Bulk properties of solution-synthesized chevron-like graphene nanoribbons

Abstract

Graphene nanoribbons (GNRs) have received a great deal of attention due to their promise for electronic and optoelectronic applications. Several recent studies have focused on the synthesis of GNRs by the bottom-up approaches that could yield very narrow GNRs with atomically precise edges. One type of GNRs that has received a considerable attention is the chevron-like GNR with a very distinct periodic structure. Surface-assisted and solution-based synthetic approaches for the chevron-like GNRs have been developed, but their electronic properties have not been reported yet. In this work, we synthesized chevron-like GNRs in bulk by a solution-based method, characterized them by a number of spectroscopic techniques and measured their bulk conductivity. We demonstrate that solution-synthesized chevron-like GNRs are electrically conductive in bulk, which makes them a potentially promising material for applications in organic electronics and photovoltaics.

New advances in nanographene chemistry

“…However, the AA-type Yamamoto polymerization of monomer 118 afforded polyphenylene precursor 119 with a relatively low M w of 10 000 g mol À1 , an M n of 7200 g mol À1 and a PDI of 1.4 based on SEC analysis against a PS standard, presumably because of high steric hindrance during the polymerization. 243 Moreover, using the same synthetic strategy, Sinitskii et al conducted a solution synthesis of N-doped, chevron-type GNR 126, starting from 5-(6,11-dibromo-1,3,4-triphenyltriphenylen-2-yl)pyrimidine (124) (Fig. These results indicated that the obtained GNR 120 was rather short, and mixed with oblong-shaped graphene molecules, based on the definition given in the introduction.…”

Aggregation of atomically precise graphene nanoribbons

“…2,45 Our prior studies on the solutionsynthesized GNRs also include the results of their bulk characterization by spectroscopic techniques, such as XPS, EDX, NMR, UV-vis-NIR, FTIR and Raman spectroscopy. 2,5,44 Unlike other solution-synthesized GNRs that have been recently reported, 3,4,7,[9][10][11]13,49 these chevron GNRs do not contain any alkyl groups to increase their solubility. In this paper we will not discuss in detail the advantages (mostly the increased solubility) and disadvantages (such as, for example, inferior electrical contacts between nanoribbons in bulk GNR materials and composites) of such alkyl-substituted GNRs.…”

“…38,56 Importantly, UV-vis-NIR absorption spectroscopy is oen used to probe optoelectronic properties of synthetic GNRs and in particular, to measure their optical band gaps. [2][3][4][5][7][8][9]49 While it is generally recognized that the optically measured band gaps of GNRs are smaller than their intrinsic band gaps because of the excitonic effects, 54 understanding bulk properties of GNRs is important for various large-scale applications of nanoribbons within thin lms, coatings and composites. The results presented in this study show that (1) the spectroscopic features observed in the experimentally measured absorbance spectra of chevron GNRs are in a good agreement with theoretically predicted excitionic transitions, 39 and (2) the appearance of an absorbance spectrum could depend on the aggregation state of GNRs, which would affect the position of the absorbance edge and hence the measured optical band gap.…”

“…Because of recent advances in bottom-up solution synthesis of GNRs, nanoribbons with narrow widths (w < 2 nm) and atomically precise edges can now be produced in large quantities. [2][3][4][5][6][7][8][9][10][11][12][13][14] However, handling and processing of nanoribbons for the fabrication of macroscopic structures, such as bers or lms, could be challenging because of the GNRs' tendency for entanglement, aggregation, and thus poor solubility in conventional solvents. This problem appears to be general for one-dimensional (1D) nanomaterials, such as metallic and semiconductor nanowires and carbon nanotubes (CNTs), whose precise nanoscale assembly and alignment present a formidable challenge.…”

“…These nanoribbons already have been a subject of several theoretical [39][40][41] and experimental studies. 2,5,[42][43][44][45][46][47][48] We investigated chevron GNRs in solution and found that their optical properties depend on their aggregation state. We also found that in addition to forming bulk aggregates of the p-p stacked nanoribbons, on surfaces GNRs can assemble to form long one-dimensional (1D) structures.…”