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Rizzo DJ, Wu M, Tsai HZ, Marangoni T, Durr RA, Omrani AA, Liou F, Bronner C, Joshi T, Nguyen GD, Rodgers GF, Choi WW, Jørgensen JH, Fischer FR, Louie SG, Crommie MF. Length-Dependent Evolution of Type II Heterojunctions in Bottom-Up-Synthesized Graphene Nanoribbons. NANO LETTERS 2019; 19:3221-3228. [PMID: 31002257 DOI: 10.1021/acs.nanolett.9b00758] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The ability to tune the band-edge energies of bottom-up graphene nanoribbons (GNRs) via edge dopants creates new opportunities for designing tailor-made GNR heterojunctions and related nanoscale electronic devices. Here we report the local electronic characterization of type II GNR heterojunctions composed of two different nitrogen edge-doping configurations (carbazole and phenanthridine) that separately exhibit electron-donating and electron-withdrawing behavior. Atomically resolved structural characterization of phenanthridine/carbazole GNR heterojunctions was performed using bond-resolved scanning tunneling microscopy and noncontact atomic force microscopy. Scanning tunneling spectroscopy and first-principles calculations reveal that carbazole and phenanthridine dopant configurations induce opposite upward and downward orbital energy shifts owing to their different electron affinities. The magnitude of the energy offsets observed in carbazole/phenanthridine heterojunctions is dependent on the length of the GNR segments comprising each heterojunction with longer segments leading to larger heterojunction energy offsets. Using a new on-site energy analysis based on Wannier functions, we find that the origin of this behavior is a charge transfer process that reshapes the electrostatic potential profile over a long distance within the GNR heterojunction.
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Zhao L, Kaiser RI, Xu B, Ablikim U, Lu W, Ahmed M, Evseev MM, Bashkirov EK, Azyazov VN, Zagidullin MV, Morozov AN, Howlader AH, Wnuk SF, Mebel AM, Joshi D, Veber G, Fischer FR. Gas phase synthesis of [4]-helicene. Nat Commun 2019; 10:1510. [PMID: 30944302 PMCID: PMC6447558 DOI: 10.1038/s41467-019-09224-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2018] [Accepted: 02/27/2019] [Indexed: 11/29/2022] Open
Abstract
A synthetic route to racemic helicenes via a vinylacetylene mediated gas phase chemistry involving elementary reactions with aryl radicals is presented. In contrast to traditional synthetic routes involving solution chemistry and ionic reaction intermediates, the gas phase synthesis involves a targeted ring annulation involving free radical intermediates. Exploiting the simplest helicene as a benchmark, we show that the gas phase reaction of the 4-phenanthrenyl radical ([C14H9]•) with vinylacetylene (C4H4) yields [4]-helicene (C18H12) along with atomic hydrogen via a low-barrier mechanism through a resonance-stabilized free radical intermediate (C18H13). This pathway may represent a versatile mechanism to build up even more complex polycyclic aromatic hydrocarbons such as [5]- and [6]-helicene via stepwise ring annulation through bimolecular gas phase reactions in circumstellar envelopes of carbon-rich stars, whereas secondary reactions involving hydrogen atom assisted isomerization of thermodynamically less stable isomers of [4]-helicene might be important in combustion flames as well. Helicenes represent key building blocks leading eventually to carbonaceous nanostructures. Here, exploiting [4]-helicene as a benchmark, the authors present a synthetic route to racemic helicenes via a vinylacetylene mediated gas phase chemistry with aryl radicals involving ring annulation.
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Pfeiffer M, Senkovskiy BV, Haberer D, Fischer FR, Yang F, Meerholz K, Ando Y, Grüneis A, Lindfors K. Observation of Room-Temperature Photoluminescence Blinking in Armchair-Edge Graphene Nanoribbons. NANO LETTERS 2018; 18:7038-7044. [PMID: 30336056 DOI: 10.1021/acs.nanolett.8b03006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
By enhancing the photoluminescence from aligned seven-atom wide armchair-edge graphene nanoribbons using plasmonic nanoantennas, we are able to observe blinking of the emission. The on- and off-times of the blinking follow power law statistics. In time-resolved spectra, we observe spectral diffusion. These findings together are a strong indication of the emission originating from a single quantum emitter. The room temperature photoluminescence displays a narrow spectral width of less than 50 meV, which is significantly smaller than the previously observed ensemble line width of 0.8 eV. From spectral time traces, we identify three optical transitions, which are energetically situated below the lowest bulk excitonic state E11 of the nanoribbons. We attribute the emission to transitions involving Tamm states localized at the end of the nanoribbon. The photoluminescence from a single ribbon is strongly enhanced when its end is in the antenna hot spot resulting in the observed single molecule characteristics of the emission. Our findings illustrate the essential role of the end termination of graphene nanoribbons in light emission and allow us to construct a model for photoluminescence from nanoribbons.
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Zhu J, German R, Senkovskiy BV, Haberer D, Fischer FR, Grüneis A, van Loosdrecht PHM. Exciton and phonon dynamics in highly aligned 7-atom wide armchair graphene nanoribbons as seen by time-resolved spontaneous Raman scattering. NANOSCALE 2018; 10:17975-17982. [PMID: 30226260 DOI: 10.1039/c8nr05950k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The opening of a band gap in graphene nanoribbons induces novel optical and electronic properties, strongly enhancing their application potential in nanoscale devices. Knowledge of the optical excitations and associated relaxation dynamics are essential for developing and optimizing device designs and functionality. Here we report on the optical excitations and associated relaxation dynamics in surface aligned 7-atom wide armchair graphene nanoribbons as seen by time-resolved spontaneous Stokes and anti-Stokes Raman scattering spectroscopy. On the anti-Stokes side we observe an optically induced increase of the scattering intensity of the Raman active optical phonons which we assign to changes in the optical phonon populations. The optical phonon population decays with a lifetime of ∼2 ps, indicating an efficient optical-acoustic phonon cooling mechanism. On the Stokes side we observe a substantial decrease of the phonon peak intensities which we relate to the dynamics of the optically induced exciton population. The exciton population shows a multi-exponential relaxation on the hundreds of ps time scale and is independent of the excitation intensity, indicating that exciton-exciton annihilation processes are not important and the exsistence of dark and trapped exciton states. Our results shed light on the optically induced phonon and exciton dynamics in surface aligned armchair graphene nanoribbons and demonstrate that time-resolved spontaneous Raman scattering spectroscopy is a powerful method for exploring quasi-particle dynamics in low dimensional materials.
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Senkovskiy BV, Usachov DY, Fedorov AV, Marangoni T, Haberer D, Tresca C, Profeta G, Caciuc V, Tsukamoto S, Atodiresei N, Ehlen N, Chen C, Avila J, Asensio MC, Varykhalov AY, Nefedov A, Wöll C, Kim TK, Hoesch M, Fischer FR, Grüneis A. Boron-Doped Graphene Nanoribbons: Electronic Structure and Raman Fingerprint. ACS NANO 2018; 12:7571-7582. [PMID: 30004663 DOI: 10.1021/acsnano.8b04125] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We investigate the electronic and vibrational properties of bottom-up synthesized aligned armchair graphene nanoribbons of N = 7 carbon atoms width periodically doped by substitutional boron atoms (B-7AGNRs). Using angle-resolved photoemission spectroscopy and density functional theory calculations, we find that the dopant-derived valence and conduction band states are notably hybridized with electronic states of Au substrate and spread in energy. The interaction with the substrate leaves the bands with pure carbon character rather unperturbed. This results in an identical effective mass of ≈0.2 m0 for the next-highest valence band compared with pristine 7AGNRs. We probe the phonons of B-7AGNRs by ultrahigh-vacuum (UHV) Raman spectroscopy and reveal the existence of characteristic splitting and red shifts in Raman modes due to the presence of substitutional boron atoms. Comparing the Raman spectra for three visible lasers (red, green, and blue), we find that interaction with gold suppresses the Raman signal from B-7AGNRs and the energy of the green laser (2.33 eV) is closer to the resonant E22 transition. The hybridized electronic structure of the B-7AGNR-Au interface is expected to improve electrical characteristics of contacts between graphene nanoribbon and Au. The Raman fingerprint allows the easy identification of B-7AGNRs, which is particularly useful for device fabrication.
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Rizzo DJ, Veber G, Cao T, Bronner C, Chen T, Zhao F, Rodriguez H, Louie SG, Crommie MF, Fischer FR. Topological band engineering of graphene nanoribbons. Nature 2018; 560:204-208. [DOI: 10.1038/s41586-018-0376-8] [Citation(s) in RCA: 342] [Impact Index Per Article: 57.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Accepted: 06/07/2018] [Indexed: 11/09/2022]
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Joshi D, Hauser M, Veber G, Berl A, Xu K, Fischer FR. Super-Resolution Imaging of Clickable Graphene Nanoribbons Decorated with Fluorescent Dyes. J Am Chem Soc 2018; 140:9574-9580. [DOI: 10.1021/jacs.8b04679] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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33
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Pedramrazi Z, Chen C, Zhao F, Cao T, Nguyen GD, Omrani AA, Tsai HZ, Cloke RR, Marangoni T, Rizzo DJ, Joshi T, Bronner C, Choi WW, Fischer FR, Louie SG, Crommie MF. Concentration Dependence of Dopant Electronic Structure in Bottom-up Graphene Nanoribbons. NANO LETTERS 2018; 18:3550-3556. [PMID: 29851493 DOI: 10.1021/acs.nanolett.8b00651] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Bottom-up fabrication techniques enable atomically precise integration of dopant atoms into the structure of graphene nanoribbons (GNRs). Such dopants exhibit perfect alignment within GNRs and behave differently from bulk semiconductor dopants. The effect of dopant concentration on the electronic structure of GNRs, however, remains unclear despite its importance in future electronics applications. Here we use scanning tunneling microscopy and first-principles calculations to investigate the electronic structure of bottom-up synthesized N = 7 armchair GNRs featuring varying concentrations of boron dopants. First-principles calculations of freestanding GNRs predict that the inclusion of boron atoms into a GNR backbone should induce two sharp dopant states whose energy splitting varies with dopant concentration. Scanning tunneling spectroscopy experiments, however, reveal two broad dopant states with an energy splitting greater than expected. This anomalous behavior results from an unusual hybridization between the dopant states and the Au(111) surface, with the dopant-surface interaction strength dictated by the dopant orbital symmetry.
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Passi V, Gahoi A, Senkovskiy BV, Haberer D, Fischer FR, Grüneis A, Lemme MC. Field-Effect Transistors Based on Networks of Highly Aligned, Chemically Synthesized N = 7 Armchair Graphene Nanoribbons. ACS APPLIED MATERIALS & INTERFACES 2018; 10:9900-9903. [PMID: 29516716 PMCID: PMC5880510 DOI: 10.1021/acsami.8b01116] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2018] [Accepted: 03/08/2018] [Indexed: 06/08/2023]
Abstract
We report on the experimental demonstration and electrical characterization of N = 7 armchair graphene nanoribbon (7-AGNR) field effect transistors. The back-gated transistors are fabricated from atomically precise and highly aligned 7-AGNRs, synthesized with a bottom-up approach. The large area transfer process holds the promise of scalable device fabrication with atomically precise nanoribbons. The channels of the FETs are approximately 30 times longer than the average nanoribbon length of 30 nm to 40 nm. The density of the GNRs is high, so that transport can be assumed well-above the percolation threshold. The long channel transistors exhibit a maximum ION/ IOFF current ratio of 87.5.
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Bronner C, Durr RA, Rizzo DJ, Lee YL, Marangoni T, Kalayjian AM, Rodriguez H, Zhao W, Louie SG, Fischer FR, Crommie MF. Hierarchical On-Surface Synthesis of Graphene Nanoribbon Heterojunctions. ACS NANO 2018; 12:2193-2200. [PMID: 29381853 DOI: 10.1021/acsnano.7b08658] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Bottom-up graphene nanoribbon (GNR) heterojunctions are nanoscale strips of graphene whose electronic structure abruptly changes across a covalently bonded interface. Their rational design offers opportunities for profound technological advancements enabled by their extraordinary structural and electronic properties. Thus far, the most critical aspect of their synthesis, the control over sequence and position of heterojunctions along the length of a ribbon, has been plagued by randomness in monomer sequences emerging from step-growth copolymerization of distinct monomers. All bottom-up GNR heterojunction structures created so far have exhibited random sequences of heterojunctions and, while useful for fundamental scientific studies, are difficult to incorporate into functional nanodevices as a result. In contrast, we describe a hierarchical fabrication strategy that allows the growth of bottom-up GNRs that preferentially exhibit a single heterojunction interface rather than a random statistical sequence of junctions along the ribbon. Such heterojunctions provide a viable platform that could be directly used in functional GNR-based device applications at the molecular scale. Our hierarchical GNR fabrication strategy is based on differences in the dissociation energies of C-Br and C-I bonds that allow control over the growth sequence of the block copolymers from which GNRs are formed and consequently yields a significantly higher proportion of single-junction GNR heterostructures. Scanning tunneling spectroscopy and density functional theory calculations confirm that hierarchically grown heterojunctions between chevron GNR (cGNR) and binaphthyl-cGNR segments exhibit straddling Type I band alignment in structures that are only one atomic layer thick and 3 nm in width.
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Durr RA, Haberer D, Lee YL, Blackwell R, Kalayjian AM, Marangoni T, Ihm J, Louie SG, Fischer FR. Orbitally Matched Edge-Doping in Graphene Nanoribbons. J Am Chem Soc 2018; 140:807-813. [DOI: 10.1021/jacs.7b11886] [Citation(s) in RCA: 54] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Perkins W, Fischer FR. Inserting Porphyrin Quantum Dots in Bottom‐Up Synthesized Graphene Nanoribbons. Chemistry 2017; 23:17687-17691. [DOI: 10.1002/chem.201705252] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2017] [Indexed: 11/08/2022]
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38
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Nguyen GD, Tsai HZ, Omrani AA, Marangoni T, Wu M, Rizzo DJ, Rodgers GF, Cloke RR, Durr RA, Sakai Y, Liou F, Aikawa AS, Chelikowsky JR, Louie SG, Fischer FR, Crommie MF. Atomically precise graphene nanoribbon heterojunctions from a single molecular precursor. NATURE NANOTECHNOLOGY 2017; 12:1077-1082. [PMID: 28945240 DOI: 10.1038/nnano.2017.155] [Citation(s) in RCA: 103] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2016] [Accepted: 07/04/2017] [Indexed: 05/22/2023]
Abstract
The rational bottom-up synthesis of atomically defined graphene nanoribbon (GNR) heterojunctions represents an enabling technology for the design of nanoscale electronic devices. Synthetic strategies used thus far have relied on the random copolymerization of two electronically distinct molecular precursors to yield GNR heterojunctions. Here we report the fabrication and electronic characterization of atomically precise GNR heterojunctions prepared through late-stage functionalization of chevron GNRs obtained from a single precursor. Post-growth excitation of fully cyclized GNRs induces cleavage of sacrificial carbonyl groups, resulting in atomically well-defined heterojunctions within a single GNR. The GNR heterojunction structure was characterized using bond-resolved scanning tunnelling microscopy, which enables chemical bond imaging at T = 4.5 K. Scanning tunnelling spectroscopy reveals that band alignment across the heterojunction interface yields a type II heterojunction, in agreement with first-principles calculations. GNR heterojunction band realignment proceeds over a distance less than 1 nm, leading to extremely large effective fields.
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Jeong H, von Kugelgen S, Bellone D, Fischer FR. Regioselective Termination Reagents for Ring-Opening Alkyne Metathesis Polymerization. J Am Chem Soc 2017; 139:15509-15514. [DOI: 10.1021/jacs.7b09390] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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40
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Senkovskiy BV, Pfeiffer M, Alavi SK, Bliesener A, Zhu J, Michel S, Fedorov AV, German R, Hertel D, Haberer D, Petaccia L, Fischer FR, Meerholz K, van Loosdrecht PHM, Lindfors K, Grüneis A. Making Graphene Nanoribbons Photoluminescent. NANO LETTERS 2017; 17:4029-4037. [PMID: 28358214 DOI: 10.1021/acs.nanolett.7b00147] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We demonstrate the alignment-preserving transfer of parallel graphene nanoribbons (GNRs) onto insulating substrates. The photophysics of such samples is characterized by polarized Raman and photoluminescence (PL) spectroscopies. The Raman scattered light and the PL are polarized along the GNR axis. The Raman cross section as a function of excitation energy has distinct excitonic peaks associated with transitions between the one-dimensional parabolic subbands. We find that the PL of GNRs is intrinsically low but can be strongly enhanced by blue laser irradiation in ambient conditions or hydrogenation in ultrahigh vacuum. These functionalization routes cause the formation of sp3 defects in GNRs. We demonstrate the laser writing of luminescent patterns in GNR films for maskless lithography by the controlled generation of defects. Our findings set the stage for further exploration of the optical properties of GNRs on insulating substrates and in device geometries.
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von Kugelgen S, Sifri R, Bellone D, Fischer FR. Regioselective Carbyne Transfer to Ring-Opening Alkyne Metathesis Initiators Gives Access to Telechelic Polymers. J Am Chem Soc 2017; 139:7577-7585. [DOI: 10.1021/jacs.7b02225] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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42
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Rogers C, Perkins WS, Veber G, Williams TE, Cloke RR, Fischer FR. Synergistic Enhancement of Electrocatalytic CO2 Reduction with Gold Nanoparticles Embedded in Functional Graphene Nanoribbon Composite Electrodes. J Am Chem Soc 2017; 139:4052-4061. [DOI: 10.1021/jacs.6b12217] [Citation(s) in RCA: 192] [Impact Index Per Article: 27.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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43
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de Oteyza DG, Pérez Paz A, Chen YC, Pedramrazi Z, Riss A, Wickenburg S, Tsai HZ, Fischer FR, Crommie MF, Rubio A. Noncovalent Dimerization after Enediyne Cyclization on Au(111). J Am Chem Soc 2016; 138:10963-7. [PMID: 27490459 DOI: 10.1021/jacs.6b05203] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We investigate the thermally induced cyclization of 1,2-bis(2-phenylethynyl)benzene on Au(111) using scanning tunneling microscopy and computer simulations. Cyclization of sterically hindered enediynes is known to proceed via two competing mechanisms in solution: a classic C(1)-C(6) (Bergman) or a C(1)-C(5) cyclization pathway. On Au(111), we find that the C(1)-C(5) cyclization is suppressed and that the C(1)-C(6) cyclization yields a highly strained bicyclic olefin whose surface chemistry was hitherto unknown. The C(1)-C(6) product self-assembles into discrete noncovalently bound dimers on the surface. The reaction mechanism and driving forces behind noncovalent association are discussed in light of density functional theory calculations.
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Marangoni T, Haberer D, Rizzo DJ, Cloke RR, Fischer FR. Heterostructures through Divergent Edge Reconstruction in Nitrogen‐Doped Segmented Graphene Nanoribbons. Chemistry 2016; 22:13037-40. [DOI: 10.1002/chem.201603497] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Indexed: 11/08/2022]
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von Kugelgen S, Bellone DE, Cloke RR, Perkins WS, Fischer FR. Initiator Control of Conjugated Polymer Topology in Ring-Opening Alkyne Metathesis Polymerization. J Am Chem Soc 2016; 138:6234-9. [PMID: 27120088 DOI: 10.1021/jacs.6b02422] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Molybdenum carbyne complexes [RC≡Mo(OC(CH3)(CF3)2)3] featuring a mesityl (R = Mes) or an ethyl (R = Et) substituent initiate the living ring-opening alkyne metathesis polymerization of the strained cyclic alkyne, 5,6,11,12-tetradehydrobenzo[a,e][8]annulene, to yield fully conjugated poly(o-phenylene ethynylene). The difference in the steric demand of the polymer end-group (Mes vs Et) transferred during the initiation step determines the topology of the resulting polymer chain. While [MesC≡Mo(OC(CH3)(CF3)2)3] exclusively yields linear poly(o-phenylene ethynylene), polymerization initiated by [EtC≡Mo(OC(CH3)(CF3)2)3] results in cyclic polymers ranging in size from n = 5 to 20 monomer units. Kinetic studies reveal that the propagating species emerging from [EtC≡Mo(OC(CH3)(CF3)2)3] undergoes a highly selective intramolecular backbiting into the butynyl end-group.
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Fischer FR. Profile: Early Excellence in Physical Organic Chemistry. J PHYS ORG CHEM 2015. [DOI: 10.1002/poc.3466] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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47
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Rogers C, Chen C, Pedramrazi Z, Omrani AA, Tsai H, Jung HS, Lin S, Crommie MF, Fischer FR. Closing the Nanographene Gap: Surface‐Assisted Synthesis of Peripentacene from 6,6′‐Bipentacene Precursors. Angew Chem Int Ed Engl 2015. [DOI: 10.1002/ange.201507104] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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48
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Rogers C, Chen C, Pedramrazi Z, Omrani AA, Tsai HZ, Jung HS, Lin S, Crommie MF, Fischer FR. Closing the Nanographene Gap: Surface-Assisted Synthesis of Peripentacene from 6,6′-Bipentacene Precursors. Angew Chem Int Ed Engl 2015; 54:15143-6. [DOI: 10.1002/anie.201507104] [Citation(s) in RCA: 105] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Revised: 09/08/2015] [Indexed: 11/09/2022]
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49
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Cloke RR, Marangoni T, Nguyen GD, Joshi T, Rizzo DJ, Bronner C, Cao T, Louie SG, Crommie MF, Fischer FR. Site-Specific Substitutional Boron Doping of Semiconducting Armchair Graphene Nanoribbons. J Am Chem Soc 2015; 137:8872-5. [DOI: 10.1021/jacs.5b02523] [Citation(s) in RCA: 185] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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50
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Chen YC, Cao T, Chen C, Pedramrazi Z, Haberer D, de Oteyza DG, Fischer FR, Louie SG, Crommie MF. Molecular bandgap engineering of bottom-up synthesized graphene nanoribbon heterojunctions. NATURE NANOTECHNOLOGY 2015; 10:156-60. [PMID: 25581888 DOI: 10.1038/nnano.2014.307] [Citation(s) in RCA: 221] [Impact Index Per Article: 24.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2014] [Accepted: 11/19/2014] [Indexed: 05/22/2023]
Abstract
Bandgap engineering is used to create semiconductor heterostructure devices that perform processes such as resonant tunnelling and solar energy conversion. However, the performance of such devices degrades as their size is reduced. Graphene-based molecular electronics has emerged as a candidate to enable high performance down to the single-molecule scale. Graphene nanoribbons, for example, can have widths of less than 2 nm and bandgaps that are tunable via their width and symmetry. It has been predicted that bandgap engineering within a single graphene nanoribbon may be achieved by varying the width of covalently bonded segments within the nanoribbon. Here, we demonstrate the bottom-up synthesis of such width-modulated armchair graphene nanoribbon heterostructures, obtained by fusing segments made from two different molecular building blocks. We study these heterojunctions at subnanometre length scales with scanning tunnelling microscopy and spectroscopy, and identify their spatially modulated electronic structure, demonstrating molecular-scale bandgap engineering, including type I heterojunction behaviour. First-principles calculations support these findings and provide insight into the microscopic electronic structure of bandgap-engineered graphene nanoribbon heterojunctions.
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