Toward Cove-Edged Low Band Gap Graphene Nanoribbons

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.

New advances in nanographene chemistry

“…104,105 Furthermore, ruthenium-or platinum-catalysed electrophilic cycloaromatization of ortho-alkynylated biaryls is a versatile method to form phenanthrene structures, as represented by the conversion of precursor 24 to [6]phenacene 25, which enabled the synthesis of graphene molecule 26 (C52) through subsequent cyclodehydrogenation (Fig. 56,[106][107][108] Here, ICl-mediated cycloaromatization of ortho-alkynylated biaryls can serve as a metal-free alternative method for obtaining halogenated phenacenes, which can be directly used for further coupling reactions or dehalogenated by simple treatment with n-butyllithium. 56,[106][107][108] Here, ICl-mediated cycloaromatization of ortho-alkynylated biaryls can serve as a metal-free alternative method for obtaining halogenated phenacenes, which can be directly used for further coupling reactions or dehalogenated by simple treatment with n-butyllithium.…”

On‐Surface Synthesis of Atomically Precise Graphene Nanoribbons

“…[ 18 ] b) Chevron GNRs, including substitutional doping with zero, [ 15 ] one, [ 23 ] two, [ 23,83 ] and four [ 24 ] nitrogen atoms per precursor molecule. c) Zigzag-like GNRs, including widths N = 5 (with cove defects) [ 84 ] and 6 with and without additional phenyl groups. Figure 2 is complex due to the large number of degrees of freedom involved.…”

Bottom-Up Synthesis of Soluble and Narrow Graphene Nanoribbons Using Alkyne Benzannulations

“…Undesired rearrangements are also possible under Scholl reaction conditions. 30 The bottom-up synthesis of very narrow and atomically precise GNRs has also been accomplished oxidatively on a Au(111) surface 17,[31][32][33][34][35] and also a Cu(111) surface. 36,37 A drawback of surfaceassisted synthesis of GNRs is that this methodology is currently not practical for producing bulk quantities of soluble and processable GNRs.…”