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JAPAN NANONET BULLETIN
-- 79th Issue -- September 14, 2006
Nanotechnology Researchers Network Center of Japan
Ministry of Education, Culture, Sports, Science and Technology (MEXT)
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IN THIS ISSUE
Nanonet Interview:
"Expanding world of nanocarbon materials through molecular
transformation -- Approach from organic chemistry --"
Takeshi AKASAKA, Professor, Center for Tsukuba Advanced Research
Alliance and Graduate School of Pure and Applied Science, University
of Tsukuba
Young Researchers' Introduction:
"Creation of organic-inorganic ordered structures and their novel
functional properties"
Yuko TAKEOKA, Lecturer, Department of Chemistry, Sophia
University
-- NANO CALENDAR --
For information on nanotechnology related symposiums and conferences
held in the world,
http://www.nanonet.go.jp/english/calendar/
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NANONET INTERVIEW
Expanding world of nanocarbon materials through molecular
transformation -- Approach from organic chemistry --
(Issued in Japanese on March 23, 2005)
Takeshi AKASAKA, Professor, Center for Tsukuba Advanced Research
Alliance and Graduate School of Pure and Applied Science, University
of Tsukuba
Fullerene was discovered by Prof. Harold Kroto and his team in 1985.
Prof. Akasaka says, "A sufficient amount of fullerene became available
for organic chemical researchers' studies in the late 1990s. What
impressed me most about fullerene was that the material dissolved in an
organic solvent and that the solution became purple. When I saw this
phenomenon, I thought that chemists like me would be able to handle
fullerene like dye."
At that time, Prof. Akasaka was studying oxygen in air and its
photochemical reaction. Oxygen molecules do not react with organic
compounds under normal conditions because the electronic state of
oxygen in air is the triplet state, while that of organic compounds is
the singlet state. The molecules could react with organic compounds
through the use of dye that helps light energy excite electrons of
oxygen molecules to the reactive singlet state. Like dye, fullerene was
found to have the photosensitization action to excite triplet oxygen to
singlet one with visible light. "Like oxygen, fullerene was found to
have an electronic property to take in electrons. In other words,
fullerene with an atomic mass number of 720 was expected to have the
same reactivity as O2 from the viewpoint of organic chemistry," Prof.
Akasaka says. After the discovery, he started applying chemical
techniques used for oxygen to fullerene.
Prof. Akasaka thinks that many types of fullerene with an innumerable
variety of properties could be made by attaching various molecules to
C60 because the properties of the molecules would be added to the
original properties of fullerene. For example, fullerene derivatives
can be made from fullerene oxide through attachment of various types of
chemical compounds. He researched the possibility of a wide variety of
chemical modifications of fullerene, based on his oxygen studies. He
used silicon because the element is not only chemically stable but also
widely available. When photo-excited C60 was reacted with disilirane,
an organic silicon derivative C60(Mes4Si2CH2) was synthesized in high
yields, due to the addition reaction between the Si-Si sigma-bond and
the excited triplet state of C60. Prof. Akasaka studied the properties
of organic silicon derivatives systematically by searching for new
derivatives. Fullerene was found to have its electron-releasing ability
raised through its bond with silicon, which has high electron-
releasing ability. He says, "The fullerene with the highest electron-
releasing ability ever found is C60(SitBuPh2)4, which my team produced
by attaching four silicon atoms to C60. We are now confident that we
can forecast 80-90% of all synthetic processes and compounds used for
making types of fullerene that can meet required properties, and that
we can make such fullerene based on our forecast."
If chemistry to attach chemical compounds to fullerene is called
"reactive chemistry on the outer surface of fullerene," then "chemistry
inside the fullerene cage" deals with metallo-fullerene. Prof. Akasaka
says, "Nothing exists inside a fullerene cage comprised of 60 carbon
atoms. As far as I know, a real vacuum exists only inside the fullerene
cage. So, I imaged what would happen if something were put inside the
fullerene cage." In the nitrogen or inert gas-containing fullerene, the
fullerene cage does not interact with the gas atoms in it. The
electronic state of fullerene changes significantly when it contains
Group II, III or IV metal elements because electrons are transferred
from the metal atoms with high electron-releasing ability to the
fullerene. He confirmed in NMR (nuclear magnetic resonance)
measurements that two lanthanum atoms circulated inside a cage of
fullerene C80 at a high speed at room temperature. C80 has seven types
of isomers that meet the isolated pentagon rule, which states that a
five-membered ring is always surrounded by six-membered rings. The most
symmetrical isomer among the seven is thought to become stable when it
contains two lanthanum atoms as La2@C80. The lanthanum atoms become
stable at minimum points of electrostatic potential inside the isomer
because they are charged positively after they release electrons to the
isomer. In the case of Sc@C82, which contains a single scandium atom in
a C82 cage, the atom is localized at the minimum point of electrostatic
potential just under a six-membered ring. However, in the case of
La2@C80, the La atoms circulate three-dimensionally because the minimum
points of electrostatic potential exist along the inner surface of the
C80 cage and the La atoms are not localized. This indicates the
possibility that three-dimensional circulations of the La atoms could
be changed to two-dimensional circulations by controlling the
electrostatic potential inside the fullerene through chemical
modification. Prof. Akasaka actually clarified that the La atoms
circulate two-dimensionally along an equator by attaching disilirane to
the north pole of the C80 cage.
Prof. Akasaka has also started studying single-walled carbon nanotubes
(SWNTs). He says, "Carbon nanotubes dissolve in neither water nor
solvent. Chemists usually handle substances dissolved in solution.
Carbon nanotubes do not appear to be covered in chemistry. However,
chemists could handle them if the tubes were dispersed in solution." To
disperse SWNTs, detergent, pi-conjugated molecules, porphyrin, DNA or
other polymers are used. In this method, removal of dispersant is very
difficult. Prof. Akasaka succeeded in dispersing SWNTs by using a
tetrahydrofuran solution containing amine, which can be removed
relatively easily. "What is attracting researchers' attention most is
SWNT's metallic and semiconducting properties," he says.
Prof. Akasaka has also succeeded in isolating metallic or
semiconducting SWNTs through centrifugation of dispersion liquid. He
says, "Nanoscience is essential for the foundation of nanotechnology.
As science advances, some of its results can be applied to technology.
I think now is the time when the science of nanotubes is advancing by
leaps and bounds."
(Interviewer: Kuniko Ishiguro, Cosmopia Inc.)
For more information including figures,
http://www.nanonet.go.jp/english/mailmag/2006/079a.html
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YOUNG RESEARCHERS' INTRODUCTION
Creation of organic-inorganic ordered structures and their novel
functional properties
(Issued in Japanese: August 24, 2005)
Yuko TAKEOKA, Lecturer, Department of Chemistry, Sophia
University
The purpose of this study is to build novel organic-inorganic
semiconductor heterostructures with strong nonlinear optical properties
and functionality. It is thought that a hybrid exciton can be formed
at the interface between layers in organic-inorganic semiconductor
heterostructures due to resonant mixing of different exciton states in
each layer, which have excitons and exhibit strong nonlinear optical
properties. In order to develop a hybrid exciton, we have focused on
organic-inorganic layered perovskite-type compounds.
Layered perovskites with the general formula (RNH3)2PbX4 naturally form
a quantum-well structure consisting of a lead halide semiconductor
sheet sandwiched between organic insulator layers (Figure 1). Because
the insulating organic layers have a wide band gap, excitons are
confined in the inorganic [PbX6]^(4-) layers, and these layers
contribute to strong photoluminescence with high optical nonlinearity,
which are characteristics that have potential applications in optical
devices. Organic materials with specific functionality have been
combined on a molecular scale with an inorganic matrix, having other
target properties, to create an organic-inorganic composite, which has
useful properties or which has new phenomena that arise from the
interactions between the organic and inorganic components.
In this study, we have tried to incorporate pi-conjugated systems, such
as polydiacetylene, fullerene, and pi-conjugated oligomers, into the
organic-inorganic perovskites, and the optical properties of these new
heterostructures have been investigated.
For more information including figures,
http://www.nanonet.go.jp/english/mailmag/2006/079b.html
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