Photochromism of diarylethenes on gold and silver nanoparticles

Article abstract of DOI:10.1246/bcsj.79.1413

Gold and silver nanoparticles capped with photochromic diarylethene ligands were prepared and their photochromic performance was investigated. Although the quenching of cyclization reactions by the metal particles took place to some extent, the diarylethe

Full text of DOI:10.1246/bcsj.79.1413

ꢀ 2006 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 79, No. 9, 1413–1419 (2006) 1413
Photochromism of Diarylethenes on Gold and Silver Nanoparticles
ꢀ1;2
ꢀ1
and Masahiro Irie
Hidehiro Yamaguchi,1 Masumi Ikeda,1 Kenji Matsuda,
1Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University,
744 Motooka, Nishi-ku, Fukuoka 819-0395
2PRESTO, JST, 4-1-8 Honcho, Kawaguchi 332-0012
Received February 2, 2006; E-mail: kmatsuda@cstf.kyushu-u.ac.jp
Gold and silver nanoparticles capped with photochromic diarylethene ligands were prepared and their photochro-
mic performance was investigated. Although the quenching of cyclization reactions by the metal particles took place to
some extent, the diarylethene on the nanoparticles underwent reversible photochromic reactions by irradiation with UV
and visible light.
Photochromic compounds, which undergo reversible photo-
isomerizations, inherently have bistability such that the com-
Results and Discussion
pounds can be utilized as switching units in molecular-scale
optoelectronic devices.1 Diarylethenes have been extensively
studied because this series of compounds have highly sensi-
tive, thermally stable, and fatigue resistant photochromic char-
acteristics.2 In order to fabricate practical devices, molecule–
electrode contacts are indispensable, and several methods have
been designed to attach organic molecules to metal surfaces.
Among them, self-assembled monolayers (SAM) on metal sur-
faces have advantages in terms of facile preparation and stabil-
ity of the junctions.3 However, metals are known to quench
readily the electronic excited states of the molecule placed
on their surfaces.4 This problem must be solved in order to per-
form photochemical reactions on metal surfaces.
Metal nanoparticles are of interest in multidisciplinary fields
because the physical properties of the nanoparticles are differ-
ent from those of the bulk state.5 The introduction of facile
preparation methods by Brust et al.6 accelerated the study on
the nanoparticles of noble metals. Photophysical properties
of the metal nanoparticles are also different from the bulk
state. For example, plasmon absorption is clearly observed de-
pending on the size of the particles. Gold nanoparticles have a
surface plasmon resonance absorption band at around 520 nm,7
while silver nanoparticles have a surface plasmon resonance
absorption at around 420 nm, which is shorter than that of gold
nanoparticles.8 Some of the gold and silver nanoparticles are
reported to exhibit fluorescence.9 The interplay between the
plasmon absorption and the photochemical property of ligand
is an attractive subject, and chromophore-functionalized metal
nanoparticles have been extensively studied.10
Design and Synthesis of Ligand 1a. In order to investigate
the photochromic reaction of diarylethenes on the gold and
silver nanoparticles, there are two points to consider for the
molecular design: 1) distance between the chromophore and
the metal nanoparticle and 2) size of the metal nanoparticles.
Figure 1 shows the diarylethene derivative 1a used in this
experiment. Diarylethene 1a has a thiol unit, which forms self-
assembled monolayer on the metal nanoparticle core. Methyl
groups are introduced at the 3-positions on thiophene ring to
increase fatigue-resistance. The distance between the diaryl-
ethene moiety and the metal nanoparticle was five methylene
units to decrease the quenching effect by the metal surface.14
To examine the dependence of the photochromic reactivity
of diarylethene 1a on the core size of the nanoparticle, differ-
ent sizes of the nanoparticles were prepared by changing the
molar ratio between metal source and ligand 1a.
Scheme 1 shows the synthetic route to diarylethene 1a.
Hydroxy-terminated diarylethene 4 was synthesized using
methoxymethyl protecting group. Bromoalkyl group was intro-
duced by Williamson ether synthesis, and the final alkanethiol
derivative 1a was synthesized by the reaction with hexameth-
yldisilathiane and tetrabutylammonium fluoride. The structure
of ligand 1a was confirmed by NMR, IR, and high-resolution
mass spectroscopy and elemental analysis.
Photochromism of Ligand 1a. Ligand 1a showed a photo-
chromic reaction in ethyl acetate by alternative irradiation with
313 and 578 nm light (Fig. 2). Upon irradiation with 313 nm
light, ligand 1a underwent a photochromic reaction in ethyl
acetate to give blue-purple solution. The blue-purple color is
due to the formation of the closed-ring isomer 1b. The absorp-
tion maximum was observed at 577 nm. The conversion under
irradiation with 313 nm light was 81%. Upon irradiation with
578 nm light, the colored solution turned colorless. The quan-
tum yield of the cyclization (313 nm) and cycloreversion
(517 nm) reactions were measured using 1,2-bis(benzothio-
phen-3-yl)hexafluorocyclopentene as a reference,15 and the
cyclization and cyclereversion quantum yields were deter-
mined to be 0.41 and 0.023, respectively.
Photochemical properties of photochromic dyes on the
surface of metal nanoparticles should also be affected by the
metal. Gold nanoparticles capped with azobenzene11 and spi-
ropyran12 have been prepared and their photochromic reactiv-
ity was examined. In this paper, in order to investigate the pho-
tochromic reactivity on metal nanoparticles in detail, diaryl-
ethene-capped gold and silver nanoparticles were prepared,
and the effect of the plasmon absorption on the photochromic
reactivity was studied.13
Published on the web September 5, 2006; doi:10.1246/bcsj.79.1413

1414 Bull. Chem. Soc. Jpn. Vol. 79, No. 9 (2006)
Photochromism of Metal Nanoparticles
F2
F2
F2
S
F2
S
F2
S
F2
S
UV
Vis.
O
SH
O
SH
1b
1a
UV
:
:
M
:M
Vis.
: 1a
: 1b
Au-1a
Ag-1a
Au-1b
Ag-1b
Fig. 1. Photochromic reactions of diarylethene 1 and Au– and Ag–1.
F2
1) n-BuLi
F2
F
F2
S
F2
F2
2)
F2
S
F2
S
F2
S
F2
S
Br
HCl
THF
S
THF
OMOM
OMOM
OH
(92%)
(79%)
2
3
4
F2
F2
F2
S
Si Si
F2
F2
S
F2
S
Br(CH2)5Br
Bu4NF
K2CO3
acetone
THF
S
S
O(CH2)5SH
O(CH2)5Br
(11%)
(80%)
5
1a
Scheme 1. Synthesis of ligand 1a.
ratio for preparing gold and silver nanoparticles were changed
as Au or Ag:1a = 1:1 and 3:1. Four kinds of nanoparticles,
Au–1a(1:1), Au–1a(3:1), Ag–1a(1:1), and Ag–1a(3:1) were
prepared with molar ratios of Au:1a = 1:1, Au:1a = 3:1,
Ag:1a = 1:1, and Ag:1a = 3:1, respectively. The nanoparti-
cles were soluble in chloroform, ethyl acetate, and toluene.
To measure the particle size, transmission electron micros-
copy (TEM) and dynamic light scattering (DLS) measure-
ments were performed. TEM samples were prepared by drop-
ping a toluene or ethyl acetate solution on a carbon-coated
copper grid. Figure 3 shows the TEM images of Au– and
Ag–1a. The size distribution of the particles is moderately
polydisperse. The particles are well separated from each other
due to the diarylethene monolayers. Figure 4 shows the histo-
grams of the diameter of gold and silver nanoparticles Au–
and Ag–1a based on TEM images. The average diameter of
Au–1a(1:1), Au–1a(3:1), Ag–1a(1:1), and Ag–1a(3:1) were
2:2 ꢁ 0:3, 3:2 ꢁ 0:4, 1:2 ꢁ 0:2, and 6:7 ꢁ 1:5 nm, respectively
(Table 1).
0.2
0.15
0.1
0.05
0
300
400
500
600
700
800
Wavelength / nm
Fig. 2. Photochromic reaction of ligand 1a in ethyl acetate
(6.5 mmol Lꢂ1). Dotted line denotes the open-ring isomer;
solid line denotes the closed-ring isomer; dashed line
denotes the spectrum in the photostationary state under
irradiation with 313 nm light.
Preparation and Characterization of Gold and Silver
Dynamic light scattering (DLS) measurements were also
carried out in ethyl acetate to get further information on the
particle size (Fig. 5). While TEM image reflects only diameter
of silver core, DLS measurement reflects Brownian movement
of silver core and diarylethene monolayer; therefore, the parti-
cle size measured by DLS was larger than that of TEM image.
The number-average diameter of Ag–1a(1:1) and Ag–1a(3:1)
Nanoparticle.
Gold nanoparticles capped with thiol 1a
(Au–1a) were prepared by the Brust and Schiffrin protocol.6
Silver nanoparticles (Ag–1a) were synthesized by Kim’s meth-
od which is a modification of the Brust’s protocol.16 Nanopar-
ticles of different sizes were prepared by changing the molar
ratio between diarylethene 1a and metal source. Stoichiometric

H. Yamaguchi et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 9 (2006) 1415
a)
b)
c)
d)
Fig. 3. TEM images of a) Au–1a(1:1), b) Au–1a(3:1), c) Ag–1a(1:1), and d) Ag–1a(3:1).
40
30
20
10
0
20
15
10
5
a)
b)
0
1.5
2.0
2.5
3.0
3.5
2.0
2.5
3.0
3.5
4.0
4.5
Diameter / nm
Diameter / nm
c) 50
40
d)
14
12
10
8
30
6
20
4
10
2
0
0
3.0
0.7
1.0
1.5
2.0
4.5
6.0
7.5
9.0 10.5
Diameter / nm
Diameter / nm
Fig. 4. Core size histograms of a) Au–1a(1:1), b) Au–1a(3:1), c) Ag–1a(1:1), and d) Ag–1a(3:1) obtained from the TEM images
(Figs. 3a–3d).
determined by DLS measurement were 3.6 and 9.0 nm, respec-
tively. This result agreed with the particle size difference ob-
served in TEM images.
In order to investigate the packing of the diarylethene mole-
cules on the metal nanoparticles, IR spectra of diarylethene-
capped gold and silver nanoparticles were measured. The spec-
tra of gold and silver nanoparticles are similar to that of ligand
1a itself, indicating that diarylethenes definitely capped the
gold and silver nanoparticles. The spectrum of ligand 1a has
peaks at 2864 and 2935 cmꢂ1 originating from alkyl C–H
asymmetric and symmetric stretching mode, respectively. On
the other hand, Au–1a(1:1), Au–1a(3:1), Ag–1a(1:1), and
Ag–1a(3:1) have peaks at 2852–2857 and 2921–2928 cmꢂ1
.
The shift to lower wavenumber suggests that diarylethenes
on the metal nanoparticles adopted on all-trans conformation
and were packed more regularly than free 1a.17

1416 Bull. Chem. Soc. Jpn. Vol. 79, No. 9 (2006)
Photochromism of Metal Nanoparticles
Table 1. Diameters and Optical Properties of Gold and Silver Nanoparticles Capped with Diarylethene 1
Plasmon
absorption
Absorption maxima of the
closed-ring isomer ꢀmax
/nmaÞ
TEM
(Diameter/nm)
DLS
(Diameter/nm)
Entry
IR stretching/cmꢂ1
ꢀ
max/nm
1
N/A
N/A
N/A
N/A
3.6
9.0
N/A
N/A
N/A
520
520
none
435
520
422
577
578
582
573
574
582
573
2864, 2935
2852, 2921
2856, 2926
2855, 2926
2857, 2928
N/A
Au–1a(1:1)
Au–1a(3:1)
Ag–1a(1:1)
Ag–1a(3:1)
Au–1b0
2:2 ꢁ 0:3bÞ
3:2 ꢁ 0:4
1:2 ꢁ 0:2
6:7 ꢁ 1:5
2:9 ꢁ 0:7
11:4 ꢁ 3:6
Ag–1b0
N/A
a) Measured by subtracting the spectra before and after irradiation. b) The value in Ref. 13 is revised.
a)
b)
40
30
20
10
0
40
30
20
10
0
1
10
100
1000
1
10
100
1000
Diameter / nm
Diameter / nm
Fig. 5. DLS histograms of a) Ag–1a(1:1) and b) Ag–1a(3:1).
a)
b)
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1.0
0.8
0.6
0.4
0.2
0
300
400
500
600
700
800
300
400
500
600
700
800
Wavelength / nm
Wavelength / nm
c)
d)
0.3
0.2
0.1
0
0.3
0.2
0.1
0
300
400
500
600
700
800
300
400
500
600
700
800
Wavelength / nm
Wavelength / nm
Fig. 6. Absorption spectra of a) Au–1a(1:1), b) Au–1a(3:1), c) Ag–1a(1:1), and d) Ag–1a(3:1) in ethyl acetate. Solid lines denote
the open-ring isomer. Dotted lines denote the photostationary state under irradiation with 313 nm light.
Photochromism of Gold and Silver Nanoparticle. All of
the metal nanoparticles capped with diarylethenes underwent
photochromic reactions by irradiation with UV and visible
light in ethyl acetate (Fig. 6). The red-brown solution of gold
nanoparticles Au–1a turned red-purple upon irradiation with
313 nm light, which is due to the formation of the closed-ring

H. Yamaguchi et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 9 (2006) 1417
a)
b)
1
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.5
0.4
0.3
0.2
0.1
0
0.15
0.1
0.05
0
0.8
0.6
0.4
0.2
0
450
500
550
600
650 700
Wavelength / nm
450
500
550
600
650
700
Wavelength / nm
300
400
500
600
700
800
300
400
500
600
700
800
Wavelength / nm
Wavelength / nm
Fig. 7. Absorption spectra of a) Au–1b0 and b) Ag–1b0 in ethyl acetate: the open-ring isomer (solid line); the closed-ring isomer
(dashed line); in the photostationary state under irradiation with 313 nm light (dotted line). Inset shows expansion from 450 to
700 nm.
isomer. For silver nanoparticles Ag–1a, the color changed
from pale brownish yellow to greenish yellow. In both cases,
the solution returned back to original color after irradiation
with 578 nm light. Although Ag–1a(3:1) has a strong plasmon
absorption peak at 435 nm, the sample underwent a photochro-
mic reaction.
64%). Many fluorophores are reported to lose the fluorescent
properties on the surfaces of metal nanoparticles.19 However,
the cyclization reaction of diarylethenes (<10 ps) is a much
faster phenomenon than fluorescence (ꢃca. several ns). This
fast reaction is the main reason why the photochromic reaction
took place on the surface of noble metal nanoparticles.
The optical properties of the gold and silver nanoparticles
capped with diarylethenes are summarized in Table 1. The
plasmon absorption intensity decreases when the particles size
becomes small. Ag–1a(1:1) did not show any distinctive plas-
mon absorption because the size of this nanoparticle was very
small.7 The absorption maxima of the closed-ring isomer was
not strongly dependent on the metal element nor the particle
size.
Gold and silver nanoparticles were prepared using the
closed-ring isomer 1b. By this method, nanoparticles capped
with only the closed-ring isomers (Au–1b0 and Ag–1b0) were
prepared. The closed-ring isomer was separated by HPLC from
a mixture of the closed- and the open-ring isomer, and the
preparation of the nanoparticle was performed in the dark.
The size distributions of the nanoparticles are listed in Table 1.
Figure 7 shows the photochromic behavior of Au– and Ag–
1b0. The conversion was estimated as 74 and 64% for gold
and silver nanoparticles, respectively. The conversion gives
information concerning the ratio of the cyclization and the
cycloreversion quantum yields,18 and the lower conversion
as compared to that of the free ligand indicates that the cycli-
zation quantum yield is suppressed due to the metal. Although
the conversion was suppressed by the metal, it was proved
in this study that a photochromic reaction takes place on the
surface of noble metal nanoparticles.
Conclusion
Gold and silver nanoparticles capped with diarylethene were
synthesized by Brust and Kim’s method. The particle sizes of
gold and silver nanoparticles were determined by TEM and
DLS measurement, and from the IR spectra diarylethene cap-
ped the gold and silver nanoparticles and were densely packed.
The metal nanoparticles underwent photochromic reactions by
irradiation with UV and visible light. Although the quenching
of the cyclization reaction was observed, the photochromic
reaction of diarylethene occurred reversibly on the gold and
silver nanoparticles.
Experimental
Materials. IR spectra were recorded on a Perkin-Elmer Spec-
trum One instrument by ATR method. 1H NMR spectra were
recorded on Varian Gemini 200 instruments. UV–vis spectra were
recorded on a Hitachi U-3500 spectrophotometer. Mass spectra
were obtained on JEOL JMS-GCmate II. Melting points were
not corrected.
All reactions were monitored by thin-layer chromatography
carried out on 0.2-mm E. Merck silica-gel plates (60F-254).
Column chromatography was performed using silica gel (Kanto,
63-210 mesh).
1-[5-(4-Methoxymethoxyphenyl)-2,4-dimethyl-3-thienyl]-2-
(2,4-dimethyl-5-phenyl-3-thienyl)hexafluorocyclopentene (3):
To a solution of 3-bromo-5-(4-methoxymethoxyphenyl)-2,4-di-
methylthiophene (2)20 (4.32 g, 16 mmol) in dry THF (45 mL) was
added 1.6 M n-BuLi (11 mL, 17.6 mmol) at ꢂ70 ꢄC. After the mix-
ture was stirred for 1 h, a solution of 1-(2,4-dimethyl-5-phenyl-3-
thienyl)heptafluorocyclopentene21 (1.05 g, 2.76 mmol) in dry THF
(8 mL) was added. The reaction mixture was stirred at ꢂ70 ꢄC for
2 h, and then the solution was allowed to warm up to room temper-
ature, quenched by water, extracted with ether, washed with brine,
dried over MgSO4, and concentrated. Purification by column chro-
matography (silica, hexane:CHCl3 = 9:1) gave diarylethene de-
The photochromic reactivity revealed that the cyclization
reaction was more effectively quenched than the cyclorever-
sion reaction. In the case of Ag–1a(3:1) and Ag–1b0, a strong
plasmon band was observed between the absorption maxima of
the open- and the closed-ring isomer. Provided that quenching
occurs by an energy-transfer mechanism, the cyclization reac-
tion should be quenched more effectively than the cyclorever-
sion reaction. The gold nanoparticles have a plasmon band at a
longer wavelength than silver nanoparticles, which can explain
the stronger quenching by the silver nanoparticles (74% vs

1418 Bull. Chem. Soc. Jpn. Vol. 79, No. 9 (2006)
Photochromism of Metal Nanoparticles
rivative 3 (1.20 g, 79%) as a brown wax. 1H NMR (CDCl3, 200
MHz) ꢁ 2.00–2.11 (m, 6H), 2.28–2.38 (m, 6H), 3.49 (s, 3H), 5.20
(s, 2H), 7.05 (d, 2H, J ¼ 8:6 Hz), 7.22–7.44 (m, 7H). MS(FAB)
(m=z) [M]þ 608. Anal. Calcd for C31H26F6O2S2: C, 61.31; H,
4.33%. Found: C, 61.17; H, 4.31%.
the organic layer was separated and concentrated. The toluene
(3 mL) solution of the residue was added to ethanol (20 mL) and
centrifuged (0 ꢄC, 6000 rpm, 40 min). The precipitate was collect-
ed, redissolved in toluene and ethanol, sonicated, and centrifuged
again. This cycle was repeated three times, and the precipitate was
finally dried in vacuo. Au–1a was obtained as a black powder.
Nanoparticles of different sizes were prepared by similar method
by changing the molar ratio between HAuCl4 and 1a to 3:1. IR
(Ge ATR) 2921, 2851, 1608, 1514, 1342, 1274, 1259, 1145, 1112,
1055, 988 cmꢂ1; UV–vis (toluene) ꢀmax 515 (sh) nm.
1-[5-(4-Hydroxyphenyl)-2,4-dimethyl-3-thienyl]-2-(2,4-di-
methyl-5-phenyl-3-thienyl)hexafluorocyclopentene (4): To a
solution of derivative 3 (2.2 g, 3.61 mmol) in THF (40 mL) was
added conc. HCl (9.2 mL) and stirred for 6.5 h. After the addition
of water, the mixture was extracted with ether, washed with brine,
dried over MgSO4, and concentrated. Purification by column chro-
matography (silica, CHCl3) gave phenol derivative 4 (1.88 g,
92%) as a green wax. 1H NMR (CDCl3, 200 MHz) ꢁ 2.04–2.10
(m, 6H), 2.32–2.38 (m, 6H), 4.85 (s, 1H), 6.85 (d, 2H, J ¼ 8:0
Hz), 7.21–7.40 (m, 7H). MS(FAB) (m=z) [M]þ 564. Anal. Calcd
for C29H22F6OS2: C, 61.33; H, 4.04%. Found: C, 61.69; H, 3.93%.
1-[5-(4-Bromopentyloxyphenyl)-2,4-dimethyl-3-thienyl]-2-
(2,4-dimethyl-5-phenyl-3-thienyl)hexafluorocyclopentene (5):
To a solution of derivative 4 (1.11 g, 1.97 mmol) in acetone
(30 mL) was added K2CO3 (0.27 g, 1.97 mmol) and 1,5-dibromo-
pentane (0.53 mL, 3.94 mmol). After the mixture was refluxed un-
der argon atmosphere K2CO3, it was filtrated and then concentrat-
ed. After the addition of water, the mixture was extracted with
ether, washed with brine, dried over MgSO4, and concentrated.
Purification by column chromatography (silica, CHCl3) gave bro-
moalkane derivative 5 (1.13 g, 80%) as a yellow wax. 1H NMR
(CDCl3, 200 MHz) ꢁ 1.58–2.00 (m, 6H), 2.00–2.22 (m, 6H), 2.24–
2.46 (m, 6H), 3.45 (t, 2H, J ¼ 6:6 Hz), 3.99 (t, 2H, J ¼ 6:2 Hz),
6.90 (d, 2H, J ¼ 9 Hz), 7.20–7.42 (m, 7H). MS(FAB) (m=z) [M]þ
712. Anal. Calcd for C34H31BrF6OS2: C, 57.46; H, 4.43%. Found:
C, 57.22; H, 4.38%.
Silver Nanoparticles Capped with Thiol 1a (Ag–1a(1:1)): A
solution of tetraoctylammonium bromide (73 mg, 0.13 mmol) in
chloroform (5 mL) was added to a solution of AgNO3 (5.1 mg,
0.03 mmol) in ultrapure water (18.2 Mꢀ cm, 1 mL), and then, the
solution was stirred vigorously for 1 h. Then, a solution of ligand
1a (20 mg, 0.03 mmol) in chloroform (2 mL) was added. In a sep-
arate flask, a solution of NaBH4 (13 mg, 0.34 mmol) in ultrapure
water (18.2 Mꢀ cm, 1 mL) was placed, and then, it was slowly
added to reaction vessel. After stirring for 3 h, the aqueous phase
was removed and the organic phase was concentrated. The residue
was dissolved in a small amount of chloroform and poured into
ethanol (30 mL) and then, the precipitated particles were collected
by filtration. The precipitate was again dissolved in small amount
of chloroform and poured into ethanol, and then the precipitated
particles were collected by filtration. This cycle was repeated us-
ing methanol and hexane to remove excess thiol and phase trans-
fer reagent. Ag–1a(1:1) was obtained as a black powder. Nanopar-
ticles of different sizes were prepared by changing the molar ratio
between AgNO3 and ligand 1a to 3:1. The silver nanoparticles can
be dissolved in chloroform, ethyl acetate, and toluene. IR (Ge
ATR) 2926, 2855, 1607, 1514, 1471, 1444, 1341, 1275, 1249,
1-{5-[4-(5-Mercaptopentyloxy)phenyl]-2,4-dimethyl-3-thi-
enyl}-2-(2,4-dimethyl-5-phenyl-3-thienyl)hexafluorocyclopen-
tene (1a): To a solution of derivative 5 (200 mg, 0.28 mmol) in
THF (0.56 mL) was added a mixture of hexamethyldisilathiane
(142 mL, 0.672 mmol, 2.4 equiv) and tetrabutylammonium fluoride
(178 mL, 0.616 mmol, 2.2 equiv). After the mixture was stirred for
2 days at room temperature, water was poured into the reaction
vessel. The mixture was extracted with CH2Cl2, washed with
aqueous NH4Cl and brine, dried over MgSO4, and concentrated.
Purification by column chromatography (silica, hexane:CHCl3 =
2:1) and then GPC (CHCl3) and HPLC (Kanto chemical mightysil
Si60 250-20, hexane:EtOAc = 9:1) gave thiol 1a (20 mg, 11%) as
a blue wax. 1H NMR (CDCl3, 200 MHz) ꢁ 1.35 (t, 1H, J ¼ 7:8
Hz), 1.50–1.90 (m, 6H), 2.02–2.10 (m, 6H), 2.30–2.36 (m, 6H),
2.57 (q, 2H, J ¼ 6:8 Hz), 3.98 (t, 2H, J ¼ 6:4 Hz), 6.89 (d, 2H,
J ¼ 8:8 Hz), 7.26 (d, 2H, J ¼ 8:6 Hz), 7.29–7.42 (m, 5H); IR (Ge
ATR) 2935, 1608, 1514, 1341, 1275, 1248, 1145, 1114, 1056, 988
cmꢂ1; UV–vis (EtOAc) ꢀmax ("/Mꢂ1 cmꢂ1) 274 (2:9 ꢅ 104) nm,
closed-ring isomer 1b 577 (1:2 ꢅ 104) nm; HRMS (FAB) (m=z)
[M]þ calcd for C34H32F6OS3: 666.1528. Found 666.1519. Anal.
Calcd for C34H32F6OS3: C, 61.36; H, 4.99%. Found: C, 61.24;
H, 4.84%.
Preparation of Metal Nanoparticles. Gold Nanoparticles
Capped with Thiol 1a (Au–1a(1:1)): A solution of hydrogen
tetrachloroaurate(III) hydrate (9 mg, 21.9 mmol) in ultrapure water
(18.2 Mꢀ cm, 0.76 mL) was added to a solution of tetraoctyl-
ammonium bromide (56 mg, 102 mmol) in toluene (5 mL) and
the mixture was vigorously stirred for 10 min. A solution of thiol
1a (16 mg, 24 mmol) in toluene (2 mL) was added to the mixture.
Then, a solution of sodium tetrahydroborate (9 mg, 230 mmol) in
water (0.58 mL) was slowly added to the mixture. After stirring,
1191, 1145, 1114, 1055, 1033, 988, 878, 859, 830, 758, 697 cmꢂ1
.
Photochemical Mesurement. Absorption spectra were mea-
sured on a spectrophotometer (Hitachi U-3500). Photoirradiation
was carried out using a USHIO 500 W super high-pressure mercu-
ry lamp or a USHIO 500 W xenon lamp. Mercury lines of 313 and
578 nm were isolated by passing the light through a combina-
tion of band-pass filter (UV-D33S) or sharp-cut filter (Y-50) and
monochromator (Ritsu MC-20L).
Condition for the separation of the closed-ring isomer 1b was
as follows. Pump: Hitachi L-2420; Detector: Hitachi L-2130 (de-
tective wavelength: 313 nm); Column: Mightysil (Kanto Chemical
Co., Inc.) 250–4.6 mm; Eluent:hexane:CH2Cl2 = 3:1.
TEM Measurement. TEM measurement was performed on a
Hitachi H-7500 instrument. The measurement was performed at
100 kV. TEM samples were prepared by placing a drop of ethyl
acetate or toluene solution of Au– and Ag–1a onto carbon-coated
copper grid.
DLS Measurement. Particle size distribution was measured
on Malvern Zetasizer Nano-ZS particle sizer equipped with
633 nm laser as light source, using a fixed angle (173ꢄ). The sam-
ples were filtered by using a MILLIPORE Millex membrane filter
(0.20 mm) before measurement. The samples were kept 25 ꢄC dur-
ing measurement.
This work was supported by PRESTO, JST and a Grant-in-
Aid for Scientific Research (S) (No. 15105006) from Japan
Society of the Promotion of Science.
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