title: Synthesis and Characterization of [n]CPP (n = 5, 6, 8, 10, and 12) Radical Cation and Dications: Size-Dependent Absorption, Spin, and Charge Delocalization.
abstract: Radical cations and dications of [n]cyclo-p-phenylenes ([n]CPPs, n = 5, 6, 10, and 12), which are the models of those of linear oligo-p-phenylenes without a terminus, were synthesized as hexafluoroantimonate salts by the one- and two-electron chemical oxidation of CPP by NOSbF6 or SbF5. The radical cations, [n]CPP(•+), and dications, [n]CPP(2+), exhibited remarkable bathochromic shifts in their UV-vis-NIR absorption bands, suggesting that [n]CPP(•+) and larger [n]CPP(2+) exhibit longer polyene character than the shorter analogues. The larger bathochromic shift was consistent with the narrower HOMO-SOMO and HOMO-LUMO gaps in larger [n]CPP(•+) and [n]CPP(2+), respectively. In [n]CPP(•+), the spins and charges were equally and fully delocalized over the p-phenylene rings of the CPPs, as noted by ESR. (1)H NMR revealed that the hydrogen of [n]CPP(2+) shifted to a high magnetic field from the neutral compounds due to the diamagnetic ring current derived from the in-plane aromaticity of [n]CPP(2+). The single resonances observed in all [n]CPP(2+) strongly suggest the complete delocalization of the charges over the CPPs. Furthermore, the contribution of biradical character was clarified for [10]- and [12]CPP by VT-NMR experiment and theoretical calculation.
authors.affiliation: Institute for Chemical Research, Kyoto University , Uji 611-0011, Japan.|Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency , Tokyo 102-0076, Japan.
authors.forename: Eiichi
authors.initials: E
authors.lastname: Kayahara
authors.affiliation: Graduate School of Human and Environmental Sciences, Kyoto University , Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Takahiko
authors.initials: T
authors.lastname: Kouyama
authors.affiliation: Graduate School of Human and Environmental Sciences, Kyoto University , Sakyo-ku, Kyoto 606-8501, Japan.|Institute for Liberal Arts and Sciences, Kyoto University , Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Tatsuhisa
authors.initials: T
authors.lastname: Kato
authors.affiliation: Institute for Chemical Research, Kyoto University , Uji 611-0011, Japan.|Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency , Tokyo 102-0076, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Yamago