Research and Principal Research Interests
(1) Preparation and Properties
of Linear π-Conjugated
Systems with Small HOMO-LUMO Separation
We are involved in
the design, synthesis and study of highly conjugated organic oligomers
and polymers which can be either electrically conducting or electroluminescent.
We are interested in studying how chemical modification of the oligomers,
and polymers affects the bandgap, the electrical conductivity, the transparency
and the light emitting properties of these materials. Further, we are developing
new synthetic methodology for the preparation of these oligomers and polymers.
We are studying cyclopentadithiophenes
with various substituents on the bridging positions to obtain linear p-conjugated
systems with small HOMO-LUMO separation, which, unlike higher bandgap polymers,
will be relatively colorless and transparent in the electrical conducting
state. We have shown that connection of 1,3-dithiole rings on the bridging
position in poly(cyclopentadithiophenes) gave new conducting polymers with
a small bandgap on their neutral state and high conductivity on their doped
state. It is, however, very difficult for a polymer to interpret
a relation between structure and properties due to their polydispersed
nature. So we are also studying oligo(cyclopenta-dithiophenes) as
excellent models for their corresponding polymers as well as novel electronic
and optical materials. We prepared a series of oligo(cyclopentadithiophenes)
such as 1 and then examined using spectroscopic analysis, electrochemical
technique, X-ray structure determination, and quantum calculations. We
showed that the oligomers have an extremely small HOMO-LUMO gap (1.03-1.97
eV). We have also demonstrated that the highly planar structures
of the oligomers and the dimerization of the cyclopentadithiophenes caused
dramatic shift of the HOMO level but not the LUMO level. We are now
attempting the further reduction of HOMO-LUMO gap of the oligomers.
(2) Molecular scale electronics
and nanotechnology - Development of Rapid Building Methods of Novel
Molecular Wire toward a Molecular Computer
progress in the miniaturization of electronic devices will ultimately lead
to the construction of a molecular computer. The components of a molecular
computer will be based on single organic molecules working as switches,
wires and logic gates. Therefore, it is very important to investigate single
molecules in terms of their efficiency and mechanism of intrinsic electrical
conductivity. We are particularly focusing on p-conjugated molecules
as very promising molecular wires, and are studying development of novel
conic molecular wires. Attaching a conjugated molecule to an electrode
through the conic molecular wire is an excellent way to measure the precise
properties of conjugated molecules (Figure). A molecular wire with
a conic shape occupies a large surface area, which limits the number of
molecules in a unit area. It is thus easy to locate and characterize
a single molecular wire. Large contact area also aids the electron
injection into a single molecule without large resistance. The current
research projects include developing effective synthetic metrology for
the preparation of the conic molecular wire with a large base area.
1,"Synthesis and preliminary
testing of molecular wires and devices", J. M. Tour, A. M. Rawlett,
M. Kozaki, Y. X. Yao, R. C. Jagessar, S. M. Dirk, D. W. Price, M. A. Reed,
C. W. Zhou, J. Chen, W. Y. Wang, I. Campbell, Chem.-Eur. J., 7,
neutral and charged species", T. Okamoto, M. Kozaki,
Y. Yamashita, K. Okada, Tetrahedron Lett., 42, 7591-7594
3, "Preparation and Exchange
Interaction of DPPH-Derived Polyradicals", M. Kozaki, S. Nakamura,
T. Okamoto, S. Kanaya, K. Sato, T. Takui, K. Okada, Mol. Cryst. Liq.
Cryst., 334, 131-138 (2001).
4, "Evolution of Strategies
for Self Assembly and Hookup of Molecule-Based Devices", D. L. Allara, T. D. Dunbar,
P. S. Weiss, L. A. Bumm, M. T. Cygan, J. M. Tour, W. A. Reinerth, Y. Yao,
M. Kozaki, L. Jones, II., Anna. N. Y. Acad. Sci. 852,
5, "Preparation and Characterization
of Novel DPPH-based Diradicals", M. Kozaki, S. Nakamura,
K. Sato, T. Takui, T. Kamatani, M. Oda, K. Tokumaru, K. Okada, Tetrahedron
Lett., 39, 5979 (1998).
6, "Exchange Interaction
of Bispyridinyl Diradicals Linked by σ-Frames", K. Matsumoto, M. Oda, M.
Kozaki, K. Sato, T. Takui, K. Okada, Tetrahedron Lett., 39,
7, "A New Photochemical Approach
to Benzylic Polyradicals through C-N Bond Cleavage of a Pyridinyl Radical", H. Mori, M. Kozaki,
K. Sato, T. Takui, K. Okada, Tetrahedron Lett., 39, 6315 (1998).
8, "Molecular Scale Electronics:
A Synthetic/Computational Approach to Digital Computing", J. M. Tour, M. Kozaki,
J. M. Seminario, J. Am. Chem. Soc., 120, 8486-8493 (1998).
9, "New Thiophene-Pyrrole-Derived
Annulenes Containing 6 and 10 Heterocyclic Units", M. Kozaki, J. P.Parakka,
M. P. Cava, J. Org. Chem., 61, 3657 (1996).
10, Preparation and Properties
of Novel Polythiophenes Containing 1,3-Dithiol-2-ylidene Moieties, M. Kozaki, S. Tanaka,
Y. Yamashita, J. Org. Chem., 59, 442 (1994).