PeNPs drops con-
siderably. A layer-by-layer self-organization process can be
identified from Figure S6A in which a thinner nanosheet is
found to peel off from a thicker nanobelt. It can be seen from
Figure S6B that the match of the width of nanosheets is
important in the layer-by-layer self-organization. Under condi-
tions of N g 2.0, square nanorods are observed (Figure 3G, N
) 2.0) while the isolated 90-nm PeNPs vanish completely. The
white circle in Figure 3G marks a defect where the top and
bottom layers remain after losing the middle part, confirming
the layer-by-layer self-organization mechanism. The high-
magnification image of Figure 3H clearly indicates that nanorods
are also made up from 25-nm PeNPs, and the cross-section of
nanorods is square-shaped with sides of length ≈ 400 nm. It is
Figure 2. Sizes of PeNPs obtained by droplet (circle) and single (triangle)
injections of CTA Br at different values of N.
+
-
the remaining precursors of perylene perchlorate.) By changing
+
-
the quantity of 10 mM CTA Br solution, the molar ratio
between the reductant and perylene perchlorate, i.e., N )
+
-
+
-
N(CTA Br )/N(Pe ClO4 ), is systematically tuned. Since a
different amount of perylene molecules is produced by reaction
2
at different values of N, the size of the PeNPs can be readily
controlled. At the same value of N we found that the methods
of injection, i.e., the single and/or droplet injection methods,
+
-
also influence the size of the PeNPs. Both precursors, CTA Br
and perylene perchlorate, have good solubility in acetonitrile.
In our experiments large-scale synthesis of PeNPs ranging from
2
5 to 90 nm has been achieved. Some of their typical FESEM
images are shown in Figure 1 in which the mean sizes are 25,
0, and 90 nm. (FESEM images recorded at low magnification
6
are shown in Figures S2, S3, and S4 for PeNPs with a mean
size of 25, 60, and 90 nm, respectively.) It can be seen from
Figure 1 that the PeNPs obtained in all cases are quasi-spherical,
showing clear boundaries, and are nearly monodisperse with a
size distribution <10%.
Figure 2 summarizes the sizes of PeNPs obtained by droplet
(
circle) and single (triangle) injections at different values of N.
Three distinctive stages are identified in the range of 0 e N e
.0. (i) No particles are detectable if N < 0.2. (ii) Primary
1
particles are formed with an almost constant size of ∼25 nm
between N ) 0.2 and 0.3. (iii) Growth on the primary particles
leads to an increase in the size of the PeNPs upon increasing
the value of N from 0.3 to 1.0. Similar behaviors are observed
during the nucleation stage under conditions of N < 0.3 for
both droplet and single injection methods. However, the growth
behaviors are quite different when different injection methods
J. AM. CHEM. SOC.
9
VOL. 129, NO. 23, 2007 7307

A R T I C L E S
Kang et al.
+
-
Figure 3. Self-organization of 25-nm PeNPs observed by employing the single injection of CTA Br at N > 1.0. (A-C) N ) 1.2. (B and C) High-
magnification images showing nanosheets and isolated nanoparticles, respectively. (D and E) N ) 1.0-1.2; intermediate states observed occasionally. (F)
N ) 1.4; nanobelts. (G and H) N ) 2.0; square nanorods. (H) High-magnification image from G; the white circle in G shows a defect. See text for details.
2
2,23
the match of the width of nanosheets required by the layer-by-
layer self-organization that uniforms the nanorods into sym-
metrical square shape.
dimensional nanomaterials, including both inorganic
and
6
d
+
organic species. The hydrophobic core of CTA micelles
provides a unique environment for the nucleation of hydrophobic
materials, and the rod-like micelles serve as templates to direct
the growth of these materials. In these cases, the final structure
can be understood as a core/shell structure in which the
continuum target compounds are located in the central core
surrounded by a protective layer of CTA molecules. However,
Figure 3 presents hierarchical self-organization processes in
which the separated 25-nm PeNPs represent building blocks.
+
-
Tetrabutylammonium bromide (TBA Br ) was also em-
ployed as the reducing agent in reaction 2 for the preparation
of PeNPs. Under the conditions of N < 1.0, the behavior of the
size of PeNPs versus N is quite similar to that observed in Figure
+
+
-
2
. However, the PeNPs obtained using TBA Br are more
irregular in shape (see Figure S4) with a broad size distribution.
+
-
Moreover, aggregation of PeNPs obtained using TBA Br
becomes a serious problem (see Figure S7). Note that Br- is
+
-
Formation of micelle-like structures of CTA Br in non-
aqueous solvents, such as acetonitrile, has received far less
attention than the related phenomena in water. The conductiv-
2
1
the actual reducing agent for reaction 2 in both cases.
24
+
Therefore, the CTA molecules might form a protective layer
around the as-prepared PeNPs, serving as colloid stabilizers.
Most importantly, self-organization of PeNPs into ordered
+
-
ity of CTA Br solution versus its concentration in acetonitrile
(
22) (a) Jana, N. R.; Murphy, C. J. Chem. Commun. 2001, 617. (b) Murphy, C.
J.; Jana, N. R. AdV. Mater. 2002, 14, 80.
+
-
structures is not observed when TBA Br is used, irrespective
(
23) (a) Yu, Y. Y.; Chang, S. S.; Lee, C. L.; Wang, C. R. C. J. Phys. Chem. B
of the value of N or the method of injection employed.
1
997, 101, 6661. (b) Link, S.; Mohamed, M. B.; El-Sayed, M. A. J. Phys.
+
-
Chem. B 1999, 103, 3073.
It is known that rod-like CTA Br micelles in the aqueous
phase are widely used as templates in the synthesis of one-
(
24) Myers, D. Surfactant Science and Technology, 2nd ed.; VCH: New York,
1992.
7308 J. AM. CHEM. SOC.
9
VOL. 129, NO. 23, 2007

Preparation of Perylene Nanoparticles
A R T I C L E S
+
-
Figure 4. Changes in conductivity of CTA Br with respect to concentration in (A) acetonitrile and (B) water. The first and second critical micelle
+
-
concentrations (CMC) of CTA Br in water are observed to be about 0.9 and 20 mM (B), respectively, which are consistent with literature data. The flex
+
-
point at 2.15 mM in acetonitrile (A) suggests a transition between CTA Br monomers and micelle-like structures.
Table 1. Size of Isolated PeNPs and Self-Organization of 25-nm PeNPs under Different Experimental Conditions
+
-
a
V(CTA Br , mL)
0.12
1.07
0.3
0.24
1.94
0.6
0.40
2.85
1.0
0.48
3.24
1.2
0.56
3.59
1.4
∼60 nm
0.80
4.44
2.0
∼60 nm
+
-
b
C (CTA Br , mM)
c
N
a
droplet injection
single injection
∼25 nm
∼60 nm
∼60 nm
∼60 nm
a
∼25 nm
∼76 nm
∼90 nm
self-organization of
25-nm PeNPs
a
+
-
b
+
-
The different volume of 10 mM CTA Br was added into 1 mL of 4 mM perylene perchlorate in acetonitrile. Final concentration of CTA Br in the
c
+
-
+
-
colloidal suspensions of PeNPs, C ) 10 mM × V mL/(1.0 mL + V mL) N ) N(CTA Br )/N(Pe ClO4 ) ) (10 mM × V mL)/(1 mM × 4 mL).
Figure 5. Schematic illustration representing formation of quasi-spherical PeNPs (upper path including stage I and stage II) and hierarchical self-organization
of 25-nm PeNPs into nanobelts (lower path including Stages I, III, and IV): stage I, Nucleation; stage II, Growth; stages III and IV, 1D to 3D organization.
See text for details.
reveals a flex point at 2.15 mM (see Figure 4A). A parallel
experiment was also carried out in the aqueous phase. The
observed flex points at 0.9 and 20 mM correspond well to the
On the basis of the above observations, we summarized the
experimental results under different experimental conditions in
Table 1 and proposed a possible mechanism in Figure 5 for
formation of PeNPs (upper path) as well as self-organization
of 25-nm PeNPs (lower path). Under conditions of N < 0.2,
the concentration of perylene molecules produced through
reaction 2 is not enough to initiate nucleation. Between N )
0.2 and 0.3, however, it reaches the nucleation threshold. A
nucleation burst generates primary PeNPs with a mean size of
+
-
first and second critical micelle concentrations of CTA Br in
water (see Figure 4B).25 Dynamic light scattering (DLS)
+
-
measurements of 3.0 mM CTA Br in water present a single
size distribution centered at 7.9 nm, indicating formation of
2
5a
spherical micelles in the aqueous phase.
However, DLS
+
-
measurements of 3.0 mM CTA Br in acetonitrile yield
multiple distributions varying randomly from several hundreds
to several thousands of nanometers. It is reasonable that CTA
2
0c
∼25 nm. This is a diffusion/reaction/nucleation-controlled
+
process (stage I in Figure 5) and so is not influenced by the
+
molecules may form complicated aggregates in acetonitrile, for
various methods of injection. Once primary PeNPs form, CTA
24
example, rod-like or lamellar micelles, if the concentration
molecules can attach to them through hydrophobic interactions
+
+
of CTA is above 2.15 mM.
between the alkyl chains of CTA and perylene, forming a
protective layer (see left second picture in Figure 5). Note that
the primary PeNPs and perylene cations remaining in the system
are separated from each other because of electrostatic repulsive
(
25) (a) Imae, T.; Kamiya, R.; Ikeda, S. J. Colloid Interface Sci. 1985, 108,
15. (b) Shikata, T.; Hirata, H.; Kotaka, T. Langmuir 1988, 4, 354. (c)
Lianos, P.; Lang, J.; Strazielle, C.; Zana, R. J. Phys. Chem. 1982, 86, 1019.
2
J. AM. CHEM. SOC.
9
VOL. 129, NO. 23, 2007 7309

A R T I C L E S
Kang et al.
+
-
interactions. By adding further CTA Br over N ) 0.3, more
perylene molecules are released by reaction 2 slowly and
smoothly into the solution phase. As long as the consumption
of feedstock by the growing PeNPs is not exceeded by the rate
of perylene production, no new nuclei form. In other words,
stage I of the nucleation process is separated from stage II of
the growth process during formation of PeNPs (see Figure 5).
The amount of perylene produced via reaction 2 increases with
increasing N in the range of 0.3 e N e 1.0; thus, the size of
the PeNPs can be readily controlled. Since the instant concen-
tration of perylene (supersaturation) is high when the single-
injection method is employed, the growth rate of the primary
5-nm PeNPs is fast.1
4a,20c
This is why both the size and the
2
size distribution of PeNPs obtained by the single-injection
method are larger than those obtained by the droplet injection
method at the same value of N. As mentioned above, the size
of the PeNPs obtained by the droplet injection method maintains
a constant value of 60 nm above N ) 0.6 at which the
+
concentration of CTA is close to 2.15 mM, as shown in Table
1
. Therefore, this might be due to formation of aggregate
+
structures of CTA in the system. In any event, it is the
separation between the nucleation and growth stages that
improves the monodispersity of as-prepared PeNPs < 10%.
Under the conditions of N > 1.0, 60-nm PeNPs are already
formed in the case of the droplet injection method. However,
the situation is entirely different when the single-injection
method is employed (stages III and IV in Figure 5). (i) A large
amount of primary 25-nm PeNPs can be generated instantly
prior to the growth process. This provides possible driving forces
(interfacial energy) for self-organization of the 25-nm PeNPs
due to the tendency of the system to try to minimize the free
energy.26 (ii) As above-mentioned, CTA molecules can form
a protective layer around PeNPs. Under high concentration of
+
Figure 6. Absorption (A) and emission (B) spectra of samples prepared
+
-
by the single injection of CTA Br at different values of N: (a) spherical
PeNPs (25 nm) at N ) 0.3, (b) spherical PeNPs (90 nm) at N ) 1.0, (c)
nanobelts at N ) 1.4, and (d) square nanorods at N ) 2.0. Spectra m and
2
5-nm PeNPs in the colloidal suspension, the surface-bound
+
CTA molecules can also assist in drawing the PeNPs closer
to share a common layer of counterions or through the inner
digitation of CATB tails from neighboring nanoparticles. (iii)
-5
p are recorded for monomers in 1.0 × 10 M perylene/acetonitrile solution
and bulk powder, respectively.
2
7
+
present different optical properties from those of the monomers
and bulk powder. Figure 6A is the diffuse reflectance absorption
spectra of nanoparticle samples that have been filtered on the
surface of an alumina membrane. The appearance of a new peak
in spectra a-d around 500 nm is ascribed to aggregate states
Since the concentration of CTA in the samples with N > 1.0
is greater than 2.15 mM (see Table 1), the rod-like or lamellar
micelle structures in the stock solution will exist when the single-
injection method is employed. The rod-like micelles can induce
6
d
self-organization of 25-nm primary PeNPs into nanowires.
Furthermore, the lamellar micelles already present in solution
1
b
and an indication of formation of nanoparticles. Meanwhile,
the absorption bands between 350 and 450 nm corresponding
to the molecular states in spectra a-d is slightly red-shifted
from that in the monomer spectrum of m.
-
- 28
or induced by replacement of the Br counter ions by ClO4
serve as templates for self-organization of nanowires into
nanobelts. Growth and self-organization of 25-nm PeNPs are
competitive processes in the range of 1.0 < N < 2.0. Under
the conditions of N g 2.0, the latter process becomes the
dominant pathway and only square nanorods are observed.
The spectroscopic studies, when correlated with the FESEM
observations, further clarify formation of spherical PeNPs with
different sizes as well as confirm the hierarchical self-organiza-
tion of 25-nm PeNPs into nanobelts and square nanorods. In
Figure 6, spectra m and p correspond to monomers in dilute
solution and bulk powder, respectively. It can be seen from
Figure 6 that PeNPs and their self-assemblies (colored spectra)
The emission spectrum a in Figure 6B observed for 25-nm
PeNPs is dominated by transitions from the molecular states
between 375 and 525 nm together with weak emissions at 535,
5
70, and 615 nm, which are attributed to the aggregate states.
The emission spectrum p of the bulk powder presents peaks at
70 and 595 nm which are typical emissions associated with
the so-called E-type excimer, i.e., a single-center sandwich or
5
29-31
card-packed-type excimer.
Therefore, the emission features
of 25-nm PeNPs at 570 and 615 nm are assigned to E-type
excimers, while that at 535 nm is assigned to a Y-type excimer,
(
29) Tanaka, J. Bull. Chem. Soc. Jpn. 1963, 36, 1237.
(
26) Cross, M. C.; Hohenberg, P. C. ReV. Mod. Phys. 1993, 65, 851.
27) (a) Wang, Z. L. J. Phys. Chem. B 2000, 104, 1153. (b) Sau, T. K.; Murphy,
C. J. Langmuir 2005, 21, 2923.
(30) Weiss, D.; Kietzmann, R.; Mahrt, J.; Tufts, B.; Storck, W.; Willing, F. J.
Phys. Chem. 1992, 96, 5320.
(
(31) (a) Akimoto, S.; Ohmori, A.; Yamazaki, I. J. Phys. Chem. B 1997, 101,
3753. (b) Liu, J. S.; Wang, L.; Gao, F.; Li, Y. X.; Wei, Y. Anal. Bioanal.
Chem. 2003, 377, 346.
(28) Zhang, X. T.; Zhang, J.; Liu, Z. F.; Robinson, C. Chem. Commun. 2004,
1
6, 1852.
7310 J. AM. CHEM. SOC.
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VOL. 129, NO. 23, 2007

Preparation of Perylene Nanoparticles
A R T I C L E S
i.e., a two-center or partial overlapping excimer.32 Remarkably,
Figure 6B elucidates two different kinds of trends in the
development of the emission properties if the 25-nm PeNPs are
considered as a starting point. (i) As the size of the PeNPs
increases from 25 to 90 nm, the emission from the aggregate
states at longer wavelengths becomes dominant and shifts from
a Y-type excimer at 535 nm (spectrum a) to a E-type excimer
at 570 nm (spectrum b). Perylene microcrystals in the range
from 300 nm to 1 µm, prepared by the reprecipitation method,
have been reported to show size-dependent optical proper-
self-organization of PeNPs with size ∼25 nm is observed to
form nanobelts and square nanorods, possibly templated by the
+
CTA lamellar micelle structures in acetonitrile. Spectroscopic
results reveal two kinds of trends in the development of the
optical properties of perylene as they evolve from the molecular
to the bulk phase in the nanometer range. The size dependence
is characterized by a switch from formation of Y-type excimers
to E-type excimers as the size of the PeNPs increases from 25
to 90 nm. As the 25-nm PeNPs organize into nanobelts or square
nanorods, the oscillator strength of the Y-type excimers is
relatively enhanced. That is, collective phenomena develop as
proximal particles interact in the glassy solids. Our results
suggest that the colloidal chemical reaction method and
subsequent self-organization might be useful in the fabrication
of highly ordered organic nanomaterials.
3
3,34
ties.
The particle size dependence of the emission maxima
1b,33,34
is explained in terms of lattice softening,
which makes
the intermolecular interactions weaker and modifies the energy
level of the excimer state (only E-type in ref 33). Our results
add new data for the range below 100 nm. The quasi-spherical
shape of the PeNPs (<100 nm) suggests that these particles
are amorphous. Lattice softening is therefore no longer an
appropriate term. However, the intermolecular interactions might
still decrease with decreasing particle size since the surface-
to-volume ratio increases significantly in this range. The loose
intermolecular environment allows coexistence of both E-type
and Y-type excimers in PeNPs, the percentages of which are
dependent on the particle size. (ii) It can also be seen from
Figure 6 that the absorption at 500 nm (Figure 6A) and the
luminescence at 535 nm (Figure 6B) in the self-organization
samples (spectra c and d) become stronger than those of the
Experimental Section
Materials. Compounds perylene and silver perchlorate were pur-
chased from Aldrich chemical Co. Iodine (A.R.), cetyl trimethyl
+
-
ammonium bromide (CTA Br , A.R.), and tetrabutylammonium
+
-
bromide (TBA Br ) were obtained from Beijing Chemical Co., China.
Solvents dichloromethane (HPLC grade) and anhydrous acetonitrile
(water < 0.001%) were purchased from Tianjin Chemical Co. and
Aldrich, respectively. Ultrapure water with a resistivity of 18.2 MΩ
was produced using a Milli-Q apparatus (Millipore). Alumina mem-
branes with a pore size of 20 nm and polytetrafluoroethylene filters
(PTFE, Puradisc 25 TF, 0.1 µm) were bought from Whatman
2
5-nm PeNP building blocks (spectrum a), a result which cannot
International Ltd.
1b,33,34
be explained by the size-dependence theory.
As shown
Preparation and Analysis of PeNPs. (A) Preparation of Perylene
Perchlorate.21 A solution of 1 mmol of dry silver perchlorate in a
minimum amount of anhydrous acetonitrile was added into a 100 mL
solution of 10 mM perylene in anhydrous dichloromethane with stirring.
To this mixture was added a solution of 0.5 mmol of iodine in a
minimum amount of anhydrous dichloromethane. A dark precipitate
formed immediately. After stirring for 15 min, the mixture was
separated by centrifuging at 12 000 rpm. Relying on the difference in
solubility between silver iodide and perylene perchlorate in acetonitrile,
perylene perchlorate is separated from the admixture and dried under
vacuum at room temperature.
in Figure 3, the nanobelts and square nanorods are glassy solids
formed by the building blocks of 25-nm PeNPs. The width of
these nanobelts and square nanorods is 400 nm, while their
length amounts to several micrometers. Though the size of the
square nanorods is much larger than that of the 90-nm PeNPs,
the emission maxima of the former (spectrum d) at 535 nm is
still attributed to the Y-type excimers, different from the
emission maxima of the latter at 570 nm attributed to the E-type
excimers (spectrum b). The enhancement of the oscillator
strength for Y-type excimers upon assembling 25-nm PeNPs
into glassy solids is due to the fact that collective phenomena
develop as proximal 25-nm PeNPs interact. This opens up the
possibilities of fabricating solid-state materials with novel
physical properties.
+
-
(
B) Preparation of PeNPs. Varying quantities of 10 mM CTA Br
+
-
or TBA Br solution in anhydrous acetonitrile were added into 1 mL
of 4 mM perylene perchlorate in anhydrous acetonitrile under vigorous
stirring. After injection, the aubergine solution gradually turned yellow,
and the colloidal suspension of PeNPs was obtained. The nanoparticle
samples collected on the surface of an alumina membrane were dried
under vacuum, washed twice with ultrapure water, and finally dried
again under vacuum for further analysis. In our experiment the size of
PeNPs was tuned by both the methods of injection, i.e., quick single
injection or droplet addition (25 µL/drop, 1 drop/30 s), and the molar
ratio of the reducing agent to the perylene perchlorate, i.e., N )
Conclusion
In summary, we demonstrate that the colloid chemical method
in the solution phase can be applied to the preparation of
perylene nanoparticles. The homogeneous solution phase of this
method provides several advantages, including facile separation
of the nucleation and growth stages and an easier controllability
of the growth parameters, such as the monomer concentration
and method of injection. The large-scale synthesis of PeNPs
ranging from 25 to 90 nm is achieved with a size distribution
+
-
+
-
4
). Experimental results under different ex-
N(CTA Br )/N(Pe ClO
perimental conditions are summarized in Table 1.
C) Analysis. First, the sample on the alumina membrane was
(
1
analyzed by H NMR (400 MHz, Bruker ARX 400 Spectrometer) and
ESI-MS (LC-MS 1020), and the details can be found in the Supporting
Information (see Figure S1). The morphology and size of the sample
were examined by field emission scanning electron microscopy
(
<10%) that is improved by formation of a protective layer of
+
CTA around the PeNPs. The three-dimensional hierarchical
(FESEM, Hitachi S-4300). The optical properties of the sample were
(
(
(
32) Xie, R. M.; Xiao, D. B.; Fu, H. B.; Ji, X. H.; Yang, W. S.; Yao, J. N. New
investigated by steady-state fluorescent (Hitachi F-4500) and diffuse
reflectance UV-vis absorption spectroscopies (Lambda 35 1.27
spectrometer), respectively. All samples remain stable after being kept
at room temperature in air for several months according to a comparison
the optical properties before and after. The quantum yield of perylene
nanoparticles, which were redispersed into ultrapure water, was
J. Chem. 2001, 25, 1362.
33) Oikawa, H.; Mitsui, T.; Onodera, T.; Kasai, H.; Nakanishi, H.; Sekiguchi,
T. Jpn. J. Appl. Phys. 2003, 42, L111.
34) (a) Kasai, H.; Kamatani, H.; Yoshikawa, Y.; Okada, S.; Oikawa, H.;
Watanabe, A.; Itoh, O.; Nakanishi, H. Chem. Lett. 1997, 26 (9), 1181. (b)
Latterini, L.; Roscini, C.; Carlotti, B.; Aloisi, G. G.; Elisei, F. Phys. Stat.
Sol. 2006, 203, 1470.
J. AM. CHEM. SOC.
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A R T I C L E S
Kang et al.
measured to be 0.09 at 298 K using the anthracene in ethanol as the
standard (quantum yield, 0.27).34b,35 (The mean deviation in the
measurement of the quantum yield is 20%, largely owing to the Mie
scattering of the colloidal suspensions.)
Fund for Fundamental Key Project 973 (2006CB806200). The
authors thank Prof. Y. L. Wang in the same institute for her
assistance in the measurement of CTA Br conductance.
+
-
Supporting Information Available: 1H NMR (400 MHz) and
EI-MS spectra of perylene from nanoparticle samples; FESEM
images of perylene nanoparticles and their self-assemblies
formed under different experimental conditions. This material
is available free of charge via the Internet at http://pubs.acs.org.
Acknowledgment. This work was supported by the National
Natural Science Foundation of China (Nos. 90301010, 20373077,
0471062, 50573084, 90606004), the Chinese Academy of
Sciences (“100 Talents” Program), and the National Research
2
(
35) Eaton, D. F. Luminescence spectroscopy. In Handbook of Organic
Photochemistry; Scaiano, J. C., Ed.; CRC Press; Boca Raton, 1989; Vol.
1
.
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