Photocontrol of micelle triggered by Malachite Green carrying a long alkyl chain

Article abstract of DOI:10.1246/bcsj.78.1862

A Malachite Green derivative carrying a long alkyl chain has been designed to realize the photoinduced uptake of oily substances based on its photogenerated amphiphilicity. NMR spectroscopy was used to evaluate the solubility of benzene in cetyltrimethyla

Full text of DOI:10.1246/bcsj.78.1862

1862 Bull. Chem. Soc. Jpn., 78, 1862–1867 (2005)
ꢀ 2005 The Chemical Society of Japan
Photocontrol of Micelle Triggered by Malachite Green
Carrying a Long Alkyl Chain
ꢀ;1
Ryoko M. Uda and Keiichi Kimura
Department of Chemical Engineering, Nara National College of Technology,
Yata 22, Yamato-koriyama, Nara 639-1080
1Department of Applied Chemistry, Faculty of Systems Engineering, Wakayama University,
Sakae-dani 930, Wakayama 640-8510
Received February 14, 2005; E-mail: kkimura@sys.wakayama-u.ac.jp
A Malachite Green derivative carrying a long alkyl chain has been designed to realize the photoinduced uptake of
oily substances based on its photogenerated amphiphilicity. NMR spectroscopy was used to evaluate the solubility of
benzene in cetyltrimethylammoium chloride solution with Malachite Green carrying a long alkyl chain. We found that
UV irradiation drastically increased the solubility of benzene in the system of Malachite Green carrying a long alkyl
chain. The results for the photoinduced solubilization are in good agreement with the photoionization ratio of Malachite
Green carrying a long alkyl chain, which can play an important role in the control of molecular assemblies.
The widespread use of surfactant mixtures for the industrial
purposes has stimulated the interest of researchers in the con-
H3C CH3
N
trol of formation and rupture of surfactant assemblies such as
micelles. In aqueous solution, micelles solubilize lipophilic
O
C
CN
substances in their interior, which consists of a hydrophobic
group of the surfactant. Several studies aiming at the control
of uptake and release of lipophilic substances were carried
out by external stimuli using pH,1 temperature,2 and additives.3
In particular, light is one of the most desirable methods of
stimulus for clean and rapid control of micelle formation. Pho-
tochromic compounds such as azobenzene,4–6 spirobenzopy-
ran,7 and stilbene8 were introduced to amphiphilic molecules
for the photochemical control of micelle formation. Though
the photoinduced trans-cis isomerization of azobenzene and
stilbene derivatives induces a structural change,4–6,8 both of
the isomers are still amphiphilic. The photocontrol in the sys-
tem of spirobenzopyran derivatives,7 which generates a zwitter
ion, was only achieved by shifting the amphiphilicity between
the two isomers. Nevertheless, there are few reports concern-
ing the photogeneration of amphiphilicity from a simply lipo-
philic substance. We have designed Malachite Green leuconi-
trile carrying a long alkyl chain 1 (Scheme 1),9 which controls
micelle formation photochemically. Malachite Green leuconi-
trile, a triphenylmethane dye, undergoes photoionization by
dissociating the cyanide ion with a high quantum efficien-
cy,10,11 thus affording a positive charge generation on the
molecule by UV irradiation. Therefore, Malachite Green 1,
when ionized photochemically, exhibits hydrophilicity by its
triphenylmethyl cation and hydrophobicity by its long alkyl
chain (Scheme 1). On the other hand, under dark conditions,
1 behaves only as a lipophilic compound. Once it is irradiated
by UV light, it turns out to be a cationic surfactant. Thus, a
drastic effect on micelle formation is expected. We have suc-
ceeded in the photocontrol of critical micelle concentration
(cmc) of cetyltrimethylammonium chloride (CTAC) by a
1
N
H3C CH3
UV
Heat
H3C CH3
N
+ CN-
O
C+
N
H3C CH3
Hydrophobic group
Hydrophilic group
Scheme 1. Photogenerated amphiphilicity on 1.
small amount of 1, i.e. 1:0 ꢁ 10ꢂ5 mol dmꢂ3 of 1 decreased
ꢃ
the cmc from 0.6 to 0.1 mmol dmꢂ3 by UV irradiation.9
ꢃ
In order to apply the photocontrol of micelle formation in
various fields including those of cosmetics, perfumes, and
foods, it is desirable to use conventional systems with com-
mercially available surfactants. Therefore, this requires a pho-
toresponsive compound which controls molecular assemblies
formed by conventional surfactants. In addition to the industri-
al application, so-called ‘‘photoresponsive command com-
pound’’ may afford more sophisticated systems because only
a small amount of it is able to control the molecular assem-
Published on the web October 4, 2005; DOI 10.1246/bcsj.78.1862

R. M. Uda et al.
Bull. Chem. Soc. Jpn., 78, No. 10 (2005) 1863
pared solutions. By a similar procedure, other series of sample so-
lutions including known amounts of benzene were prepared; to
each of 10-cm3 sample vials equipped with silicone-rubber cap
was added 1 cm3 of sample solution. Benzene was added in a dif-
ferent amount to each of the vials, which was then sealed. The so-
lution was withdrawn by a syringe from the vial just before its
measurement. When excess benzene that did not dissolve in the
aqueous solution was detected, the sample was withdrawn so as
not to include the benzene.
blies. The purpose of this work is to control solubilization of
oily substances in CTAC micelle by photoresponsive com-
mand compound 1.
Experimental
Synthesis.
Bis[4-(N,N-dimethylamino)phenyl][4-(hexade-
cyloxy)phenyl]methanenitrile or Malachite Green Carrying a
Long Alkyl Chain 1: Dimethyl sulfate (33.3 mmol) and 4-hexa-
decyloxybenzoic acid (7.3 mmol) were added to a mixture of dry
acetone (300 cm3) and K2CO3 (33.3 mmol). After the reaction
mixture was refluxed for 8 h, the acetone was evaporated off under
vacuum. The residue was extracted with water and benzene and
the solvent evaporation of the organic phase afforded methyl
4-hexadecyloxybenzoate. 4-Bromo-N,N-dimethylaniline (18.0
mmol) was dissolved in anhydrous tetrahydrofuran (THF) (31
cm3) and the solution was kept at ꢂ78 ꢄC in a methanol bath with
dry ice under an argon atmosphere. A hexane solution of butyl-
lithium (20.3 mmol) was injected gradually into the THF solution
while stirring. To the mixture was added dropwise a THF (38.5
cm3) solution of methyl 4-hexadecyloxybenzoate (7.7 mmol).
The reaction mixture was allowed to warm slowly to room tem-
perature and then stirred for an additional hour. After the reaction,
the THF was evaporated off under vacuum and water (100 cm3)
was added to the residue. The aqueous phase was then neutralized
Dynamic Light Scattering. Dynamic light scattering mea-
surements were made using an Ohtsuka DLS-700 instrument
equipped with a helium-neon laser (632.8 nm, scattering angle
of 45ꢄ) at 25 C.
ꢄ
1H NMR.
The experiment temperature was 25 ꢄC. NMR
measurements were carried out on a JEOL JNM-270 instrument
operating at 270.05 MHz.
Photoionization Ratio. The ionization ratio was calculated,
which is defined by AMGL/AMGO, where AMGL and AMGO are
the absorbance at 610 nm of 1:0 ꢁ 10ꢂ5 mol dmꢂ3 1 after UV
ꢃ
irradiation and 1:0 ꢁ 10ꢂ5 mol dmꢂ3 Malachite Green oxalate
ꢃ
Results and Discussion
in CTAC solution, respectively.
Photoisomerization of Malachite Green in CTAC
Solution. Figure 1 shows a typical absorption-spectral change
of the sample solution before and after UV irradiation. An ab-
sorption peak around 270 nm, which was decreased by UV ir-
radiation, can be assigned to the electrically neutral leuconi-
trile form of 1. Its ionized form was confirmed by the appear-
ance of a peak at 610 nm after UV irradiation, indicating the
photoinduced ionization of 1. The sample solutions were 0.1
by 0.1 mol dmꢂ3 hydrochloric acid. Extraction with benzene, fol-
ꢃ
lowed by vacuum evaporation of the solvent, afforded a dark-
green oily product of bis[4-(N,N-dimethylamino)phenyl][4-(hexa-
decyloxy)phenyl]methanol, which was used for the subsequent
cyanization without further purification. The crude product (ap-
proximately 7.75 mmol) was dissolved in dimethyl sulfoxide
(20 cm3) and heated at 60 ꢄC in a hood. Hydrochloric acid (94
mmol) and then KCN (347 mmol) were added to the solution
and the mixture was stirred for 10 min. For complete dissolution
of the KCN, an appropriate amount (up to 100 cm3) of water was
added. The reaction mixture turned light yellow and then a crude
product of Malachite Green 1 precipitated. Recrystallization of the
filtered precipitate from hexane yielded a white solid of 1 (27%):
mp 84 ꢄC, 1H NMR (270 MHz, CDCl3) ꢀ 0.87 (t, J ¼ 6:7 Hz, 3H,
CCH3), 1.24–1.42 (m, 26H, (CH2)13), 1.76 (m, 2H, CCH2C), 2.94
(s, 12H, NCH3), 3.93 (t, J ¼ 6:6 Hz, 2H, OCH2), 6.63 (d, J ¼ 9:0
Hz, 4H, m-H of NPh), 6.80 (d, J ¼ 8:7 Hz, 2H, m-H of OPh), 7.02
(d, J ¼ 8:7 Hz, 4H, o-H of NPh), 7.10 (d, J ¼ 8:7 Hz, 2H, o-H of
OPh). Anal. Calcd for C40H57N3O: C, 80.62; H, 9.64; N, 7.05%.
Found: C, 80.28; H, 9.67; N, 7.00%.
mol dmꢂ3 acetate buffer solutions (pH 4.8) containing 1:0 ꢁ
ꢃ
10ꢂ5 mol dmꢂ3 of 1 and 4.0 mmol dmꢂ3 of CTAC. Even
ꢃ
ꢃ
without photoirradiation, the ionization of 1 was strongly pro-
moted in solutions more acidic than pH 4.0. When the pH of
the sample solution was above 5.0, the photoionized 1 was im-
mediately hydroxylated and the positive charge on the Mala-
chite Green moiety disappeared. Therefore, an appropriate buf-
fer solution was necessary for all samples in this work. The
photoionized 1 was stable in the buffer solution and the ab-
0.5
0.4
0.3
0.2
0.1
0
Other Materials. Cetyltrimethylammonium chloride (CTAC)
was recrystallized from THF. Deuterium oxide had a purity of
99.9%. Water was deionized. Other materials were analytical
grade and were used without further purification.
Preparation of Sample Solutions. Sample solutions were
prepared using 0.1 mol dmꢂ3 acetate buffer (pH 4.8), unless oth-
ꢃ
erwise noted. Photoirradiation was continued for 15 min. UV light
source (<330 nm) was a xenon lamp (500 W) equipped with a
photoguide tube and a Toshiba UV-D33S filter. For dynamic light
scattering measurements, sample solutions were filtered first by a
0.45-mm Millipore filter and then by a 0.1-mm Millipore filter.
Sample solutions for NMR measurements were prepared in
D2O, instead of deionized water, containing 1,4-dioxane (1
vol %) as the internal reference. To each of 1-cm3 sample solution,
benzene was added in excess (approximately 0.1 cm3) and the ex-
cess of benzene was removed after the solubilization. The excess
benzene never caused reversed micelle or emulsion in the pre-
200
400
600
800
Wavelength / nm
Fig. 1. Absorption-spectral changes of 0.1 mol dmꢂ3 ace-
ꢃ
tate buffer solution containing 4.0 mmol dmꢂ3 of CTAC
ꢃ
and 1:0 ꢁ 10ꢂ5 mol dmꢂ3 of 1 under dark conditions
ꢃ
and after UV irradiation for 15 min. The arrows denote
changes by photoirradiation.

1864 Bull. Chem. Soc. Jpn., 78, No. 10 (2005)
Photocontrol of Micelle Formation
995
990
985
980
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965
(E)
(D)
0
10
20
30
40
(B)
CTAC concentration / mmol·dm−3
(F)
(C)
(A)
Fig. 3. Chemical shift of benzene protons as a function of
CTAC concentration in D2O solution of CTAC saturated
with benzene.
ppm
0
molecule14 in the micelle interior where benzene molecules
are stacked. The observed chemical shifts were referenced
with respect to the protons of 1,4-dioxane, which was used
as the internal standard,16 and were plotted as a function of
CTAC concentration in Fig. 3. The ꢀobs was almost unchanged
when the concentration of CTAC was less than its cmc (0.6
8
6
4
2
δ
Fig. 2. 1H NMR spectrum of D2O solution of CTAC
(20 mmol dmꢂ3) saturated with benzene. –(CH2)14– (A),
acetate (B), NCH3 (C), 1,4-dioxane (D), HDO (E), and
benzene (F).
ꢃ
mmol dmꢂ3). This is because, in the system without micelle
ꢃ
formation, the ꢀobs depends simply on the solubility of benzene
in the aqueous phase. Above the cmc, the ꢀobs was decreased
with increasing in CTAC concentration (Fig. 3), i.e. the ben-
zene peak was shifted to a higher magnetic field. Since the
higher concentration of CTAC results in the higher ratio of
Cmic=Ctot, the results in Fig. 3 agree with Eq. 1.
sorbance at 610 nm, corresponding to ionized 1, was main-
tained at room temperature for 1 week after the irradiation.
Dynamic light scattering measurements, carried out in 0.1
mol dmꢂ3 acetate buffer solutions containing 40 mmol dmꢂ3
ꢃ
ꢃ
CTAC and 1:0 ꢁ 10ꢂ5 mol dmꢂ3 1, afforded the diameters of
ꢃ
8.1 nm under dark conditions and 8.5 nm after UV irradiation
with an error of about 4%. Though the addition of an electro-
lyte to the surfactant solutions causes an increase in the size of
micellar aggregates,12,13 the obtained value for the micelle di-
ameter is appropriate for spherical micelles of CTAC. There-
fore, the effect of the buffer solution on the micelle size and
shape is negligible in this work.
The CTAC solution containing 1 affords almost the same
values for ꢀobs without 1 under dark conditions. The full sym-
bols in Fig. 4 (a, b, and c) were obtained under dark conditions
in the systems of different concentrations of 1 and the ꢀobs de-
pends on the concentration of CTAC, not on the concentration
of 1. The result indicates that the amount of 1 is too small to
affect the ratio of Cmic=Ctot. On the other hand, compound 1
plays an important role under UV-irradiated conditions. The
photoirradiation caused a significant peak shift to the higher
magnetic field (empty symbols in Fig. 4). Though the photoin-
duced shift is small in the solution containing 1:0 ꢁ 10ꢂ6
Photoinduced Uptake of Benzene in Micelle Solution. A
1
typical H NMR spectrum of a CTAC D2O solution saturated
with benzene is shown in Fig. 2. The leftmost peak can be as-
signed to benzene protons. Some of the benzene molecules are
in surfactant micelles and others in the bulk aqueous phase.
And then the chemical shift of the benzene proton is generally
different in these two environments. At the concentration of
CTAC higher than its cmc, we assume that the rate of benzene
exchange between the aqueous and micellar phase is faster
than NMR time scale,14,15 so the observed chemical shift
(ꢀobs) is the weighted average of the chemical shifts in the
aqueous phase (ꢀaq) and in the micellar phase (ꢀmic).
mol dmꢂ3 of 1 (Fig. 4a), a distinct shift is observed in the so-
ꢃ
lutions containing 5:0 ꢁ 10ꢂ6 and 1:0 ꢁ 10ꢂ5 mol dmꢂ3 of 1
ꢃ
(Figs. 4b and c). Moreover, the higher concentration of 1 af-
fords the more remarkable shift by UV irradiation. This result
indicates that UV irradiation promotes the solubilization of
benzene in micellar phase.
Since it is important to estimate the photoinduced solubili-
zation of benzene quantitatively, we discuss the relationship
between observed chemical shift and the solubility of benzene
in the sample solution. If we also assume that the benzene con-
centration in aqueous phase (Caq) is constant when Ctot is
much higher than the solubility of benzene in aqueous phase,
Eq. 3 is obtained from Eqs. 1 and 2:
ꢀ
ꢁ
ꢀ
ꢁ
Cmic
Ctot
Caq
Ctot
ꢀobs
¼
ꢀmic
þ
ꢀaq;
ð1Þ
ð2Þ
Ctot ¼ Cmic þ Caq:
Here, Cmic, Caq, and Ctot are the concentrations of benzene
in micellar phase, aqueous phase, and total concentration in
the solution.
The signal in micellar phase (ꢀmic) is at the higher magnetic
field than that in aqueous phase (ꢀaq). Nakagawa et al. ex-
plained that it is caused by the large ring-current of benzene
ꢀ
Here, Caq,sat is the saturated concentration of benzene (ben-
ꢁ
ꢀ
ꢁ
Ctot ꢂ Caq,sat
Ctot
Caq,sat
Ctot
ꢀobs
¼
ꢀmic
þ
ꢀaq:
ð3Þ
zene solubility) in aqueous phase. And Eq. 3 is then rewritten

R. M. Uda et al.
Bull. Chem. Soc. Jpn., 78, No. 10 (2005) 1865
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990
985
980
975
970
965
995
990
985
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a
0
10
20
30
40
CTAC concentration / mmol·dm-3
0.1
0.2
0.3
0.4
0.5
0.6
Ctot-1 / dm3·g-1
995
990
985
980
975
970
965
b
Fig. 5. Chemical shift of benzene protons as a function of
1=Ctot. Concentration of CTAC: 4 mmol dmꢂ3
( ); 8
mmol dmꢂ3 ( ); 14 mmol dmꢂ3 ( ); 20 mmol dmꢂ3
ꢃ
ꢃ
ꢃ
ꢃ
(
points.
); 40 mmol dmꢂ3
(
). The arrows indicate intersection
ꢃ
995
990
985
980
975
970
965
δ
sat = −43.25 Csat + 1178
0
10
20
30
40
CTAC concentration / mmol·dm-3
995
990
985
980
975
970
965
c
3
4
5
6
Csat / g·dm-3
Fig. 6. Dependence of ꢀsat on Csat. The data points corre-
spond to the intersections in Fig. 5.
0
10
20
30
40
CTAC concentration / mmol·dm-3
and thereafter it increases with 1=Ctot. The data points in Fig. 5
were subjected to least-squares fitting to obtain two straight
lines with an intersection, which in turn affords the values of
Csat and ꢀsat. The solubility of benzene, Csat, was increased
with the concentration of CTAC (Fig. 5). Since the ꢀobs values
did not show any clear dependence on 1=Ctot in the solution
Fig. 4. Chemical shift of benzene protons under dark con-
ditions (full symbols) and after UV irradiation (empty
symbols). Concentration of 1: 1:0 ꢁ 10ꢂ6 mol dmꢂ3 (a);
ꢃ
5:0 ꢁ 10ꢂ6 mol dmꢂ3 (b); 1:0 ꢁ 10ꢂ5 mol dmꢂ3 (c).
ꢃ
ꢃ
containing less than 4 mmol dmꢂ3 of CTAC, we did not find
as Eq. 4:
ꢃ
ꢀ
ꢁ
any intersection point and could not therefore obtain any value
of Csat and ꢀsat at any magnetic field lower than 987 Hz.
By using the data at the intersection points in Fig. 5, we
could plot the ꢀsat values against Csat in Fig. 6. A linear relation
is obtained between Csat and ꢀsat, in the range from 966 to 987
Hz (Fig. 6). Accordingly, we can approximate the dependence
Caq,sat
Ctot
ꢀobs
¼
ðꢀaq ꢂ ꢀmicÞ þ ꢀmic
:
ð4Þ
Thus, a plot of ꢀobs vs 1=Ctot should give a straight line.
Finally, we obtain the relationship between the chemical shift
of the solution at saturation (ꢀsat) and the solubility of benzene
in the solution (Csat), which is expressed by Eq. 5:
of ꢀsat on Csat by a simple expression: ꢀsat ¼ ꢂ43:25Csat
þ
ꢀ
ꢁ
1178. Owing to this linear approximation, the values of chemi-
cal shifts in Fig. 4 afford their corresponding Csat, because the
chemical shifts for Fig. 4 are those of the solutions at satura-
tion (ꢀsat) after removal of the excess undissolved benzene
from the sample solutions. Figure 7 shows the UV-induced
change in the solubility of benzene for the systems containing
concentrations of CTAC and 1. Under dark conditions, the sol-
Cnq,sat
Csat
ꢀsat
¼
ðꢀaq ꢂ ꢀmicÞ þ ꢀmic
:
ð5Þ
Typical plots of ꢀobs vs 1=Ctot are shown in Fig. 5. When the
concentration of benzene applied to the sample is above Csat
(Ctot > Csat), the excess benzene is separated from micelle so-
lution. Accordingly, the chemical shift is constant up to 1=Csat
,

1866 Bull. Chem. Soc. Jpn., 78, No. 10 (2005)
Photocontrol of Micelle Formation
1
0.8
0.6
0.4
0.2
0
5
4.8
4.6
4.4
4.2
4
a
0
10
20
30
40
0
10
20
30
40
CTAC concentration / mmol·dm-3
CTAC concentration / mmol·dm-3
Fig. 8. Dependence of photoionization ratio of 1 on CTAC
concentration.
5
4.8
4.6
4.4
4.2
4
cant increase (0.26 g dmꢂ3) in the solubility of benzene.
ꢃ
As a consequence, it suggests that 1 behaves as a command
compound for the photoinduced uptake of oily substance in
micelles.
Photoionization Ratio of Malachite Green. As shown in
Figs. 4 and 7, the photoinduced uptake was enhanced in the so-
lution with more than 4 mmol dmꢂ3 of CTAC. We consider
b
ꢃ
that the solubilizing ability under UV-irradiated condition is
concerned with the amount of ionized 1. Since the molar ab-
sorptivity of Malachite Green cation (triphenylmethyl cation)
in visible light region is almost the same as that of ionized
1, the photoionization ratio of 1 can be calculated by the ab-
sorbance of Malachite Green oxalate (See: experimental sec-
tion). The photoionization ratio of 1 in the solution is plotted
against CTAC concentration in Fig. 8. The ratio does not show
0
10
20
30
40
CTAC concentration / mmol·dm-3
5
4.8
4.6
4.4
4.2
4
any significant increase up to 4 mmol dmꢂ3, above which it
ꢃ
increases abruptly. These results coincide with Fig. 4c, indicat-
ing that the photoionization of 1 contributes to increasing the
photoinduced uptake of benzene into micelle solution. The
main reason for the increasing photoionization ratio with the
CTAC concentration is that the electrically neutral 1 is difficult
to dissolve in water under dark conditions and that an appro-
priate concentration of micelle is required to dissolve it. UV
irradiation promotes the ionization of 1 in the CTAC micelle,
resulting in the abrupt increasing in the photoionization ratio.
Besides, a gradual increase of ionization ratio was observed
c
0
10
20
30
40
CTAC concentration / mmol·dm-3
Fig. 7. Solubility of benzene in CTAC solution under dark
conditions (full symbols) and after UV irradiation (empty
above 20 mmol dmꢂ3 of CTAC and this is in good agreement
symbols). Concentration of 1: 1:0 ꢁ 10ꢂ6 mol dmꢂ3 (a);
ꢃ
ꢃ
5:0 ꢁ 10ꢂ6 mol dmꢂ3 (b); 1:0 ꢁ 10ꢂ5 mol dmꢂ3 (c).
with the data for Fig. 7c, i.e. the benzene solubility is not high-
ly enhanced by UV irradiation above 20 mmol dmꢂ3. There-
ꢃ
ꢃ
ꢃ
ubilization curve is almost the same in each solution contain-
ing a different concentration of 1. UV irradiation increases the
solubility of benzene in each of the systems. The effect of
photoirradiation on solubilization is not significant in Fig. 7a
fore, the photoionized 1 participates in the CTAC micelle
formation and causes the efficient photochemical uptake of
benzene.
We conclude that the drastic photoinduced uptake of ben-
zene is realized by a small amount of lipophilic Malachite
Green 1, which exhibits a distinct amphiphilicity photogener-
ated from the simply lipophilic substance. Since compound 1
works as a command compound to control the molecular as-
semblies, we expect to use this remarkable feature for the sys-
tems formed by amphiphilic compounds such as reversed
micelle, liposome, LB membrane, and microcapsule. Further-
more, we also expect to apply this photoresponsive surfactant
for controlling cation extraction and designing drug delivery
systems.
(1:0 ꢁ 10ꢂ6 mol dmꢂ3 of 1), but the most drastic photo-
ꢃ
ꢃ
induced enhancement of solubility is found in Fig. 7c
(1:0 ꢁ 10ꢂ5 mol dmꢂ3 of 1). The results lead to the conclu-
sion that photoionized 1 contributes to increasing the solubility
of benzene in micelle solutions. The most remarkable change
by photoirradiation in Fig. 7 was attained with 8 mmol dmꢂ3
ꢃ
of CTAC containing 1:0 ꢁ 10ꢂ5 mol dmꢂ3 of 1, the benzene
ꢃ
solubility changing from 4.55 g dmꢂ3 under dark conditions
ꢃ
to 4.81 g dmꢂ3 by photoirradiation. It should be noted that a
ꢃ
small amount of 1 (1:0 ꢁ 10ꢂ5 mol dmꢂ3) induces a signifi-
ꢃ

R. M. Uda et al.
Bull. Chem. Soc. Jpn., 78, No. 10 (2005) 1867
7
S. Tazuke, S. Kurihara, H. Yamaguchi, and T. Ikeda,
This work was supported by Grant-in-Aids for Scientific
Research (No. 15750164 and No. 15350043) from the Japan
Society of the Promotion of Science. One of the authors
(R. M. U.) also acknowledges Hayashi Memorial Foundation
for Female Natural Scientists for financial support.
J. Phys. Chem., 91, 249 (1987).
J. C. Russell, S. B. Costa, R. P. Seiders, and D. G. Whitten,
J. Am. Chem. Soc., 102, 5678 (1980).
8
9
(2004).
R. M. Uda, M. Oue, and K. Kimura, Chem. Lett., 33, 586
10 K. G. Spears, T. H. Gray, and D. Huang, J. Phys. Chem.,
90, 779 (1996).
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