1. Discovery and Verification of Electric Conduction in Conjugated π-Electron Molecular Solids．
(see Chapters I, II and V in the list of publications)

Through physicochemical studies on carbon and graphite, Prof. Hiroo Inokuchi initiated measurements of electrical conductivity in condensed polycyclic aromatic (π-electron) compounds such as violanthrone, isoviolanthrone and pyranthrone,(1) and verified in the most convincing way that intermolecular electron transfer is mediated by intermolecular overlap of the π-electrons. Electrical conductivity was found to clearly increase with the application of high pressure,(2) and to decrease when the π-electrons were removed through hydrogenation.(3) He named these polycyclic π- electron compounds 'organic semiconductors' since their conductivities increase with temperature.(1)

Prof. Inokuchi extended his π-electron materials to include charge-transfer complexes, and discovered extraordinarily high conductivities in a perylene-bromine complex.(4) This was the seminal breakthrough from organic semiconductors to organic conductors, which finally led to organic superconductors. Along this research line, the first successful organic metal was TTF-TCNQ studied by Heeger et al., but due to the one-dimensional（1D）nature of this compound, the metal-insulator (M-I) transition at low temperatures presented a crucial obstacle to realizing a superconducting state. Prof. Inokuchi tackled and overcame this difficulty with an ingenious molecular design to elevate the dimensionality of these materials to 2-D and suppress the M-I transition. He measured and confirmed a persistent metallic nature in (BEDT-TTF)₂ClO₄ for the first time,(5) and finally succeeded in creating superconductors(6) based on BEDT-TTF salts, which now comprise the largest family of organic superconductors.

Prof. Inokuchi also was influential in the area of single component molecular materials. He proposed the idea of the 'molecular fastener effect', which involves the enhancement of intermolecular interactions due to the additivity of van der Waals interactions between long-chain hydrocarbons. This idea was successfully realized in a variety of compounds.(7,8)

Eventually, Prof. Inokuchi developed the concept of 'molecular electronics' through his studies of organic materials with π-electron functionality.(9,10) He identified three important functions in molecular devices: the transport, storage, and regulation of electrons in molecular materials. Over the past 40 years, his studies on the electron transport properties of molecular conductors have set the standard for the field that he largely created. The field of organic electro-conductive polymers and their applications also originated from Prof. Inokuchi’s work. In addition, he investigated graphite intercalation compounds for the storage of electrons and several photochromic compounds as regulators of electron flow．As demonstrated above, Prof. Inokuchi was the pioneer and still is the leader in the field of molecular electronics.

2. Catalytic Activity of Organic Materials.
(see Chapters II, IV in the list of publications)

Prof. Inokuchi exploited π-electron functionality to design molecular catalysts. He was the first to observe that the ortho-para hydrogen conversion reaction proceeded very rapidly in polycyclic aromatic hydrocarbon-alkali metal charge transfer complexes, and reached the conclusion that the catalytic activity was mediated by the degree of charge-transfer interaction.(11)　In fact，this important discovery sparked an explosion of studies on catalysis by charge transfer complexes (electron donor-accepter catalysts). He intensively investigated charge transfer complexes such as tetracyanopyrene-cesium complexes,(11) graphite intercalation compounds,(12) chloranil-alkali metal complexes, and cytochrome c₃.(13) These studies established that the reactivity was closely related to the electric and magnetic properties of the molecular catalysts; once again the charge transfer played a vital role.(14) In particular, Prof. Inokuchi observed a high metallic conductivity of a cytochrome c3 thin film under hydrogen over a specific temperature range.(15) As demonstrated above, Prof. Inokuchi has made an important contribution to the creation of the new field of molecular catalysis.

3. Ultraviolet (U. V.) Photoelectron Spectroscopy for Organic Solids．
(see Chapter III in the list of publications)

Beginning in 1963，Prof. Inokuchi developed U. V. photoelectron spectroscopy to investigate the electronic structures of organic thin films.(16) By analyzing the kinetic energy of photoelectrons emitted from the films, he provided key information on the electronic structure of more than 100 organic compounds.(17,18) Information such as the ionization potentials, polarization energies, and band gap energies of the compounds provides a very useful and powerful guide for the characterization of typical organic solids（including polymers）, as well as enabling a systematic search for functional molecular materials such as those used in organic electro-luminescent displays and photovoltaic cells.(19) The recent development of molecular electronics owes much to Prof. Inokuchi's pioneering work on the fundamentals of photoelectron spectroscopy.

References

1. (1)H. Akamatu and H. Inokuchi, J. Chem. Phys., 18, 810 (1950).
2. (2)H. Inokuchi, Bull. Chem. Soc. Jpn., 28, 570 (1955).
3. (3)H. Inokuchi, Bull. Chem. Soc. Jpn., 24, 222 (1951).
4. (4)H. Akamatu, H. Inokuchi and Y. Matsunaga, Nature, 173, 168 (1954).
5. (5)G. Saito, T. Enoki, K. Toriumi, and H. Inokuchi, Solid State Commun. 42, 557 (1982).
6. (6)T. Mori and H. Inokuchi, Solid State Commun., 64, 335 (1987).
7. (7)H. Inokuchi, G. Saito, P.J.Wu, K. Seki, T. B. Tang, T. Mori, K. Imaeda, T. Enoki, Y. Higuchi, K. Inaka and N. Yasuoka, Chem. Lett., 1263　(1986).
8. (8)K. Seki, T. B. Tang, T. Mori, P.J.Wu, , G. Saito, and H. Inokuchi, J. Chem. Soc. Faraday Trans. 2, 82 1067 (1986).
9. (9)H. Inokuchi, Int. Rev. Phys. Chem. 8, 95 (1989).
10. (10)H. Inokuchi, Organic Electronics 7, 62 (2006).
11. (11)T. Kondow, H. Inokuchi and N. Wakayama, J. Chem. Phys., 43, 3766 (1965).
12. (12)T. Enoki, S. Miyajima, M. Sano, and H. Inokuchi, J. Mater. Res. 5, 435 (1990).
13. (13)T. Yagi, M. Tsuda, Y. Mori and H. Inokuchi, J. Am. Chem. Soc.，91, 2801 (1969).
14. (14)H. Inokuchi，Discussion Faraday Soc., 51, 183 (1971).
15. (15)K. Kimura, Y. Nakahara, T. Yagi and H. Inokuchi, J. Chem. Phys.，70, 3317 (1979).
16. (16)H. Inokuchi and Y. Harada, Nature, 198, 477 (1963).
17. (17)M. Kochi, Y. Harada, T. Hirooka, and H. Inokuchi, Bull. Chem. Soc. Jpn., 43, 2690 (1970).
18. (18)N. Sato, K. Seki, and H. Inokuchi, J. Chem. Soc. Faraday Trans. 2, 77 1621 (1981).
19. (19)H. Inokuchi，K. Seki, and N. Sato，Physica Scripta，T17，93 (1987).