| Co-Investigator(Kenkyū-buntansha) |
NIIMOTO Yoshihide Sumika Fine Chemicals Ltd., Group manager (Researcher), グループマネージャー
MASAKI Yasuhiro University of Tokyo, College of Art and Science, Research Associate, 教養学部, 助手 (60199677)
YAMAMOTO Koji University of Osaka Prefecture, Faculty of Integrated Arts and Sciences, Profess, 総合科学部, 教授 (80029438)
YANO Shigenobu Nara Women's University, Faculty of Science, Professor, 理学部, 教授 (60011186)
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| Research Abstract |
To date, conjugated systems, each being composed of a donor, an aromatic ring and an acceptor, have been the well-known non-linear optical materials, in particular, for the purpose of second harmonic generation. We consider that the main role of the aromatic ring are to decrease donation of pi-electron from the donor to the acceptor in the electronically ground state and, accordingly, to relatively enhance the interaction in the electronically excited state. In spite of the marked efficiency of these systems, the recent examinations have stressed that the closed-shell character of the aromatic rings endows the systems with the upper-limit as non-linear optical materials.
A trivalent boron is isoelectronic to a carbocation. Hence, it behaves as a pi-electron acceptor. Due to the electropositivity, however, its pi-type conjugation with the carbon atom is considered to be weak like the closed-shell aromatic rings. From this viewpoint we examined borepin annelated with heteroles, such as th
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e pyrrole or thiophene rings both of which are electron donors. After some trials, synthesis of 1-phenylthieno- [3,4-d] borepin (1), 1-phenylthieno [2,3-d] borepin (2), 5-Methyl-1-phenylpyrrolo [3,4-d] borepin (3), and 5-tris (isopropylsilyl)-1-phenylpyrrolo [3,4-d] borepin (4) were achieved. The methods developed are generally useful for the synthesis of conjugated aromatics involving a boron atom. The marked difference in reactivity toward acetic acid was observed with the change of the annelation modes of borepin and heterole rings. The shifts of fluorescent emissions showed the clear linear relationship with the change of solvent-polarity and indicated that the dipole moment of each compound in the excited state is much larger than that in the ground state. The moderate blue-light transparency was observed, despite the above-mentioned charge-transfer character in the excited state.
These findings indicate that conjugated systems involving the boron atom are useful as non-linear optical materials. Less
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