Toward cove-edged low band gap graphene nanoribbons

Junzhi Liu; Bo-Wei Li; Yuan-Zhi Tan; Angelos Giannakopoulos; Carlos Sanchez-Sanchez; David Beljonne; Pascal Ruffieux; Roman Fasel; Xinliang Feng; Klaus Müllen

doi:10.1021/jacs.5b03017

Toward cove-edged low band gap graphene nanoribbons

J Am Chem Soc. 2015 May 13;137(18):6097-103. doi: 10.1021/jacs.5b03017. Epub 2015 May 4.

Authors

Affiliations

¹ †Max-Planck Institut für Polymerforschung, Ackermannweg 10, 55128, Mainz, Germany.
² ‡State Key Laboratory of Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, China.
³ §Laboratory for Chemistry of Novel Materials, University of Mons, Place du Parc 20, B-7000 Mons, Belgium.
⁴ ∥Nanotech@surfaces Laboratory, Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland.
⁵ ⊥Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland.

Abstract

Graphene nanoribbons (GNRs), defined as nanometer-wide strips of graphene, have attracted increasing attention as promising candidates for next-generation semiconductors. Here, we demonstrate a bottom-up strategy toward novel low band gap GNRs (Eg = 1.70 eV) with a well-defined cove-type periphery both in solution and on a solid substrate surface with chrysene as the key monomer. Corresponding cyclized chrysene-based oligomers consisting of the dimer and tetramer are obtained via an Ullmann coupling followed by oxidative intramolecular cyclodehydrogenation in solution, and much higher GNR homologues via on-surface synthesis. These oligomers adopt nonplanar structures due to the steric repulsion between the two C-H bonds at the inner cove position. Characterizations by single crystal X-ray analysis, UV-vis absorption spectroscopy, NMR spectroscopy, and scanning tunneling microscopy (STM) are described. The interpretation is assisted by density functional theory (DFT) calculations.