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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Itoh, K. & Kinoshita, M. (eds) Molecular Magnetism 1–347 (Kodansha/Gordon and Breach, 2000).
Miller, J. S. & Drillon, M. (eds) Magnetism: Molecules to Materials II 1–489 (Wiley-VCH, 2001).
Hicks, R. G. What's new in stable radical chemistry? Org. Biomol. Chem. 5, 1321–1338 (2007).
Feringa, B. L. (ed.) Molecular Switches (Wiley-VCH, 2001).
Balzami, V., Credi, A. & Venturi, M. Molecular Devices and Machines 2nd edn (Willey-VCH, 2008).
Coronado, E. & Epstein, A. J. Molecular spintronics and quantum computing. J. Mater. Chem. 19, 1670–1671 (2009).
Sato, K. et al. in Molecular Realizations of Quantum Computing 2007 (eds Nakahara, M. et al.) 58–162 (World Scientific, 2009).
Rahimi, R. et al. Pulsed ENDOR-based quantum information processing. Int. J. Quantum Info. 3, 197–204 (2005).
Morita, Y. & Nishida, S. in Stable Radicals: Fundamental and Applied Aspects of Odd-Electron Compounds (ed. Hicks, R) Ch. 3, (Wiley, 2010).
Sugisaki, K. et al. Spin-orbit contributions in high-spin nitrenes/carbenes: a hybrid CASSCF/MRMP2 study of zero-field splitting tensors. ChemPhysChem 11, 3146–3151 (2010).
Haddon, R. C. Design of organic metals and superconductors. Nature 256, 394–396 (1975).
Novoselov, K. S. et al. Electric field effect in atomically thin carbon films. Science 306, 666–669 (2004).
Geim, A. K. & Novoselov, K. S. The rise of graphene. Nature Mater. 6, 183–191 (2007).
Allen, M. J., Tung, V. C. & Kaner, R. B. Honeycomb carbon: a review of graphene. Chem. Rev. 110, 132–145 (2010).
Clar, E. Polycyclic Hydrocarbon Vol. 1, 24–31 (Academic, 1964).
Inoue, J. et al. The first detection of a Clar's hydrocarbon, 2,6,8-tri-tert-butyltriangulene: a ground-state triplet of non-Kekulé benzenoid hydrocarbon. J. Am. Chem. Soc. 123, 12702–12703 (2001).
Fukui, K. et al. The first non-Kekulé polynuclear aromatic high-spin hydrocarbon: generation of a triangulene derivative and band structure calculation of triangulene-based high-spin hydrocarbons. Synth. Metals 121, 1824–1825 (2001).
Philpott, M. R., Cimpoesu, F. & Kawazoe, Y. Geometry, bonding and magnetism in planar triangulene graphene molecules with D3h symmetry: zigzag C mml_m * * 2 + 4 mml_m + 1 H3 m +3 (m = 2, ..., 15). Chem. Phys. 354, 1–15 (2008).
Goto, K. et al. A stable neutral hydrocarbon radical: synthesis, crystal structure and physical properties of 2,5,8-tri-tert-butyl-phenalenyl. J. Am. Chem. Soc. 121, 1619–1620 (1999).
Morita, Y. et al. A new trend in phenalenyl chemistry: a persistent neutral radical, 2,5,8-tri-tert-butyl-1,3-diazaphenalenyl, and the excited triplet state of the gable syn-dimer in the crystal column motif. Angew. Chem. Int. Ed. 42, 1793–1796 (2002).
Haddon, R. C. et al. 1,9-dithiophenalenyl system. J. Am. Chem. Soc. 100, 7629–7633 (1978).
Beer, L. et al. The first electronically stabilized phenalenyl radical: effect of substituents on solution chemistry and solid-state structure. Cryst. Growth Des. 7, 802–809 (2007).
Beer, L. et al. Tetrathiophenalenyl radical and its disulfide-bridged dimer. Org. Lett. 10, 3121–3123 (2008).
Morita, Y. et al. New persistent radicals: synthesis and electronic spin structure of 2,5-di-tert-butyl-6-oxophenalenoxyl derivatives. J. Am. Chem. Soc. 122, 4825–4826 (2000).
Morita, Y. et al. Topological symmetry control in spin density distribution: spin chemistry of phenalenyl based neutral monoradical systems. Org. Lett. 5, 3289–3291 (2003).
Kaupp, M., Bühl, M. & Malkin, V. G. (eds) Calculation of NMR and EPR Parameters: Theory and Applications (Wiley-VCH, 2004).
Small, D. et al. Intermolecular π-to-π bonding between stacked aromatic dyads. Experimental and theoretical binding energies and near-IR optical transitions for phenalenyl radical/radical versus radical/cation dimerizations. J. Am. Chem. Soc. 126, 13850–13858 (2004).
Suzuki, S. et al. Aromaticity on the pancake-bonded dimer of neutral phenalenyl radical as studied by MS and NMR spectroscopies and NICS analysis. J. Am. Chem. Soc. 128, 2530–2531 (2006).
Mota, F., Miller, J. S. & Novoa, J. J. Comparative analysis of the multicenter, long bond in [TCNE]•– and phenalenyl radical dimers: a unified description of multicenter long bonds. J. Am. Chem. Soc. 131, 7699–7707 (2009).
Chi, X. et al. Dimeric phenalenyl-based neutral radical molecular conductors. J. Am. Chem. Soc. 123, 4041–4048 (2001).
Itkis, M. E., Chi, X., Cordes, A. W. & Haddon, R. C. Magneto-opto-electronic bistability in a phenalenyl-based neutral radical. Science 296, 1443–1445 (2002).
Pal, S. K. et al. Resonating valence-bond ground state in a phenalenyl-based neutral radical conductor. Science 309, 281–284 (2005).
Shimizu, A. et al. Resonance balance shift in stacks of delocalized singlet biradicals. Angew. Chem. Int. Ed. 48, 5482–5486 (2009).
Morita, Y. et al. Thermochromism in an organic crystal based on the coexistence of σ- and π-dimers. Nature Mater. 7, 48–51 (2008).
Nishida, S. et al. Spin transfer and solvato-/thermochromism induced by intramolecular electron transfer in a purely organic open-shell system. Angew. Chem. Int. Ed. 44, 7277–7280 (2005).
Morita, Y. et al. Redox-based spin diversity in a 6-oxophenalenoxyl system: generation, ESR/ENDOR/TRIPLE, and theoretical studies of 2,5,8-tri-tert-butylphenalenyl-1,6-bis(olate) salts. Org. Lett. 4, 1985–1988 (2002).
Morita, Y., Nishida, S., Kawai, J., Takui, T. & Nakasuji, K. Oxophenalenoxyl: novel stable neutral radicals with a unique spin-delocalized nature depending on topological symmetries and redox state. Pure Appl. Chem. 47, 507–517 (2008).
Morita, Y., Okafuji, T. & Satoh, M. Molecular crystalline rechargeable battery. Japanese patent JP2007227186 A 20070906 (2007).
Enoki, T., Kobayashi, Y. & Fukui, K. Electronic structures of graphene and nanographene. Int. Rev. Phys. Chem. 26, 609–645 (2007).
Shohoji, M. C. B. L. et al. Electronic quartet and triplet states of polyanionic C60 fullerene and their anomalous spin relaxation as studied by cw-ESR/2D-electron spin transient nutation spectroscopy. J. Am. Chem. Soc. 122, 2962–2963 (2000).
Rath, H. et al. A stable organic radical delocalized on a highly twisted π system formed upon palladium metalation of a Möbius aromatic hexaphyrin. Angew. Chem. Int. Ed. 49, 1489–1491 (2010).
Morita, Y. et al. Curved aromaticity of a corannulene-based neutral radical: crystal structure and 3D unbalanced-delocalization of spin. Angew. Chem. Int. Ed. 47, 2035–2038 (2008).
Ueda, A. et al. Three-dimensional intramolecular exchange interaction in a curved and nonalternant π-conjugated system: corannulene with two phenoxyl radicals. Angew. Chem. Int. Ed. 49, 1678–1682 (2010).
Zak, J. K., Miyasaka, M., Rajca, S., Lapkowski, M. & Rajca, A. Radical cation of helical, cross-conjugated β-oligothiophene. J. Am. Chem. Soc. 132, 3246–3247 (2010).
Nishida, S. et al. Curve-structured phenalenyl chemistry: synthesis, electronic structure, and bowl-inversion barrier of a phenalenyl-fused corannulene anion. J. Am. Chem. Soc. 130, 14954–14955 (2008).
Sato, K. et al. Implementation of molecular spin quantum computing by pulsed ENDOR technique: direct observation of quantum entanglement and spinor. Physica E 40, 363–366 (2007).
Sato, K. et al. Molecular electron-spin quantum computers and quantum information processing: pulse-based electron magnetic resonance spin technology applied to matter spin-qubits. J. Mater. Chem. 19, 3739–3754 (2009).
Morita, Y. et al. Triple-stranded metallo-helicates addressable as Lloyd's electron spin qubits. J. Am. Chem. Soc. 132, 6944–6946 (2010).
Lanyon, B. P. et al. Towards quantum chemistry on a quantum computer. Nature Chem. 2, 106–111 (2010).
Webb, G. A. (ed.) Modern Magnetic Resonance 643–650 (Springer, 2007).
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.
The authors declare no competing financial interests.
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