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Synthesis and Structure–Property Relationships of 2,2′-Bis(benzo[b]phosphole) and 2,2′-Benzo[b]phosphole–Benzo[b]heterole Hybrid π Systems

Authors

  • Yukiko Hayashi,

    1. Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan), Fax: (+81) 75-383-2571
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  • Prof. Dr. Yoshihiro Matano,

    Corresponding author
    1. Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan), Fax: (+81) 75-383-2571
    • Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan), Fax: (+81) 75-383-2571
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  • Kayo Suda,

    1. Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan)
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  • Prof. Dr. Yoshifumi Kimura,

    1. Department of Chemical Science and Technology, Faculty of Bioscience and Applied Chemistry, Hosei University, Tokyo 184-8584 (Japan)
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  • Prof. Dr. Yoshihide Nakao,

    1. Fukui Institute for Fundamental Chemistry, Kyoto University, Sakyo-ku, Kyoto 606-8103 (Japan)
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  • Prof. Dr. Hiroshi Imahori

    1. Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan), Fax: (+81) 75-383-2571
    2. Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan)
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Abstract

The first comprehensive study of the synthesis and structure–property relationships of 2,2′-bis(benzo[b]phosphole)s and 2,2′-benzo[b]phosphole–benzo[b]heterole hybrid π systems is reported. 2-Bromobenzo[b]phosphole P-oxide underwent copper-assisted homocoupling (Ullmann coupling) and palladium-catalyzed cross-coupling (Stille coupling) to give new classes of benzo[b]phosphole derivatives. The benzo[b]phosphole–benzo[b]thiophene and -indole derivatives were further converted to P,X-bridged terphenylenes (X=S, N) by a palladium-catalyzed oxidative cycloaddition reaction with 4-octyne through the Cβ[BOND]H activation. X-ray analyses of three compounds showed that the benzo[b]phosphole-benzo[b]heterole derivatives have coplanar π planes as a result of the effective conjugation through inter-ring C[BOND]C bonds. The π–π* transition energies and redox potentials of the cis and trans isomers of bis(benzo[b]phosphole) P-oxide are very close to each other, suggesting that their optical and electrochemical properties are little affected by the relative stereochemistry at the two phosphorus atoms. The optical properties of the benzo[b]phosphole–benzo[b]heterole hybrids are highly dependent on the benzo[b]heterole subunits. Steady-state UV/Vis absorption/fluorescence spectroscopy, fluorescence lifetime measurements, and theoretical calculations of the non-fused and acetylene-fused benzo[b]phosphole–benzo[b]heterole π systems revealed that their emissive excited states consist of two different conformers in rapid equilibrium.

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