Outline of Research
Molecular aggregates: Materials Chemistry Group
We are aiming at elucidation of the
correlation between structures and properties in mainly organic molecular
solids. On the basis of knowledge of thus-obtained structure-property
correlation and a variety of information on materials science, we are also
aiming at creation of condensed molecular systems which are expected to show
salient characteristics and/or remarkable functions in terms of electronic
properties.
In short, our target is to clarify
the electronic structure of aggregates of particular molecules with notable
characteristics in relation to their aggregation structures, in order to
construct molecular assemblies show novel electronic properties and/or
functions.
Our research field is therefore
involved in materials science in a wide sense and corresponds to organic
solid-state chemistry in a narrow sense. Our studies are carried out chiefly
from a standpoint of physical chemistry and partly from those of organic
chemistry and coordination chemistry, which means that our field is more or less
interdisciplinary. Besides, we sometimes submit our research reports to the
journals with their names including ephysical chemistry,f echemical physics,f
ematerials chemistry,f or esurface science.f
Our research title is eelectronic
properties of organic molecular solids.f We carry out fundamental research to
contribute to the elucidation of their electronic properties in terms of the
correlation between their aggregation forms and electronic structures and to the
creation of molecular systems with novel electronic functions, with laying
stress on the analysis of their electronic structures.
We are interested in organic compounds,
metal complexes and also polymers in the solid state; here eorganic
semiconductorf should be a keyword. The subjects of our studies are their
crystals as well as, in particular, their thin films having a high probability
of controlled molecular aggregation.
Electronic structures of the states in such
solids both just below the energy gap and just above the energy gap play an
absolutely important role in the expression of electronic properties involving
behavior of photons and electrons in them. In consideration of the results
obtained from both analysis of electronic structures in those energy regions
using photoemission spectroscopies and observation of molecular aggregation
forms with diffraction and spectroscopic methods, we investigate electronic
properties characteristic of the materials of our interest.
With centering these analytical studies in
our research activities, we also proceed synthetic studies aiming at new
functional molecules, novel molecular assemblies, condensed molecular systems
expected to show unique dynamic behaviors, and so on.
Thus, we carry out not only analytical
studies but also synthetic studies in a wide sense with bearing in mind the
correlation among structures, electronic structures and electronic properties of
organic molecular aggregates. Our goal should be a discovery, understanding and
creation of molecular systems being attractive in terms of materials science.
1. Analyses of Electronic Structures in Organic Solids, Thin Films and their Surfaces and Interfaces
«Elucidation of characteristics and behaviors of electron systems in molecular solids, thin films and their interfaces»
Electronic structures of organic compounds, metal complexes and polymers in the
solid state, in particular, in thin films and/or at their interfaces, are
examined using ultraviolet photoemission spectroscopy (UPS) and/or inverse
photoemission spectroscopy (IPES). These measurements enabled us to directly
observe electronic structures around the energy gap in an object of research;
they lead to its characteristic electronic properties.
To our knowledge, there are only a few
laboratories where such unique studies on the basis of observation of extended
electronic structures are carried out now.
We are aiming at elucidation of the
correlation between the aggregation form in a molecular aggregate of interest
and its electronic structure in the solid state: the electronic structure is in
principle derived from the electronic structure of component molecules. Many
problems involving surfaces and interfaces of molecular thin films are also
issues of our concern, as they are not yet investigated extensively in spite of
their importance from both fundamental and practical points of view.
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Organic solids are generally bound by a weak intermolecular interaction,
however, particular molecular solids suffer from an additional interaction
leading to their unique electronic properties. The examination of such
interactions is also of our keen interests.
These studies are carried out using our
home-built apparatuses in most cases. As a matter of course it is indispensable
to develop and/or improve a methodology and/or an apparatus for the purpose of
acquisition of essentially new and important information necessary for those
studies. Accordingly, we are struggling to promote this kind of projects.
· Elucidation of molecular energy relaxation in organic solids
· Direct observation of unoccupied electronic states in organic semiconductors
· Study of the correlation between molecular aggregation forms and extended electronic structures in organic solids or thin films
· Understanding of a behavior of the extended electronic structure due to the charge carrier injection in an organic semiconductor
· Direct
examination of behaviors of electron levels at the interfaces of organic thin
films
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· Unoccupied electronic states in a hexatriacontane thin film studied by inverse photoemission spectroscopy, K. Tsutsumi, H. Yoshida and N. Sato, Chem. Phys. Lett. 361 (2002) 367–373.
· Unoccupied electronic states of 3d-transition metal phthalocyanines (MPc: M = Mn, Fe, Co, Ni, Cu and Zn) studied by inverse photoemission spectroscopy, H. Yoshida, K. Tsutsumi and N. Sato, J. Elect. Spectrosc. Relat. Phenom. 121 (2001) 83-91.
· Unoccupied electronic structure in organic thin films studied by inverse photoemission spectroscopy, N. Sato, H. Yoshida and K. Tsutsumi, J. Mater. Chem. 10 (2000) 85-89.
· Energy shift for core electron levels of chemisorbed molecules observed by X-ray photoelectron spectroscopy in the course of monolayer growth on a Si(111) surface, M. Mitsuya and N. Sato, Langmuir 15 (1999) 2099-2102.
· Photoemission and inverse photoemission studies on a thin film of N,Nf-dimethylperylene-3,4,9,10-bis(dicarboximide), N. Sato, H. Yoshida and K. Tsutsumi, J. Elect. Spectrosc. Relat. Phenom. 88-91 (1998) 861-865.
· Molecular electronic relaxation in organic solids, N. Sato, Electrical and related properties of organic solids, R. W. Munn, A. Miniewicz and B. Kuchta (eds.), (Kluwer Academic Publishers, Dordrecht, 1997), pp. 157-166.
· Valence electronic structure at the interface of organic thin films, N. Sato and M. Yoshikawa, J. Elect. Spectrosc. Relat. Phenom. 78 (1996) 387-390.
· Characteristic electronic structures of organic solids classified in terms of molecular electronic relaxation, N. Sato, Synth. Metals 64 (1994) 133-139.
· Linearly condensed polythiophenes: Characteristic molecular aggregation of thieno[2h,3h: 4f,5f]thieno[2f,3f-d]thieno[3,2-b]thienophene crystals revealed by ultraviolet photoelectron spectroscopy, N. Sato, Y. Mazaki, K. Kobayashi and T. Kobayashi, J. Chem. Soc. Perkin Trans. 2 (1992) 765-770.
· Threshold ionization energy of C60 in the solid state, N. Sato, Y. Saito and H. Shinohara, Chem. Phys. 162 (1992) 433-438.
·
The electronic structure of poly(p-phenylenevinylene),
N. Sato, M. Lögdlund, R. Lazzaroni, W. R. Salaneck, J.-L. Brédas, D. D. C.
Bradley, R. H. Friend and K. E. Ziemelis, Chem. Phys. 160 (1992) 299-306.
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2. Construction of Molecular Systems Expected to Show Novel Electronic Properties
«Creation of molecular assemblies with new electron systems»
To build
molecular aggregates to be expected to show notable electronic properties, we
design and synthesize a new molecule with considering its possible aggregation
forms beforehand and also try to control the arrangement of molecules known
already.
In particular, by designing and
synthesizing a molecule having a bonding and/or a structure to be unique in
terms of the electronic structure, or by choosing such a characteristic molecule
from known molecules, we are going to fabricate a new molecular system with a
novel aggregation structure. Thus, we are aiming at the creation of new
materials with unique structures to be realized by making use of the identities
of those molecules through intermolecular interactions.
For instance, a highly amphoteric and polar
molecule (HAPM) is designed as a molecule fabricated by the connection of an
electron-donating segment and an electron-accepting one with a quasi-delocalized p-electron
system. Such a molecule can be expected to show various aggregation forms in
the solid state, depending on the ratio of intramolecular and intermolecular
charge-transfer interactions. Some forms of the solids may characteristic
structures leading to notable electronic properties. In practice, we have
synthesized test molecules of HAPM and now study their physical and chemical
properties.
· Design, synthesis, molecular assembly and characterization of HAPM.
· Arrangements of metal complex molecules toward a molecular artificial lattice
· Design of a hybrid material with introduction of optical active molecules into ordered cavities in an inorganic matrix compound
· Development
of a cluster-beam deposition method for the preparation of novel organic thin
films
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· Molecular orbital calculations of nonlinear optical parameters for test molecules of a highly amphoteric and polar molecule (HAPM), N. Sato, T. Sakuma, H. Yoshida, E. A. Silinsh and A. J. Jurgis, Mol. Cryst. Liq. Cryst. 355 (2001) 319-329.
· Monolayer films of U-shaped molecules: suppression of the aggregation-induced second-harmonic generation of squaraine dyes by guest-host interactions, G. J. Ashwell, A. N. Dyer, A. Green, N. Sato and T. Sakuma, J. Mater. Chem. 10 (2000) 2473-2476.
· A molecular design towards a highly amphoteric and polar molecule (HAPM) to assemble novel organic solid-state structures, N. Sato, I. Kawamoto, T. Sakuma, E. A. Silinsh and A. J. Jurgis, Mol. Cryst. Liq. Cryst. 333 (1999) 243-258.
· Anomalous absorption spectra of highly oriented thin films of triphenothiaselenazine, I. Shirotani, Y. Inagaki, N. Sato and H. Nishi, Chem. Phys. Lett. 304 (1999) 299-302.
· Correlation of molecular orientations at the interface of organic double-layered thin films, M. Hasegawa and N. Sato, Mol. Cryst. Liq. Cryst. 296 (1997) 409-426.
· Structure and absorption spectra of thin films of triphenodithiazine, C18N2S2H10, Y. Inagaki, I. Shirotani, M. Konno, N. Sato and H. Nishi, Mol. Cryst. Liq. Cryst. 296 (1997) 397-407.
· Electrical properties of thin films of bis(1,2-benzoquinonedioximato)-platinum(II), Pt(bqd)2, I. Shirotani, K. Takeda, F. Onuma and N. Sato, Mol. Cryst. Liq. Cryst. 285 (1996) 119-124.
·
Electronic properties of evaporated
thin films of bis(1,2-benzoquinone-dioximato)metal(II), M(bqd)2 (M =
Ni, Pd and Pt), I. Shirotani, T. Kudo, N. Sato, H. Yamochi and G. Saito, J.
Mater. Chem. 5 (1995) 1357-1362.
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3. Elucidation of Organic Solid-State Reactions to be Connected with Dynamic Electronic Properties
«Elucidation of dynamic behaviors of electron systems in relation to the manifestation or the control of particular properties»
We are
searching organic solid-state reactions to be connected with the manifestation
of novel electronic properties in the solid sate or the control of those
properties.
In this project, we are interested in the
transfer reactions of protons or ions, in relation to tautomerism,
rearrangement, addition or polymerization induced by illumination and/or heating
in the solid sate. Then we start with the solution of those reaction
mechanisms.
For example, we have been curious about a
thermal isomerization reaction: the reaction formula is as follows:
However, this reaction occurs not in the liquid solution mostly but in the solid state chiefly. How can we understand this fact? As a result of our studies, it turns out that the molecular arrangements in the crystal realize the reaction as shown here:
· Intra- and Inter-molecular rearrangement reactions of methyl cations in a methyl 4-(dimethyl-amino)benzenesulfonate crystal
· Proton behaviors in the hydrogen bonding system in a crystal of squaric acid derivative compounds
· Reversible photooxygenation reaction of a polycyclic aromatic hydrocarbon
· Controlled meso-phase polymerization of diacetylene molecules
· Proton relay in a one-dimensional hydrogen-bonded chain composed of water molecules and a squaric acid derivative, H. Terao, T. Sugawara, Y. Kita, N. Sato, E. Kaho and S. Takeda, J. Am. Chem. Soc. 123 (2001) 10468-10474.
· Theoretical study on the topochemical nature in the initiation process of the solid-state thermal isomerization reaction of methyl 4-(dimethyl-amino)benzenesulfonate, M. Oda and N. Sato, J. Phys. Chem. B 102 (1998) 3283-3286.
· A theoretical study on solid-state thermal isomerization reaction of 4-(dimethylamino)benzene-sulfonate in the energetic aspect,M. Oda and N. Sato, Chem. Phys. Lett. 275 (1997) 40-45.
· Crystal structure and solid state reaction of tetrabenzo[de,hi,op,st]-pentacene endoperoxide, A. Izuoka, T. Murase, M. Tukada, Y. Ito, T. Sugawara, A. Uchida, N. Sato and H. Inokuchi, Tetrahedron Lett. 38 (1997) 245-248.
· Change of electronic absorption spectra observed through heating evaporated thin films of a diacetylene compound, N. Sato, M. Oda, T. Okuno, A. Izuoka and T. Sugawara, Mol. Cryst. Liq. Cryst. 277 (1996) 195-203.
· Kinetic feature of nematic phase polymerization of diacetylenes, A. Izuoka, T. Okuno, T. Ito, T. Sugawara, N. Sato, S. Kamei and K. Tohyama, Mol. Cryst. Liq. Cryst. 226 (1993) 201-205.
Molecular aggregates: Electrical property Group
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