Synthesis of structurally well-defined and liquid-phase-processable graphene nanoribbons

Journal name:
Nature Chemistry
Volume:
6,
Pages:
126–132
Year published:
DOI:
doi:10.1038/nchem.1819
Received
Accepted
Published online

Abstract

The properties of graphene nanoribbons (GNRs) make them good candidates for next-generation electronic materials. Whereas ‘top-down’ methods, such as the lithographical patterning of graphene and the unzipping of carbon nanotubes, give mixtures of different GNRs, structurally well-defined GNRs can be made using a ‘bottom-up’ organic synthesis approach through solution-mediated or surface-assisted cyclodehydrogenation reactions. Specifically, non-planar polyphenylene precursors were first ‘built up’ from small molecules, and then ‘graphitized’ and ‘planarized’ to yield GNRs. However, fabrication of processable and longitudinally well-extended GNRs has remained a major challenge. Here we report a bottom-up solution synthesis of long (>200 nm) liquid-phase-processable GNRs with a well-defined structure and a large optical bandgap of 1.88 eV. Self-assembled monolayers of GNRs can be observed by scanning probe microscopy, and non-contact time-resolved terahertz conductivity measurements reveal excellent charge-carrier mobility within individual GNRs. Such structurally well-defined GNRs may prove useful for fundamental studies of graphene nanostructures, as well as the development of GNR-based nanoelectronics.

At a glance

Figures

  1. Structures of compounds and light-scattering characterization of precursor 2.
    Figure 1: Structures of compounds and light-scattering characterization of precursor 2.

    a, Schematic synthetic route to longitudinally extended GNR 3 via AB-type Diels–Alder polymerization of monomer 1. Precursor 2 was graphitized into GNR 3 by intramolecular oxidative cyclodehydrogenation. b, Translation diffusion, D0, of precursor 2 as a function of the flexibility ratio L/lK for two different contour lengths L (green line, 480 nm; blue line, 110 nm) and Kuhn segment length, lK. The vertical lines correspond to the values of L/lK obtained from Supplementary equation (13). Inset: normalized static light-scattering intensity (Rvv(cm−1) is the absolute Rayleigh ratio, K(mol g−2 cm2) is the optical constant and c(g cm−3) is the solute concentration, and the size of the symbols captures the experimental error) at different wave vectors represented by Supplementary equation (11) yields the molecular weight Mw and the radius of gyration Rg of precursor 2. In addition, access to the translation diffusion D0 (main plot) reveals an unexpectedly large lK of 18 nm (about 25 repeat units) for precursor 2. c, Structure of dimer 4. d, Structure of trimer 5. Structures of GNR 3, dimer 4 and trimer 5 were optimized by Merck Molecular Force Field 94 (MMFF94) calculations. Grey, carbon; white, hydrogen, r.t., room temperature.

  2. Spectroscopic characterization of GNR 3.
    Figure 2: Spectroscopic characterization of GNR 3.

    a, Representative FTIR spectral regions of polyphenylene precursor 2 (red lines) and GNR 3-I (blue lines) show disappearance of the bands derived from mono- and disubstituted benzene rings on graphitization. b, Raman spectrum of GNR 3-I measured at 532 nm (2.33 eV) on a powder sample with laser power below 0.1 mW. The inset shows a magnified area of the spectrum (black oblong, bottom left) to display a peak from the RBLM at 235 cm−1. Observation of the width-specific RBLM corroborates the high uniformity of the GNRs. c, Normalized UV-vis absorption spectra of GNR 3-I (in NMP, blue line) in comparison with those of dimer 4 (in THF, yellow line) and trimer 5 (in THF, red line). The optical bandgaps of dimer 4, trimer 5 and GNR 3 are 1.88, 2.24 and 2.09 eV, respectively, based on the absorption edges, which demonstrates the lowering of the bandgap upon the longitudinal extension. Inset: photographs show dispersions of 3, 4 and 5. a.u., arbitrary units.

  3. STM and AFM characterization of GNRs 3-I and 6.
    Figure 3: STM and AFM characterization of GNRs 3-I and 6.

    a, STM image of GNR 3-I on HOPG (dry film) demonstrates a well-organized self-assembled monolayer of straight and uniform nanoribbons of up to about 60 nm in length. b, Height profile (Z) along the blue line in a; (X) shows the periodicity of the structures formed by GNR 3-I on a HOPG surface, which indicates partial stacking of the GNRs. c, Molecular model of partially stacked GNR 3-I. d, AFM phase image of GNR 6 on HOPG (dry film) demonstrates a highly organized self-assembled monolayer of straight and uniform nanoribbons of over 200 nm in length. e, Molecular structure of GNR 6. f, Profile (along the blue line in d) of the AFM phase image of GNR 6 displays a periodicity in agreement with the expected width of the GNRs, including the alkyl chains. g, Molecular model of GNR 6. Blue, carbon; grey, hydrogen.

  4. Ultrafast photoconductivity of GNR 3-II.
    Figure 4: Ultrafast photoconductivity of GNR 3-II.

    a, Real and imaginary components of the complex photoinduced conductivity of GNRs dispersed in TCB as a function of time after excitation. Excitation wavelength was 400 nm. A quick rise in both real and imaginary conductivity is observed after excitation at time 0, followed by a slower decay. Real conductivity is an indication of photoexcited free-charge carriers present just after excitation. Thick solid lines represent simulations that reveal free-carrier lifetimes of ~1 ps. b, Frequency-resolved complex photoconductivity of the GNR dispersion scaled to an initial surface excitation density N. The frequency-resolved conductivity was measured 300 fs after excitation, at the peak of the photoconductivity, at an absorbed fluence of 4.3 × 1018 photons m−2. Solid lines through the data points are guides to the eye. Error bars on the conductivity in b show plus/minus the standard deviation obtained from 15 consecutive measurements of the THz waveform. Systematic errors, for instance in the independent determination of N, can also affect the magnitude (not the shape) of the scaled conductivity. We estimate the possible magnitude of the systematic errors to be about 25%. Peak magnitudes in a are scaled to the frequency averaged conductivities of b.

Compounds

5 compounds View all compounds
  1. 2,5-Bis(4-dodecylphenyl)-3-(3-ethynylphenyl)-4-phenyl-2,4-cyclopentadienone
    Compound 1 2,5-Bis(4-dodecylphenyl)-3-(3-ethynylphenyl)-4-phenyl-2,4-cyclopentadienone
  2. Tetrabenzo[jk,mn,pq,st]dibenzo[3,4:9,10]phenanthro[1',10',9',8':5,6,7,8]perylo[2,1,12,11-bcdef]ovalene,2,5,8,11,15,18,21,24-octakis(n-dodecyl)
    Compound 4 Tetrabenzo[jk,mn,pq,st]dibenzo[3,4:9,10]phenanthro[1',10',9',8':5,6,7,8]perylo[2,1,12,11-bcdef]ovalene,2,5,8,11,15,18,21,24-octakis(n-dodecyl)
  3. 6,11,20,25,45,57,62,71,76,96-Decadodecylpentatriacontacyclo[28.0.72.02,15.016,29.09,14.013,18.017,22.03,8.031,36.04,32.037,102.023,28.027,101.038,99.039,92.035,40.093,98.041,90.086,91.042,47.034,43.048,89.082,87.051,88.085,94.078,83.052,81.050,55.053,66.054,59.067,80.074,79.068,73.064,69.060,65]102nea-1,3(8),4,6,9,11,13,15,17(22),18,20,23,25,27,29,31,33,35,37(102),38(99),39,41(90),42,44,46,48(89),49,51(88),52(81),53(66),54,56,58,60(65),61,63,67(80),68,70,72,74(79),75,77,82,84,86,91,93,95,97,100-henpentacontaene
    Compound 5 6,11,20,25,45,57,62,71,76,96
    -Decadodecylpentatriacontacyclo[28.0.72.02,15.016,29.09,14.013,18.017,22.03,8.031,36.04,32.037,102.023,28.027,101.038,99.
    039,92.035,40.093,98.041,90.086,91.042,47.034,43.048,89.082,87.051,88.085,94.078,83.052,81.050,55.053,66.054,59.067,80.
    074,79.068,73.064,69.060,65]102nea-1,3(8),4,6,9,11,13,15,17(22),18,20,23,25,27,29,31,33,35,37(102),38(99),39,41(90),42,44,46,48(89),49,51(88),52(81),
    53(66),54,56,58,60(65),61,63,67(80),68,70,72,74(79),75,77,82,84,86,91,93,95,97,100-henpentacontaene
  4. 4-Dodecyl-4',5',6',3''',4''',5''',6'''-heptakis(4-dodecylphenyl)-1,1':2',1'':3'',1''':2''',1''''-quinquephenyl
    Compound S8 4-Dodecyl-4',5',6',3''',4''',5''',6'''-heptakis(4-dodecylphenyl)-1,1':2',1'':3'',1''':2''',1''''-quinquephenyl
  5. 4,4''''''-Didodecyl-4',5',6',3''',4''',5''',3''''',4''''',5'''''-octakis(4-dodecylphenyl)-4''',6'''-diphenyl-1,1':2',1'':3'',1''':3''',1'''':3'''',1''''':2''''',1''''''-septiphenyl
    Compound S11 4,4''''''-Didodecyl-4',5',6',3''',4''',5''',3''''',4''''',5'''''-octakis(4-dodecylphenyl)-4''',6'''-diphenyl-1,1':2',1'':3'',1''':3''',1'''':3'''',1''''':2''''',1''''''-septiphenyl

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Author information

Affiliations

  1. Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany

    • Akimitsu Narita,
    • Xinliang Feng,
    • Yenny Hernandez,
    • Søren A. Jensen,
    • Mischa Bonn,
    • Michael Ryan Hansen,
    • Amelie H. R. Koch,
    • George Fytas &
    • Klaus Müllen
  2. FOM Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands

    • Søren A. Jensen
  3. School of Chemistry and Photon Science Institute, Manchester University, Oxford Road, Manchester, M139PL, UK

    • Huafeng Yang &
    • Cinzia Casiraghi
  4. Department of Physics, Free University Berlin, Arnimalle 14, 14195 Berlin, Germany

    • Ivan A. Verzhbitskiy &
    • Cinzia Casiraghi
  5. Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark

    • Michael Ryan Hansen
  6. Department of Materials Science, University of Crete and FORTH, Heraklion, Greece

    • George Fytas
  7. Division of Molecular Imaging and Photonics, Department of Chemistry, KU Leuven Celestijnenlaan, 200 F, B-3001 Leuven, Belgium

    • Oleksandr Ivasenko,
    • Bing Li,
    • Kunal S. Mali,
    • Tatyana Balandina,
    • Sankarapillai Mahesh &
    • Steven De Feyter

Contributions

K.M. and X.F. planned the project. A.N. designed and synthesized all the materials and performed standard characterization, including FTIR analysis. A.N. and Y.H. conducted UV–vis absorption spectroscopic analysis. H.Y., I.A.V. and C.C. carried out Raman spectroscopic analysis. O.I., B.L., K.S.M., T.B. and S.M. performed SPM experiments. S.A.J. conducted the THz spectroscopy experiments. M.R.H carried out solid-state NMR experiments. A.H.R.K. performed laser light-scattering experiments. X.F., M.B., G.F., S.D.F and K.M. supervised the experiments. A.N., S.A.J., C.C., G.F., O.I. and K.S.M. co-wrote the manuscript, and X.F., M.B., S.D.F. and K.M. corrected and finalized it. All authors discussed the results and implications and commented on the manuscript.

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The authors declare no competing financial interests.

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