Cove-Edged Graphene Nanoribbons with Incorporation of Periodic Zigzag-Edge Segments

Abstract

Structurally precision graphene nanoribbons (GNRs) are promising candidates for next-generation nanoelectronics due to their intriguing and tunable electronic structures. GNRs with hybrid edge structures often confer them unique geometries associated with exotic physicochemical properties. Herein, a novel type of cove-edged GNRs with periodic short zigzag-edge segments is demonstrated. The bandgap of this GNR family can be tuned using an interplay between the length of the zigzag segments and the distance of two adjacent cove units along the opposite edges, which can be converted from semiconducting to nearly metallic. A family member with periodic cove-zigzag edges based on N=6 zigzag-edged GNR, namely 6-CZGNR-(2,1), is successfully synthesized in solution through the Scholl reaction of a unique snake-like polymer precursor (10) that is achieved by the Yamamoto coupling of a structurally flexible S-shaped phenanthrene-based monomer (1). The efficiency of cyclodehydrogenation of polymer 10 toward 6-CZGNR-(2,1) is validated by FT-IR, Raman and UV-Vis spectroscopies, as well as by the study of two representative model compounds (2 and 3). Remarkably, the resultant 6-CZGNR-(2,1) exhibits an extended and broad absorption in the nearinfrared region with a record narrow optical bandgap of 0.99 eV among the reported solution-synthesized GNRs. Moreover, 6-CZGNR-(2,1) exhibits a high macroscopic carrier mobility of ~20 cm 2 V -1 s -1 determined by terahertz spectroscopy, primarily due to the intrinsically small effective mass (m*e=m*h=0.17 m0), rendering this GNR a promising candidate for nanoelectronics. ASSOCIATED CONTENT Supporting Information.The Supporting Information is available free of charge at http://pubs.acs.org. Synthetic procedures and characterization data, additional optical, FTIR and Raman spectra of model compounds, STM and AFM characterizations, Solid-state NMR analysis, DFT calculation details, Terahertz spectroscopy, and NMR and mass spectra of new compounds (PDF).

Laser Desorption Ionization of Large Condensed Polycyclic Aromatic Hydrocarbons in Petroleum Pitch and Thermally Treated Products

“…The material mainly consists of polycyclic aromatic hydrocarbons (PAHs) with short alkyl chains. Pitch has a wide range of applications from construction roofing and refractory bricks to electrodes for aluminum and steel manufacture, − and various advanced carbon materials, such as carbon fiber, carbon nanotubes, graphene, carbon composites, etc. In general, petroleum-derived pitch has a lower aromaticity, higher sulfur content, and lower nitrogen content compared to coal tar-derived pitch .…”

Structure-imposed electronic topology in cove-edged graphene nanoribbons

“…With the emergence of precision chemistry, the atomically precise synthesis of graphene nanoribbons (GNRs) with well-defined width, edge structure, and termination has become possible [1][2][3][4]. Besides GNRs with zigzag or armchair edge termination, more complex edges have also been realized [2][3][4][5][6][7][8][9][10][11][12][13]. The edges have determinant impact on the electronic structure of the GNRs.…”

“…The introduction of coves, missing CH groups at the edges, into inherently metallic zigzag GNR provides quantum confinement via a sublattice located at both edges and opens a band gap. ZGNR-C have been realized experimentally [7,13], but up to now their topological states have been predicted only by theory [15]. Although many of the ZGNR-C have been studied to date, there is not yet any rule established that connects their structural topology with their electronic state.…”

“…Unambiguous labelling of cove-edged ZGNR requires three parameters: the width N of the ZGNR, counted as number of zigzag rows of carbon atoms (N ∈ N, N ≥ 3), the distance between coves on the same edge, a, in units of hexagonal rings (a ∈ N, a ≥ 2), which coincides with the repetitive unit cell length, and the shortest offset between adjacent coves on opposite edges of the ribbon, b (b ∈ 0, a 2 ). N -ZGNR-C(a, b) then labels all structurally possible regular ZGNR-C and is equivalent to N -CZGNR-(m,n) introduced by Wang et al with a = m + 1 [7]. This nomenclature is illustrated in Fig.…”

Heteroatom-Doped [4]Triangulene: Facile Synthesis and Two-Dimensional On-Surface Self-Assemblies

“…During the past years, a large number of structurally well-defined NGs with various sizes and topological features have been synthesized in solution and on metal surfaces. [6][7][8][9][10][11][12][13][14][15][16][17] Furthermore, incorporation of heteroatoms has further expanded the possibilities of generating novel structures with desirable properties. [18][19][20][21][22][23] On the other hand, steering molecular assembly to form ordered two-dimensional (2D) networks has attracted much attention due to the superiority of 2D materials for optoelectronic applications.…”