COMMUNICATION
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Prussian blue nanoparticles protected by the water-soluble p-conjugated
polymer PEDOT-S: synthesis and multiple-color pH-sensing with
a redox reactionw
Mami Yamada,*ab Naoto Ohnishi, Makoto Watanabe and Yasuko Hino
c
d
a
Received (in Cambridge, UK) 26th August 2009, Accepted 6th October 2009
First published as an Advance Article on the web 16th October 2009
DOI: 10.1039/b917552k
Prussian blue nanoparticles (PB NPs), stabilized for the first
(PEDOT-S; Fig. 1). PEDOT-S was recently used in an electro-
luminescence device or a solar cell due to its high conductivity
with high transparency and excellent stability in its doped
time by the p-conjugated polymer poly(4-(2,3-dihydrothieno-
[
3,4-b][1,4]dioxin-2yl-methoxy-1-butanesulfonic acid, potassium
9
salt) (PEDOT-S), demonstrated a novel multiple-color pH-
sensing function with a redox reaction based on the electronic
interaction between the PB nano-core and the PEDOT-S shell.
state. We demonstrate that an ‘‘anionic’’ pendant group of
sulfonates in PEDOT-S presents effective surface protection
from Fe cations to PB NPs, compared to the protection
provided by previously used nonionic or cationic polymers.
Further, PEDOT-S-surrounded PB NPs (PEDOT-S/PB NPs)
provide a novel multiple-color pH-sensing function with a
redox reaction based on the electronic interaction between the
PB nano-core and the PEDOT-S shell.
The science of metal organic frameworks (MOFs) is attractive
because of the versatile properties of MOFs, which depend on
their crystal structure using different organic ligand and metal
1
ions. Among these MOFs, Prussian blue and its analogues
III
II
0
(
PBs), generally formulated as
A
0
2x
M
(1.5ꢀx)[M (CN)
x = 0–1; A = alkali metal ion; M, M = transition metal ions),
6
]
n w w n
PEDOT-S (M = 91700, M = 10400, M /M = 1.14) was
(
synthesized in eight steps, using a monomer of potassium
are some of the most widely known MOFs with a face centered
2
cubic (fcc) structure. PBs are promising organic–inorganic
4-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)methoxybutane-1-
10
sulfonate (EDOT-S) (for detailed experimental techniques
hybrid materials that exhibit interesting characteristics, such
and measurements, see the ESIw). PEDOT-S/PB NPs were
obtained as follows: 10 mL of an aqueous mixture of 4.5 mM
3
as photo-induced magnetization, electrochromism, pressure
4
5
6
tuning, and biosensing. As the next stage, preparation of PBs
as ‘‘nano’’-materials would enable their application in growing
new nanodevices, and has been investigated using several
FeCl
calculated per one monomer molecule) was added to 10 mL
of 3.0 mM aqueous K [Fe(CN) ] with vigorous stirring for
2
ꢁ6H
2
O and 7.5 mM PEDOT-S (the concentration is
3
6
7
techniques. The simplest way is to crystallize PBs in a
24 h. The resulting blue solution was poured into B20 mL of
methanol. The precipitate was filtered using a membrane,
washed with methanol three times, and dried overnight in
air at room temperature to yield powdery PEDOT-S/PB NPs
quantitatively.
dilute solution containing an organic polymer to give polymer-
stabilized PB nanoparticles (NPs). However, the problem to be
urgently solved is that the range of polymers used up to now
has been extremely limited, including for example, nonionic
7
c,d
(
poly(vinylpyrrolidone); PVP)
and cationic (poly(diallyl-
7
The X-ray diffraction (XRD) pattern of the obtained
compound exhibited an fcc crystal structure with the main peaks
at 17.521 (200), 24.641 (220), 35.321 (400) and 39.601 (420)
e
dimethylammonium chloride; PDDA) polymers. Expanding
polymer variation is a vital challenge for wider applications of
8
7e
PB NPs.
(Fig. S1w), suggesting the formation of PB crystals.
PEDOT-S/PB NPs easily redissolved in water to give a
This communication reports the first synthesis of
‘‘p-conjugated’’ polymer-stabilized PB NPs. The p-conjugated
polymer chosen here is poly(4-(2,3-dihydrothieno[3,4-b][1,4]-
transparent blue solution without any precipitates (Fig. S2aw).
dioxin-2yl-methoxy-1-butanesulfonic acid, potassium salt)
a
Department of Applied Chemistry, Tokyo University of Agriculture
and Technology (TAT), 2-24-16, Nakacho, Koganei,
Tokyo 184-8588, Japan. E-mail: m-yamada@cc.tuat.ac.jp;
Fax: +81-42-388-7379; Tel: +81-42-388-7379
PRESTO/Japan Science and Technology Agency (JST),
4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan
Sumitomo 3M Limited, 3-8-8, Minami Hashimoto, Sagamihara,
Kanagawa 229-1185, Japan
JSPS Research Fellowship, Laboratory of Silviculture and Forest
Ecology, Research Faculty of Agriculture, Hokkaido University,
Sapporo, Hokkaido 060-8589, Japan
b
c
d
w Electronic supplementary information (ESI) available: Experimental
details and additional results for XRD, UV-Vis, FT-IR, CV, and film
formation for PEDOT-S/PB NPs, photographs of PEDOT-S as a
function of pH, and the referenced experimental photograph for
PVP-stabilized PB NPs. See DOI: 10.1039/b917552k
Fig. 1 (Left) Illustration and (right) TEM image of the prepared
Prussian blue nanoparticles protected by the water-soluble
p-conjugated polymer PEDOT-S (PEDOT-S/PB NPs).
This journal is ꢂc The Royal Society of Chemistry 2009
Chem. Commun., 2009, 7203–7205 | 7203