Kinetically blocked stable heptazethrene and octazethrene: Closed-shell or open-shell in the ground state?

Yuan Li, Wee Kuan Heng, Byung Sun Lee, Naoki Aratani, José L. Zafra, Nina Bao, Richmond Lee, Young Mo Sung, Zhe Sun, Kuo Wei Huang, Richard D. Webster, Juan T. López Navarrete, Dongho Kim, Atsuhiro Osuka, Juan Casado, Jun Ding, Jishan Wu

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231 Citations (Scopus)


Polycyclic aromatic hydrocarbons with an open-shell singlet biradical ground state are of fundamental interest and have potential applications in materials science. However, the inherent high reactivity makes their synthesis and characterization very challenging. In this work, a convenient synthetic route was developed to synthesize two kinetically blocked heptazethrene (HZ-TIPS) and octazethrene (OZ-TIPS) compounds with good stability. Their ground-state electronic structures were systematically investigated by a combination of different experimental methods, including steady-state and transient absorption spectroscopy, variable temperature NMR, electron spin resonance (ESR), superconducting quantum interfering device (SQUID), FT Raman, and X-ray crystallographic analysis, assisted by unrestricted symmetry-broken density functional theory (DFT) calculations. All these demonstrated that the heptazethrene derivative HZ-TIPS has a closed-shell ground state while its octazethrene analogue OZ-TIPS with a smaller energy gap exists as an open-shell singlet biradical with a large measured biradical character (y = 0.56). Large two-photon absorption (TPA) cross sections (σ(2)) were determined for HZ-TIPS (σ(2)max = 920 GM at 1250 nm) and OZ-TIPS (σ(2)max = 1200 GM at 1250 nm). In addition, HZ-TIPS and OZ-TIPS show a closely stacked 1D polymer chain in single crystals.

Original languageEnglish
Pages (from-to)14913-14922
Number of pages10
JournalJournal of the American Chemical Society
Issue number36
Publication statusPublished - 2012 Sept 12

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry


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