Synthetic organic spin chemistry for structurally well-defined open-shell graphene fragments

Abstract

Graphene, a two-dimensional layer of sp2-hybridized carbon atoms, can be viewed as a sheet of benzene rings fused together. Three benzene rings can be combined in three different ways, to yield linear anthracene and angular phenanthrene, where the rings share two C–C bonds, and the phenalenyl structure where three C–C bonds are shared between the rings. This third structure contains an uneven number of carbon atoms and, hence, in its neutral state, an uneven number of electrons — that is, it is a radical. All three structures may be viewed as being sections of graphene. Extension of this concept leads to an entire family of phenalenyl derivatives — 'open-shell graphene fragments' — that are of substantial interest from the standpoint of fundamental science as well as in view of their potential applications in materials chemistry, in particular quantum electronic devices. Here we discuss current trends and challenges in this field.

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Figure 1: Spin density distributions of phenalenyl-based neutral radicals.
Figure 2: Crystal structure and electronic structure of the π-dimer of 3.
Figure 3: Structural change of intra-π-dimer interaction.
Figure 4: ESR spectra, pictures of a rechargeable battery made using a crystalline neutral radical, high-spin magnetic triangulenes, π-extended phenalenyl derivatives, a π-stacked radical polymer, and curved and twisted phenalenyl systems.

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Acknowledgements

We thank Kazuhiro Nakasuji (Fukui University of Technology and Osaka University) for his valuable suggestions and discussions throughout this work. This work was partly supported by Grants-in-Aids for Scientific Research on Innovation Areas (no. 20110006), Elements Science and Technology Project, and Scientific Research on Innovative Areas, 'Quantum Cybernetics', from the Ministry of Education, Culture, Sports, Science and Technology, Japan. Support for the present work by the Japan Science and Technology Agency through the Core Research for Evolutional Science and Technology project 'Implementation of Molecular Spin Quantum Computers' in 'Creation of New Technology Aiming for the Realization of Quantum Information Processing Systems' and the FIRST project 'Quantum Information Processing' Funding Program for World-Leading Innovative R&D on Science and Technology, JSPS, Japan, are also acknowledged.

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Correspondence to Yasushi Morita or Takeji Takui.

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