Organic Materials Chemistry

Masatoshi Kozaki (Professor)

1. Current 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 
   Extremely rapid 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.

2. Selected Publications

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, 5118-5134 (2001).

2, "Benzoxazinophenoxazines: neutral and charged species", T. Okamoto, M. Kozaki, Y. Yamashita, K. Okada, Tetrahedron Lett., 42, 7591-7594 (2001).

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, 349-370 (1998)

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, 6307 (1998). 

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).