Graphene Nanoribbons by Chemists: Nanometer‐Sized, Soluble, and Defect‐Free

Abstract

Closing the zipper: A method for the bottom‐up organic synthesis of defect‐free graphene nanoribbons in solution has been developed. Polyphenylene precursors with a unique kinked backbone enabled full cyclodehydrogenation in a single reaction step by an intramolecular Scholl reaction with FeCl3 (see scheme).

Bulk properties of solution-synthesized chevron-like graphene nanoribbons

“…Several recent studies have focused on the synthesis of GNRs by the bottom-up approaches that rely on building GNRs from smaller molecular species. [7][8][9][10][11][12][13][14][15][16][17][18][19][20] The resulting GNRs are very narrow (typically with widths, w < 2 nm) and have atomically precise edges, which is very important for potential applications. [3][4][5][6]21,22 One type of synthetic GNRs that has received considerable theoretical [23][24][25] and experimental attention 9,16,19,20,26 is the chevron-like GNR that has a very distinct periodic structure (Fig.…”

Chemical synthesis of graphene nanoribbons

“…On this basis, producing GNRs with tailor-made predefined widths, edge structure geometries and suitable solubility constitutes an important challenge for synthetic chemists. Bottom-up approaches reported to date include organic synthesis in solution via crosscoupling of the appropriate organic building-blocks followed by the dehydrogenation of the resulting oligomers, 37,38,[40][41][42][43][44][45][46][47] the conversion of precursors inside CNTs, 48,49 and surface-assisted polymerization with subsequent dehydrogenation in an ultra-high vacuum environment. 39,50,51 Although these bottom-up methods provide GNRs with a defined edge structure, they so far suffer from the inability to afford GNRs having variable widths at large scales, owing to the low solubility of the synthesized GNRs, and/or the need for highly-specialized instrumentation.…”

“…41 Related work by Müllen and collaborators 42 used microwave assisted Diels-Alder reactions to obtain five monodisperse ribbon-type polyphenylenes with rigid dibenzo[e,l]pyrene cores in their repeat units. These polyphenylenes served as precursors for giant PAH ribbons and were variable in terms of the carbon atoms present in the aromatic backbone, ranging from 132 to 372 carbon atoms and, moreover, incorporated up to six dibenzo[e,l]pyrene units, thus showing quite different aspect ratios (Scheme 4, GNR4).…”

“…42 Two years later, the same research group reported the synthesis of a series of nanoribbons derived from polyphenylene precursors with a non rigid kinked backbone (Scheme 6, GNR5a-c type) 43 that showed higher solubility compared to the previously reported rigid linear poly(paraphenylene) systems. 42,52 For the preparation of the precursor polymers, microwave assisted Suzuki-Miyaura coupling polymerization was used. The absence of backbone rigidity facilitated the synthesis of high molecular weight polymers (up to 16.000 g mol -1 ).…”

“…Then, a Diels-Alder cycloaddition with a functionalized tetraphenylcyclopentadienone monomer under microwave conditions efficiently produced the paraterphenyl-based oligophenylene precursor in 85% yield. 42 that the same group had previously used for the preparation of GNRs precursors. The final synthetic step, Scholl cyclodehydrogenation of the two polymer precursors using FeCl 3 as oxidant in a mixture of dichloromethane and nitromethane, afforded the two target GNRs (Scheme 7, GNR6a-b).…”