Syntheses and properties of graphyne fragments: Trigonally expanded dehydrobenzo[12]annulenes

Kazukuni Tahara, Yuki Yamamoto, Dustin E. Gross, Hiroyoshi Kozuma, Yoko Arikuma, Koji Ohta, Yoshiko Koizumi, Yuan Gao, Yo Shimizu, Shu Seki, Kenji Kamada, Jeffrey S. Moore, Yoshito Tobe

Research output: Contribution to journalArticlepeer-review

Abstract

We present herein the synthesis and properties of the largest hitherto unknown graphyne fragment, namely trigonally expanded tetrakis(dehydrobenzo[12] annulene)s (tetrakis-DBAs). Intramolecular three-fold alkyne metathesis reactions of hexakis(arylethynyl)DBAs 9 a and 9 b using Fürstner's Mo catalyst furnished tetrakis-DBAs 8 a and 8 b substituted with tert-butyl or branched alkyl ester groups in moderate and fair yields, respectively, demonstrating that the metathesis reaction of this protocol is a powerful tool for the construction of graphyne fragment backbones. For comparison, hexakis(arylethynyl)DBAs 9 c-g have also been prepared. The one-photon absorption spectrum of tetrakis-DBA 8 a bearing tert-butyl groups revealed a remarkable bathochromic shift of the absorption cut-off (λ cutoff) compared with those of previously reported graphyne fragments due to extended π-conjugation. Moreover, in the two-photon absorption spectrum, 8 a showed a large cross-section for a pure hydrocarbon because of the planar para-phenylene-ethynylene conjugation pathways. Hexakis(arylethynyl)- DBAs 9 c-e and 9 g and tetrakis-DBA 8 b bearing electron-withdrawing groups aggregated in chloroform solutions. Comparison between the free energies of 9 e and 8 b bearing the same substituents revealed the more favorable association of the latter due to stronger π-π interactions between the extended π-cores. Polarized optical microscopy observations, DSC, and XRD measurements showed that 8 b and 9 e with branched alkyl ester groups displayed columnar rectangular mesophases. By the time-resolved microwave conductivity method, the columnar rectangular phase of 8 b was shown to exhibit a moderate charge-carrier mobility of 0.12 cm2 V-1 s-1. These results indicate that large graphyne fragments can serve as good organic semiconductors.

Original languageEnglish (US)
Pages (from-to)11251-11260
Number of pages10
JournalChemistry - A European Journal
Volume19
Issue number34
DOIs
StatePublished - Aug 19 2013

Keywords

  • alkynes
  • dehydrobenzoannulenes
  • graphyne
  • metathesis
  • self-assembly

ASJC Scopus subject areas

  • Chemistry(all)

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