Fabrication of nanocrystals from diolefin derivatives and their solid-state photoreaction behavior

Article abstract of DOI:10.1021/cg900511z

Nanocrystals of seven p-phenylenediacrylates, i.e., dimethyl (la), didecyl (lb), diundecyl (1c), ditetradecyl (1d), dipentadecyl (1e), dioctadecyl (1f), and dicholesteroyl (1g) derivatives, and 2,5-distyrylpyrazine (2) were fabricated by the reprecipitation method and their photochemical reaction behaviors were investigated in comparison to those of bulk crystals. The bulk crystals of 1a- 1c and 2 were found to be photoreactive, whereas those of 1d-1g were less photoreactive. In contrast, all of the nanocrystals of 1a-1g and 2 showed high photoreactivity. Nanocrystals of la and 2 were demonstrated to have the same packing as the corresponding polymerizable bulk crystals, and they gave the corresponding polymers by photoirradiation. The polymer crystal structures in their nanocrystals were confirmed to be the same as those in bulk crystals by X-ray and electron diffraction analyses. Their single-crystal-to-single-crystal transformation was established by their nanocrystallization. On the other hand, other nanocrystals (1b-1g) were found to have different packings compared with the corresponding bulk crystals. After photoirradiation, their crystallinity was degraded to form amorphous products.

Full text of DOI:10.1021/cg900511z

DOI: 10.1021/cg900511z
Fabrication of Nanocrystals from Diolefin Derivatives and Their
Solid-State Photoreaction Behavior
2010, Vol. 10
510–517
Hirohiko Miura,† Shu Takahashi,† Hitoshi Kasai,† Shuji Okada,*,‡ Kiyoshi Yase,§
Hidetoshi Oikawa,† and Hachiro Nakanishi†
†Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University,
Sendai 980-8577, Japan, ‡Graduate School of Science and Engineering, Yamagata University,
Yonezawa 992-8510, Japan, and §National Institute of Advanced Industrial Science and Technology
(AIST), Tsukuba 305-8565, Japan
Received May 11, 2009; Revised Manuscript Received November 17, 2009
ABSTRACT: Nanocrystals of seven p-phenylenediacrylates, i.e., dimethyl (1a), didecyl (1b), diundecyl (1c), ditetradecyl (1d),
dipentadecyl (1e), dioctadecyl (1f), and dicholesteroyl (1g) derivatives, and 2,5-distyrylpyrazine (2) were fabricated by the re-
precipitation method and their photochemical reaction behaviors were investigated in comparison to those of bulk crystals. The
bulk crystals of 1a-1c and 2 were found to be photoreactive, whereas those of 1d-1g were less photoreactive. In contrast, all of
the nanocrystals of 1a-1g and 2 showed high photoreactivity. Nanocrystals of 1a and 2 were demonstrated to have the same
packing as the corresponding polymerizable bulk crystals, and they gave the corresponding polymers by photoirradiation. The
polymer crystal structures in their nanocrystals were confirmed to be the same as those in bulk crystals by X-ray and electron
diffraction analyses. Their single-crystal-to-single-crystal transformation was established by their nanocrystallization. On the
other hand, other nanocrystals (1b-1g) were found to have different packings compared with the corresponding bulk crystals.
After photoirradiation, their crystallinity was degraded to form amorphous products.
1. Introduction
and 2, were found to transform from a monomer single crystal
to a polymer single crystal, while their bulk crystals break into
crystalline fragments. The results strongly support that poly-
mers with molecular weight depending on the size of start-
ing monomer nanocrystals are obtained even from diolefin
monomers.
In the present study, in order to make clear the topochemi-
cal polymerization of a series of diolefin compounds in
nanocrystals, diolefin compounds modified by long-alkyl
chains or bulky cholesterolyl groups (1b-1g in Scheme 1) as
well as 1a and 2 were investigated focusing on the fabrication
of nanocrystals andtheir photoreaction behaviorsin compari-
son to the corresponding bulk crystals.
Topochemical photopolymerization of 2,5-distyrylpyra-
zine (2 in Scheme 1) was first reported in 1967.1 The space
group of crystal 2 (Pbca) was found to be retained during
the [2 þ2] cycloaddition polymerization from the crystallo-
graphic study.2 The result was the first evidence of a poly-
merization reaction in the crystal lattice. After this report,
the [2 þ2] topochemical reaction was investigated on a large
number of diolefin compounds in detail, to afford a variety of
products such as highly crystalline linear polymers, stereo-
specific polymers having an alternating zigzag or linear main-
chain structure, copolymers from the mixed crystals, optically
active compounds, cyclophanes, and so on.3 On the other
hand, several diacetylene4 and (Z,Z)-muconic acid deriva-
tives5 are known to show the other type of topochemical
polymerization, i.e., single-crystal-to-single-crystal transfor-
mation even in bulk crystals via chain polymerization to
afford the corresponding polymer single crystals. Especially
in polydiacetylene, its molecular-weight control was quali-
tatively demonstrated in its size-controlled nanocrystals.6
Molecular-weight difference was also found in ethyl (Z,Z)-
muconate crystals prepared in different sizes.7 Namely,
molecular-weight control of polymers can be achieved by the
solid-state polymerization of size-controlled monomer nano-
crystals. In contrast to these two series of monomers, different
characteristics of diolefin derivatives were observed, i.e., the
bulk crystals of diolefin derivatives are broken into fragments
from a monomer single crystal during the [2 þ 2] photopoly-
merization because of the strain accumulation.8 In our pre-
vious communication,9 however, nanocrystals of two diolefin
derivatives, dimethyl p-phenylenediacrylate (1a in Scheme 1)
2. Experimental Section
Measurements. Melting points of the monomers were determined
using a Yanaco MP-500. 1H NMR spectra of the monomers were
measured in CDCl3 using a Jeol Lambda 400 spectrometer. FT-IR
spectra were recorded on a Shimadzu FTIR-8100 M spectrometer.
UV-visible spectra were obtained for nanocrystal water disper-
sions using a Jasco V-570 spectrometer. The size of nanocrystals in
water dispersion was evaluated by the homodyne spectroscopy of
the dynamic light scattering (DLS) method using an Otsuka Elec-
tronics DLS-7000 with a He-Ne laser source (632.8 nm). The size
and shape of nanocrystals were verified using a Jeol JSF-6700F
scanning electron microscope (SEM). For SEM observation, the
nanocrystals were collected by filtration using membrane filters
(Millipore VM, pore size 50 nm). X-ray powder diffraction analyses
were carried out using a Mac Science MX18XHF22-SRA X-ray
diffractometer with a Cu KR source. The shape of bulk crystals was
observed under an Olympus BHS-751-P polarizing microscope.
Electron diffraction study of nanocrystals was performed by using
a Hitachi H-9000NA transmission electron microscope with an
accelerating voltage of 300 kV. The nanocrystal-dispersed solution
was dropped onto a silver-coated porous plastic film on a copper
mesh and then dried. The silver film was used as a standard in
electron diffraction patterns.
*Corresponding author. Phone and fax: þ81-238-26-3741. E-mail:
okadas@yz.yamagata-u.ac.jp.
r
pubs.acs.org/crystal
Published on Web 12/22/2009
2009 American Chemical Society

Article
Crystal Growth & Design, Vol. 10, No. 2, 2010 511
Scheme 1. Preparative Routes of the Diolefin Monomers
Preparation of Diolefin Derivatives. Preparative routes of the
(m, 28H, -(CH2)7-C2H5), 1.70 (m, 4H, -CH2-CH3), 4.20 (t, 4H,
J = 6.8 Hz, -O-CH2-C9H19), 6.47 (d, 2H, J = 16.0 Hz, olefin), 7.54
(s, 4H, phenylene), 7.66 (d, 2H, J = 16.0 Hz, olefin) ppm. Anal.
Calcd for C32H50O4: C, 77.06%; H, 10.10%. Found: C, 76.94%; H,
10.24%.
diolefin monomers are shown in Scheme 1. Among the compounds
synthesized, long-alkyl-chain diesters 1c and 1e and cholesterolyl
diester 1g were newly prepared in the present work.
p-Phenylenediacrylic Acid. p-Phenylenediacrylic acid was pre-
pared by condensation of terephthalaldehyde with malonic acid in
the presence of pyridine and a few drops of piperidine at 100 °C until
the starting materials disappeared on TLC (yield 86%). mp>
300 °C (lit. mp 360 °C10); 1H NMR (400 MHz, δ in DMSO-d6)
6.58 (d, 2H, J = 15.8 Hz, olefin), 7.58 (d, 2H, J = 15.8 Hz, olefin),
7.71 (s, 4H, phenylene) ppm.
p-Phenylenediacryloyl Dichloride. p-Phenylenediacrylic acid was
refluxed with thionyl chloride until the starting material dis-
appeared on TLC, affording p-phenylenediacryloyl chloride (yield
98%). Resulting p-phenylenediacryloyl dichloride was provided for
subsequent esterification without further purification. 1H NMR
(400 MHz, δ in CDCl3) 6.72 (d, 2H, J = 15.6 Hz, olefin), 7.65 (s, 4H,
phenylene), 7.83 (d, 2H, J = 15.6 Hz, olefin) ppm.
Dimethyl p-Phenylenediacrylate (1a). p-Phenylenediacryloyl
dichloride (3.00 g, 11.8 mmol) in chloroform (20 mL) was refluxed
with methanol (5 mL, 60.2 mmol) until the starting material
disappeared on TLC. The reaction mixture was diluted by chloro-
form and washed with water. Then, the chloroform solution was
dried over anhydrous MgSO4 and filtered. Solvent in the filtrate was
evaporated, and the residue was purified by column chromato-
graphy (Wako Gel, C-300) eluted by chloroform. The desired
fraction was recrystallized from a mixture of methanol and chloro-
form to give 2.3 g (9.34 mmol) of dimethyl p-phenylenediacrylate
(yield 79%). mp 170 °C (lit. mp 171 °C11); IR (KBr) 1707,
1628 cm-1; 1H NMR (400 MHz, δ in CDCl3) 3.82 (s, 6H, methyl),
6.48 (d, 2H, J =16.1 Hz, olefin), 7.54 (s, 4H, phenylene), 7.68
(d, 2H, J =16.1 Hz, olefin) ppm.
Other p-phenylenediacrylates were prepared by similar proce-
dure with a corresponding alcohol or cholesterol.
Diundecyl p-Phenylenediacrylate (1c). Yield 58% recrystallized
from hexane; mp 72 °C; IR (KBr) 1703, 1640 cm-1 1H NMR
;
(400 MHz, δ in CDCl3) 0.88 (t, 6H, J = 7.1 Hz, methyl), 1.27 (m,
32H, -(CH2)8-C2H5), 1.70 (m, 4H, -CH2-CH3), 4.20 (t, 4H, J = 6.8
Hz, -O-CH2-C10H21), 6.47 (d, 2H, J = 16.0 Hz, olefin), 7.54 (s, 4H,
phenylene), 7.66 (d, 2H, J = 16.0 Hz, olefin) ppm. Anal. Calcd for
C
34H54O4: C, 77.52%; H, 10.33%. Found: C, 77.35%; H, 10.47%.
Ditetradecyl p-Phenylenediacrylate (1d). Yield 71% recrystallized
from hexane; mp 77 °C (lit. mp 84 °C13); IR (KBr) 1711, 1639 cm-1
;
1H NMR (400 MHz, δ in CDCl3) 0.88 (t, 6H, J = 7.1 Hz, methyl),
1.26 (m, 44H, -(CH2)11-C2H5), 1.70 (m, 4H, -CH2-CH3), 4.21 (t, 4H,
J = 6.8 Hz, -O-CH2-C13H27), 6.47 (d, 2H, J = 16.0 Hz, olefin), 7.54
(s, 4H, phenylene), 7.66 (d, 2H, J = 16.0 Hz, olefin) ppm. Anal.
Calcd for C40H66O4: C, 78.64%; H, 10.89%. Found: C, 78.61%; H,
10.74%.
Dipentadecyl p-Phenylenediacrylate (1e). Yield 61% recrystal-
lized from a mixture of hexane and chloroform; Mp 82 °C; IR (KBr)
1701, 1641 cm-1; 1H NMR (400 MHz, δ in CDCl3) 0.88 (t, 6H, J =
7.1 Hz, methyl), 1.27 (m, 48H, -(CH2)12-C2H5), 1.70 (m, 4H, -CH2-
CH3), 4.20 (t, 4H, J = 6.8 Hz, -O-CH2-C14H29), 6.47 (d, 2H, J =
16.0 Hz, olefin), 7.54 (s, 4H, phenylene), 7.66 (d, 2H, J = 16.0 Hz,
olefin) ppm. Anal. Calcd for C42H70O4: C, 78.94%; H, 11.04%.
Found: C, 78.79%; H, 11.35%.
Dioctadecyl p-Phenylenediacrylate (1f). Yield 71% recrystallized
from a mixture of hexane and chloroform; mp 88 °C (lit. mp 85-87
°C13b); IR (KBr) 1711, 1639 cm-1; 1H NMR (400 MHz, δ in CDCl3)
0.88 (t, 6H, J = 7.1 Hz, methyl), 1.25 (m, 60H, -(CH2)15-C2H5), 1.70
(m, 4H, -CH2-CH3), 4.20 (t, 4H, J = 6.8 Hz, -O-CH2-C17H35), 6.47
(d, 2H, J = 16.0 Hz, olefin), 7.54 (s, 4H, phenylene), 7.66 (d, 2H,
J = 16.0 Hz, olefin) ppm. Anal. Calcd for C48H82O4: C, 79.72%; H,
11.43%. Found: C, 79.41%; H, 11.59%.
Didecyl p-Phenylenediacrylate (1b). Reaction of p-phenylenedia-
cryloyl dichloride (2.00 g, 7.80 mmol) with 1-decanol (3.40 mL, 18.7
mmol) was carried out in toluene (15 mL) at 80 °C until the starting
material disappeared on TLC. After evaporation of the solvent, the
residue was dissolved into chloroform and washed with water.
Then, the chloroform solution was dried over anhydrous MgSO4
and filtered. Solvent in the filtrate was evaporated and the residue
was purified by column chromatography (Wako Gel, C-300) eluted
by chloroform. The desired fraction was recrystallized from hexane
to afford 1.84 g (3.69 mmol) of didecyl p-phenylenediacrylate (yield
Dicholesteroyl p-Phenylenediacrylate (1g). Yield 57% recrystal-
lized from a mixture of hexane and chloroform; mp 137 °C; IR
(KBr) 1714, 1634 cm-1 1H NMR (400 MHz, δ in CDCl3) 0.69
;
(s,6H), 0.86-2.04 (m, 66H), 2.40 (d, 4H, J = 7.8 Hz), 4.74 (m, 2H),
5.40 (d, 2H, J = 3.7 Hz), 6.45 (d, 2H, J = 16.1 Hz, olefin), 7.53 (s,
4H, phenylene), 7.65 (d, 2H, J = 16.1 Hz, olefin) ppm. Anal. Calcd
1
62%). mp 74 °C (lit. mp 64 °C12); IR (KBr) 1710, 1637 cm-1; H
NMR (400 MHz, δ in CDCl3) 0.88 (t, 6H, J = 7.1 Hz, methyl), 1.27

512 Crystal Growth & Design, Vol. 10, No. 2, 2010
Miura et al.
Figure 1. SEM images of 1d nanocrystals: (a) injection of 5 mmol/L solution without microwave irradiation, (b) injection of 5 mmol/L solution
followed by microwave irradiation, (c) injection of 2 mmol/L solution followed by microwave irradiation, and (d) injection of 20 mmol/L
solution followed by microwave.
for C66H98O4: C, 82.96%; H, 10.34%. Found: C, 82.84%; H,
10.58%.
2,5-Distyrylpyrazine (2). 2,5-Distyrylpyrazine was successfully
prepared by the condensation reaction of 2,5-dimethylpyrazine with
benzaldehyde in benzoic anhydride under refluxing. Recrystalliza-
tion was performed from xylene; mp 223 °C (lit. mp 219 °C14).
Fabrication of Nanocrystals. A typical reprecipitation proce-
dure15 was as follows: A solution (200 μL) of a diolefin compound
in a good solvent such as tetrahydrofuran (THF) prepared to
5.0 mmol/L was rapidly injected by a microsyringe into 10 mL of a
poor solvent such as pure water stirred vigorously at room tempera-
turetogivea dispersionofnanocrystals. Amountofinjection solution
and poor solvent was not changed even when concentration of
injection solution was varied. In this procedure, several pairs of good
and poor solvents were investigated. Since some of the nanocrystal
dispersions prepared were not stable enough to maintain their
dispersion state, microwave irradiation (2.45 GHz, 50 W, 7 min)16
was also performed just after reprecipitation.
Polymerization by UV Irradiation. Bulk Crystals. Photoreacti-
vity in the bulk crystalline state was investigated for KBr pellets
containing the crystals of 1a-1f and 2. The light source was a 500 W
ultra-high-pressure Hg lamp (Ushio SX-UI 500HP), and the light
was passed through a cold mirror unit (Ushio MR-5090) and a filter
(Ushio U-340) for irradiation. During the photoirradiation, IR
spectra of the pellets were monitored. For the photoreaction of
bulk crystals on a preparative scale, finely powdered crystals were
dispersed in pure water containing a few drops of sodium dodecyl-
Figure 2. SEM images of diolefin nanocrystals: (a) 1b, (b) 1c, (c) 1e,
(d) 1f, (e) 1g, and (f) 2. For compounds except 1g, 5 mmol/L solution
was injected. For 1g, 2.5 mmol/L solution was injected. Microwaves
were irradiated after solution injection except for 2.
sulfonate solution by rigorous stirring, or they were just placed on a
nanocrystal coagulation occurred even in water dispersions
glass plate. Irradiation was performed for 1-30 h at 0 °C using the
upon long-term storage. On the other hand, when micro-
same light as above.
waves was irradiated after reprecipitation, the average crys-
tal size was not changed at around 200 nm, but the
coagulation was markedly suppressed to be a stable disper-
sion. Figure 1b shows an SEM image of 1d nanocrystals
collected by filtration after microwave irradiation. The
crystal size observed from this figure was similar to that
obtained by DLS measurement. In the conventional repre-
cipitation without microwave irradiation, remaining THF
seemed to assist aggregation of nanocrystals.
Nanocrystals of 1b, 1c, 1e, and 1f were also fabricated by
reprecipitation followed by microwave irradiation, and their
SEM images are shown in Figure 2a-d. These nanocrystals
were successfully obtained with a size range around 100-200
nm as a stable dispersion. On the other hand, fabrication of
1g nanocrystals was not succeeded in the same condition
because of nanocrystal aggregation resulting in precipita-
tion. However, injection of 1g solution with half the con-
centration of the standard condition (2.5 mmol/L) gave a
nanocrystal dispersion (Figure 2e).
Nanocrystals. To aqueous dispersions of diolefin nanocrystals,
UV light at 302 nm from a 6 W lamp (UVP UVM-57) was irradiated
with rigorous stirring for 1 h at room temperature. The UV-visible
spectra of the dispersions were monitored over the course of
photoirradiation.
3. Results and Discussion
Fabrication of Diolefin Nanocrystals by the Reprecipitaion
Method. Optimum Conditions and Procedures. In order to
determine the suitable conditions for diolefin monomers in
the reprecipitation method, several combinations of good
and poor solvents were attempted for 1d as a standard
compound. The solvents examined were THF and chloro-
form as good solvents, and water, methanol, ethanol, di-
methyl sulfoxide, N,N-dimethylformamide, and acetonitrile
as poor solvents. In each combination, any other conditions
were constant as in the typical procedure described in the
Experimental Section. As a result, the dispersion of 1d
nanocrystals was obtained only when THF solution was
injected into pure water. From the DLS measurement, an
average of crystal size in the resulting aqueous dispersion of
1d was estimated to be around 200 nm. However, when
nanocrystals of 1d were collected by filtration just after
reprecipitation, the nanocrystals were easily aggregated dur-
ing filtration as shown in a SEM image of Figure 1a. In fact,
In contrast to the above compounds, the nanocrystals of
1a and 2 were simply prepared by the reprecipitation method
without microwave irradiation. The shape of nanocrystals of
1a was plate-like and the size was about 300 nm to 1 μm on a
side (Figure 3). Nanocrystals of 2 had rod shapes, and the
length was from 150 nm to about 400 nm (Figure 2f).

Article
Concentration Effect of Injected Solution to Crystal Size.
Crystal Growth & Design, Vol. 10, No. 2, 2010 513
growth may start from the supersaturated and dissolved
state with small number of nuclei, resulting in large crystals.
Meanwhile, high concentration may cause rapid reprecipi-
tion producing a large number of nuclei at once, and the
following crystal growth would be limited to give relatively
smaller crystals.
It was reported that the crystal size and shape could be
controlled by changing some factors in the reprecipitaion
processes for nanocrystallization.17 In particular, the con-
centration of the compound solution injected, temperature
of the poor solvent, and addition of surfactant were the
important factors. In this study, the size change of nano-
crystals was investigated for 1a and 1d by changing the
concentration of the compound solution. Nanocrystals of
1d were prepared by various injection concentrations from 2
to 20 mmol/L, and they were observed by SEM. The crystals
prepared from the relatively low concentration solution
between 2 and 5 mmol/L had size around 200 nm, while
the size from the higher concentration such as 20 mmol/L
was 1-3 μm, as shown in Figure 1b,d.
Preparation of 1a nanocrystals was also carried out under
the solution concentration from 5 to 25 mmol/L. The SEM
images of the resulting nanocrystals are shown in Figure 3. In
contrast to 1d, the size of 1a crystals became larger when the
concentration of the injected solution was lower. When the
5 mmol/L solution was injected, the average crystal size was
varied in the range between 300 nm and 1 μm, although there
was a higher probability to obtain nanocrystals possessing
size of about 500 nm in this condition. At higher concentra-
tions of 10 and 25 mmol/L, the resulting crystal sizes became
around 200 and 150 nm, respectively. By injecting the solu-
tion with lower concentration than 4 mmol/L, nanocrystal
dispersion was not obtained but precipitation occurred,
indicating formation of large-sized crystals.
Photochemical Behavior. In Bulk Crystals. Photopoly-
merizability of bulk crystals (1a-1g and 2) was confirmed
by the IR spectral change (Table 1). IR absorption peaks
corresponding to the conjugated carbonyl groups and the
olefinic double bonds of 1a-1g were observed 1703-1714
cm-1 and 1628-1641 cm-1, respectively. Upon UV irra-
diation, a peak around 1710 cm-1 was shifted into the
higher-frequency region suggesting formation of the isolated
carbonyl groups. Another characteristic peak of the olefi-
nic double bonds completely disappeared, and this IR
spectral change was also observed for 2. Photoreaction of
1a-1c and 2 proceeded completely within 5 min, but photo-
reaction of 1d-1f took for 15 min. Cholesterol derivative 1g
needed UV irradiation for 2 h to achieve quantitative con-
version.
Photopolymerizability of bulk crystals in preparative scale
was also studied by IR spectra. Bulk crystals of 1a-1c and 2
were highly photoreactive within a rather short period (3 h)
of UV irradiation, whereas the other bulk crystals have very
low reactivity. Monomers 1d-1f in bulk crystals were not
converted within 30 h completely. Monomer 1g was less
reactive than 1a-1c and 2, while 1g was converted to the
corresponding polymer in prolonged photoirradiation for
30 h. One of the possible reasons for reverse order of the
photoreactivity in the preparative scale between 1d-1f and
1g compared with that in KBr pellets is lack of crystal
dispersion stability of 1d-1f in the preparative scale. In the
preparative conditions, crystals partially aggregated, result-
ing in insufficient UV irradiation to the whole.
In Nanocrystals. In UV-visible spectra of 1a, the absorp-
tion band at 381 nm originating from the π-conjugated
system almost disappeared after photoirradiation for 5 min
(Figure 4a). Other diolefins (1b-1g and 2) exhibited similar
changes to 1a in UV-visible spectra. UV-visible spectra of
1b, 1g, and 2 on behalf of other diolefins showed the
absorption bands at 280 nm, between 310 and 340 nm, and
between 300 and 420 nm, respectively (Figure 4b-d). IR
spectral changes of nanocrystals of 1a and 2 before and after
photoirradiation were confirmed to be the same as those of
bulk crystals. These results support quantitative conversion
of diolefins in nanocrystals to the corresponding photopro-
ducts. In contrast to the photoreactivity of bulk crystals on
In general, nanocrystal size becomes small when the
concentration of the injected solution is low,17 and crystal
size change of 1d seems to obey this tendency. However, the
case of 1a is completely opposite. We think that this may be
due to the relatively high affinity of 1a to water. When the
concentration of the injected solution is low, the amount of
good solvent relative to 1a becomes large and nanocrystal
Figure 3. SEM images of 1a nanocrystals: Injection of (a) 5 mmol/L
solution, (b) 10 mmol/L solution, and (c) 25 mmol/L solution.
Table 1. Photoreactivity of Diolefin Derivatives in Bulk Crystals
photoirradiationa in KBr pellet
photoirradiationa in preparative scale
reactivityc
before photoirradiation/cm-1
after photoirradiation/cm-1
compound
CdO
CdC
CdO
CdC
reactivityb
1a
1b
1c
1d
1e
1f
1g
2
1707
1710
1703
1711
1701
1711
1714d
-
1628
1637
1640
1639
1641
1639
1634d
1630
1732
1719
1734
1734
1733
1734
1733d
-
disappear
disappear
disappear
disappear
disappear
disappear
disappeard
disappear
þþþ
þþþ
þþþ
þþ
þþþ
þþþ
þþþ
þ
þþ
þ
þþ
þ
þ
þþ
þþþ
þþþ
a Irradiation from a 500 W ultra-high-pressure Hg lamp. b þþþ, reaction completed within 5 min; þþ, reaction completed within 15 min; þ, reaction
completed within 2 h. c þþþ, reaction completed within 2-3 h; þþ, reaction completed within 30 h; þ, reaction did not complete. d Measured for the
sample obtained in preparative scale.

514 Crystal Growth & Design, Vol. 10, No. 2, 2010
Miura et al.
Figure 4. Variation in UV-visible spectra of diolefin nanocrystal dispersion with UV irradiation time: (a) 1a, (b) 1b, (c) 1g, and (d) 2.
Table 2. Pairs of SEM Images for Morphology Comparison between
the Original Monomer Nanocrystals and the Resulting Polymers after
UV Irradiation
SEM images
compound
monomer
polymer
1a
1b
1d
1g
2
Figure 3a
Figure 2a
Figure 1b
Figure 2e
Figure 2f
Figure 5a
Figure 5b
Figure 5c
Figure 5d
Figure 5e
aggregated during photoirradiation, while the shape and size
of 1g nanocrystals was maintained.
Molecular Alignment in Crystals. In order to clarify the
photoreactivity from the structures, powder X-ray diffrac-
tion analysis of nanocrystals before and after photoirradia-
tion was carried out. As typical examples, X-ray diffraction
patterns of 1a, 1b, and 1d nanocrystals and their photo-
products are shown in Figures 6, 7, and 8, respectively, in
comparison with the corresponding bulk crystals.
As shown in Figure 6, the diffraction patterns of 1a
nanocrystals agree well with those of its photopolymerizable
bulk crystals. By photoirradiation, 1a nanocrystals expect-
edly afforded the photoproducts with the crystal structure
coinciding with photopolymer P1a from bulk crystal 1a.
Likewise, the nanocrystal structures of 2 and its photo-
product were also confirmed to coincide with those of the
corresponding bulk crystals of 2 and P2, respectively.
Furthermore, the crystal structures in nanocrystals were also
confirmed by an electron diffraction experiment. Although
Figure 5. SEM images of (a) 1a, (b) 1b, (c) 1d, (d) 1g, and (e) 2
nanocrystals after photoirradiation.
the preparative scale, it should be noted that all nanocrystals
(1a-1g and 2) are highly photoreactive.
Morphology. Morphology of resulting photoproducts in
nanocrystals was observed by SEM, and images are shown in
Figure 5. Table 2 summarizes pairs of the SEM images when
the morphology difference between the original monomer
nanocrystals and the resulting photoproducts is compared.
As reported previously,9 the size of photopolymer nanocrys-
tals of P1a and P2 are almost the same as that of the
corresponding monomer nanocrystals of 1a and 2. As shown
in Figure 5, 1b and 1d nanocrystals decayed in shape and

Article
Crystal Growth & Design, Vol. 10, No. 2, 2010 515
Figure 6. X-ray diffraction patterns of 1a: (a) bulk crystals before
photoirradiation, (b) bulk crystals after photoirradiation, (c) nano-
crystals before photoirradiation, and (d) nanocrystals after photo-
irradiation.
Figure 8. X-ray diffraction patterns of 1d: (a) bulk crystals before
photoirradiation, (b) bulk crystals after photoirradiation, (c) nano-
crystals before photoirradiation, and (d) nanocrystals after photo-
irradiation.
Figure 9. Electron diffraction patterns of (a) P1a and (b) P2
obtained from the corresponding monomer nanocrystals.
evidence that the reaction proceeded according to a typical
topochemical manner. On the other hand, X-ray diffraction
patterns of 1b nanocrystals were quite different from that of
1b bulk crystals (Figure 7c,d). The photoreaction of 1b
nanocrystals did not proceed topochemically, affording an
amorphous product (P1b0).
Figure 7. X-ray diffraction patterns of 1b: (a) bulk crystals before
photoirradiation, (b) bulk crystals after photoirradiation, (c) nano-
crystals before photoirradiation, and (d) nanocrystals after photo-
irradiation.
The diffraction pattern change of 1d nanocrystals by
photoirradiation was similar to that of 1b nanocrystals
as shown in Figure 8c,d, i.e., the crystalline monomer
changed into an amorphous polymer. For 1d, bulk crystals
also gave amorphous products (P1d0) by photoirradiation
(Figure 8a,b) although the monomer crystal structure in bulk
crystals differs from that in nanocrystals (cf. Figure 8a,c). It
was indicated that both bulk crystals and nanocrystals of 1d
did not form a crystal structure appropriate for topochem-
ical polymerization. Cholesterolyl derivative 1g showed
different diffraction patterns between bulk crystals and
nanocrystals, and nanocrystals were found to have lower
crystallinity than bulk crystals. The photoreaction of both
nanocrystals and bulk crystals of 1g gave amorphous pro-
ducts (P1g0).
Difference in crystal structures between bulk crystals and
nanocrystals and polymerization behaviors depending on
the compounds can be explained as follows. In the case of 1a
and 2, the crystal structures of nanocrystals coincided with
that of the corresponding bulk crystals before and after
photoreaction. In general, the planar compounds possessing
extended π-conjugation like 1a and 2 tend to form the plane-
parallel stack,18 and such a molecular stack is considered to
be easily formed irrespective of crystal size, i.e., bulk crystals
or nanocrystals. Monomers 1a and 2 have the R-type crystal
the electron diffraction patterns of the monomer (1a and 2)
nanocrystals could not be clearly recognized due to immedi-
ate damage, those of the polymer (P1a and P2) nanocrystals
were obtained. In Figure 9, electron diffraction patterns of
P1a and P2 were observed. When a diffraction ring from
the silver film with the spacing of 0.235 nm was used as a
reference, the diffraction spots in the inner area with the
shortest distance from the center corresponded to the long
spacings of 0.44 nm for P1a and 0.50 nm for P2, respectively.
These results agreed with the X-ray diffraction results of the
corresponding polymeric bulk crystals. Namely, 1a and 2
were topochemically polymerized into P1a and P2 by photo-
irradiation in both bulk crystals and nanocrystals. As men-
tioned above, the size of their nanocrystals was preserved
between monomers and the corresponding polymers. How-
ever, their monomer bulk crystals are broken into fragments
during the photoirradiation, and this point is quite different
between nanocrystals and bulk crystals. Nanocrystallization
can realize single-crystal-to-single-crystal transformation
even for the compounds without showing single-crystal-to-
single-crystal transformation in bulk crystals.
For bulk crystals of 1b, highly crystalline state was main-
tained during photoreaction to P1b crystal (Figure 7a,b), the

516 Crystal Growth & Design, Vol. 10, No. 2, 2010
Miura et al.
polymorphisms in β-type structures. Structure difference of
1a, 1b, and 1g in nanocrystals is also confirmed by the
UV-visible spectra of the dispersion as already shown in
Figure 4a-c. Although these three monomers have the
same π-conjugation system, the spectra are quite different.
The order of absorption maximum wavelength is 1a>1g> 1b.
In particular, the relatively sharp and blue-shifted absorp-
tion peak of 1b suggested formation of an H-type aggregate,
whose structure is the face-to-face parallel stack as shown in
Figure 10c. In bulk crystals, 1b was converted to crystalline
polymers, although its nanocrystals gave amorphous poly-
mers. The long spacing values obtained for bulk crystals and
nanocrystals of 1b were 1.81 and 3.19 nm, respectively
(Figure 7a,c). It is natural that the R-type crystal structure
has a smaller long-spacing value than the β-type crystal
structure because of the inclined molecular motif as shown
in Figure 10a. Thus, bulk crystals of 1b can be assigned as R-
type to give crystalline products, and nanocrystals of 1b can
be assigned as β-type crystals to give amorphous products,
respectively.
Conclusion
Nanocrystals of diolefin derivatives were successfully pre-
pared by the reprecipitation method and subsequent micro-
wave irradiation depending on the compounds. These
nanocrystals were found to be photoreactive. Particularly,
nanocrystals of 1a and 2 maintained the same crystal structure
as their polymerizable bulk crystals, affording polymer crys-
tals P1a and P2 and retaining the crystal size during photo-
irradiation. This is in contrast to the photopolymerization of
their bulk crystals, i.e., one single bulk crystal is fragmented
into small crystallites. This fact indicates that nanocrystalliza-
tion is advantageous to transform single crystals to single
crystals in the course of solid-state reactions. If single-crystal-
to-single-crystal transformation is achieved in nanosized sin-
gle crystals without fragmantation, molecular-weight control
of polymers is realized even in the case of diolefin derivatives.
Among the other diolefin nanocrystals, structures of 1b, 1d,
and 1g in both bulk crystals and nanocrystals were compared.
All these monomers gave crystals with different structures
between bulk crystals and nanocrystals. Among them, only 1b
bulk crystals have R-type structure to give crystalline polymer
by photoirradiation. Other bulk crystals and all nanocrystals
did not maintain their crystalline state during photoreaction
to give amorphous polymers. These bulk crystals and nano-
crystals of diolefins with large substituents were estimated to
form the β-type crystals.
Figure 10. Molecular alignment models of diolefin monomers.
Parts (a) and (b) are for inclined arrangement (R-type crystal
structure) of monomers and the corresponding polymers, respec-
tively. Parts (c) and (d) are for face-to-face parallel arrangement
(β-type crystal structure) of monomers and the corresponding
oligomers, respectively. Single-crystal-to-single-crystal transition
is proceeded in the former case, while single-crystal-to-amorphous
transition is proceeded in the latter case.
structure with the center of symmetry between adjacent
monomers (Figure 10a), and it is apt to show topochemical
polymerization because the centers of gravity of the mono-
mers do not move enough in the course of solid-state
polymerization to give crystalline polymers (Figure 10b).
On the other hand, the structure of nanocrystals of 1b, 1d,
and 1g modified with relatively large substituents was dif-
ferent from that of bulk crystals even before photoirradia-
tion. In these cases, their large substituents should show a
predominant effect for their molecular packing in crystals
rather than π-conjugated phenylenediacrylate moiety. Com-
pounds having long alkyl chains are known to often show
polymorphism, and 1b, 1d, and 1g are no exceptions. In
addition, nanocrystals of 1b, 1d, and 1g were converted to
amorphous products by photoirradiation. Bulk crystals of
1d and 1g also became amorphous after photoirradiation. It
has been reported that amorphous products were obtained
by photoreaction from diolefins with the β-type crystal
structure, which has a mirror-plane symmetry between a
pair of molecules as shown in Figure 10c. When polymeriza-
tion is proceeded in this structure as reported for the photo-
reaction of dimethyl m-phenylenediacrylates in bulk
crystals,19 steric repulsion between substituents at the poly-
merization ends of adjacent oligomers or polymers should
suppress the polymerization process (Figure 10d). Regarding
1d and 1g, a β-type crystal might be more stable since 1d and
1g gave amorphous P1d0 and P1g0 even in bulk crystals by
photoirradiation. For 1d, the long spacings in bulk crystals
and in nanocrystals are 3.74 and 4.31 nm, respectively
(Figure 8a,c). These two structures are both classified into
the structure like Figure 10c, and they are considered to be
References
(1) Hasegawa, M.; Suzuki, Y. J. Polym. Sci., Part B 1967, B5,
813.
(2) Nakanishi, H.; Hasegawa, M.; Sasada, Y. J. Polym. Sci., Part A2
1972, 10, 1537.
(3) (a) Hasegawa, M.; Hashimoto, Y. Mol. Cryst. Liq. Cryst. 1992,
219, 1. (b) Hasegawa, M. Adv. Phys. Org. Chem. 1996, 30, 117.
(c) Hasegawa, M.; Chung, C.-M.; Kinbara, K. J. Photosci. 1997, 4,
147.
(4) (a) Wegner, G. Z. Naturforsch. 1969, 24b, 824. (b) Enckelmann, V.
In Polydiacetylenes, Cantow, H.-J., Ed.; Advances in Polymer
Science 63; Springer-Verlag: Berlin, 1984; pp 91-136. (c) Sarkar, A.;
Okada, S.; Matsuzawa, H.; Nakanishi, H. J. Mater. Chem. 2000, 10,
819.
(5) (a) Matsumoto, A.; Matsumura, T. J. Chem. Soc., Chem. Commun.
1994, 1389. (b) Matsumoto, A.; Odani, T.; Chikada, M.; Sada, K.;
Miyata, M. J. Am. Chem. Soc. 1999, 121, 11122.

Article
Crystal Growth & Design, Vol. 10, No. 2, 2010 517
(6) Iida, R.; Kamatani, H.; Kasai, H.; Okada, S.; Oikawa, H.;
Matsuda, H.; Kakuta, A.; Nakanishi, H. Mol. Cryst. Liq. Cryst.
1995, 267, 95.
(7) Matsumoto, A.; Yokoi, K.; Aoki, S. Polym. J. 1998, 30, 361.
(8) Nakanishi, H.; Hasegawa, M.; Kirihara, H.; Yurugi, M. Nippon
Kagaku Zasshi 1977, 7, 1046.
(9) Takahashi, S.; Miura, H.; Kasai, H.; Okada, S.; Oikawa, H.;
Nakanishi, H. J. Am. Chem. Soc. 2002, 124, 10944.
(10) Ruggli, P.; Theilheimer, W. Helv. Chem. Acta 1941, 24, 899.
(11) Suzuki, F.; Suzuki, Y.; Nakanishi, H.; Hasegawa, M. J. Polym.
Sci., Part A1 1969, 7, 2319.
(12) Nakanishi, F. J. Chem. Soc., Chem. Commun. 1984, 1543.
(13) (a) Nakanishi, F.; Morishita, N.; Shoji, S. Polym. Commun. 1988,
29, 52. (b) Nakanishi, F.; Shoji, S. Bull. Res. Inst. Polym. Text. 1991,
165, 13.
(15) (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. 1992, 31, L1132. (b) Kasai, H.; Nalwa, H. S.; Okada, S.;
Oikawa, H.; Nakanishi, H. Fabrication and Spectroscopic Characteriza-
tion of Organic Nanocrystals. In Handbook of Nanostructured Materials
and Nanotechnology, Nalwa, H. S., Ed.; Vol. 5, Organics, Polymers, and
Biological Materials; Academic Press: San Diego, 1999, pp 433-473.
(16) Baba, K.; Kasai, H.; Okada, S.; Oikawa, H.; Nakanishi, H. Jpn. J.
Appl. Phys. 2000, 39, L1256.
(17) (a) Kasai, H.; Oikawa, H.; Okada, S.; Nakanishi, H. Bull. Chem.
Soc. Jpn. 1998, 71, 2597. (b) Katagi, H.; Kasai, H.; Okada, S.; Oikawa,
H.; Komatsu, K.; Matsuda, H.; Liu, Z.; Nakanishi, H. Jpn. J. Appl.
Phys. 1996, 35, L1364.
(18) Hasegawa, M. Chem. Rev. 1983, 83, 507.
(19) Nakanishi, F.; Nakanishi, H.; Hasegawa, M.; Yamada, Y.
(14) Franke, R. Chem. Ber. 1905, 38, 3727.
J. Polym. Sci., Polym. Chem. Ed. 1975, 13, 2151.