Co-reporter:Mingguang Chen, Xiaojuan Tian, Wangxiang Li, Elena Bekyarova, Guanghui Li, Matthew Moser, and Robert C. Haddon
Chemistry of Materials 2016 Volume 28(Issue 7) pp:2260
Publication Date(Web):March 12, 2016
DOI:10.1021/acs.chemmater.6b00217
The formation of bis-hexahapto bonds between graphitic surfaces can electronically interconnect the surfaces of carbon materials containing the polybenzenoid ring system and increase the conductivity without introducing a strong perturbation to the in-plane electronic structure. In this paper, we report the use of organometallic chemistry to interconnect the surfaces of small scale graphene nanoplatelets by using a variety of metals and photochemically activated organometallic reagents.
Co-reporter:Robert C. Haddon, Ziqi Tian, and De-en Jiang
The Journal of Organic Chemistry 2016 Volume 81(Issue 9) pp:3648-3653
Publication Date(Web):April 11, 2016
DOI:10.1021/acs.joc.6b00298
The Hammond Postulate and the Leffler analysis have provided a cornerstone in the understanding of reaction processes in organic chemistry for over 60 years, yet quantitative applications of these methodologies over the range of reactions envisaged in the original works remain elusive. In the present paper, we analyze a series of SN2 reactions in three solvents that lead to endothermic and exothermic reaction processes, and we show that within the hybridization reaction coordinate the SN2 reaction is fully consistent with both treatments. We give new presentations of the reaction energies as a function of reaction progress, which allow the generation of unified reaction coordinate diagrams that show a linear relationship between the hybridization metric of reaction progress and the relative energies of the stationary points on the potential surface as a function of structure and solvent as originally envisaged by Leffler and Hammond.
Co-reporter:Mikhail E. Itkis, Aron Pekker, Xiaojuan Tian, Elena Bekyarova, and Robert C. Haddon
Accounts of Chemical Research 2015 Volume 48(Issue 8) pp:2270
Publication Date(Web):August 5, 2015
DOI:10.1021/acs.accounts.5b00107
Single-walled carbon nanotube (SWNT) thin films provide a unique platform for the development of electronic and photonic devices because they combine the advantages of the outstanding physical properties of individual SWNTs with the capabilities of large area thin film manufacturing and patterning technologies. Flexible SWNT thin film based field-effect transistors, sensors, detectors, photovoltaic cells, and light emitting diodes have been already demonstrated, and SWNT thin film transparent, conductive coatings for large area displays and smart windows are under development. While chirally pure SWNTs are not yet commercially available, the marketing of semiconducting (SC) and metallic (MT) SWNTs has facilitated progress toward applications by making available materials of consistent electronic structure. Nevertheless the electrical transport properties of networks of separated SWNTs are inferior to those of individual SWNTs. In particular, for semiconducting SWNTs, which are the subject of this Account, the electrical transport drastically differs from the behavior of traditional semiconductors: for example, the bandgap of germanium (E = 0.66 eV) roughly matches that of individual SC-SWNTs of diameter 1.5 nm, but in the range 300–100 K, the intrinsic carrier concentration in Ge decreases by more than 10 orders of magnitude while the conductivity of a typical SC-SWNT network decreases by less than a factor of 4. Clearly this weak modulation of the conductivity hinders the application of SC-SWNT films as field effect transistors and photodetectors, and it is the purpose of this Account to analyze the mechanism of the electrical transport leading to the unusually weak temperature dependence of the electrical conductivity of such networks. Extrinsic factors such as the contribution of residual amounts of MT-SWNTs arising from incomplete separation and doping of SWNTs are evaluated. However, the observed temperature dependence of the conductivity indicates the presence of midgap electronic states in the semiconducting SWNTs, which provide a source of low-energy excitations, which can contribute to hopping conductance along the nanotubes following fluctuation induced tunneling across the internanotube junctions, which together dominate the low temperature transport and limit the resistivity of the films. At high temperatures, the intrinsic carriers thermally activated across the bandgap as in a traditional semiconductor became available for band transport. The midgap states pin the Fermi level to the middle of the bandgap, and their origin is ascribed to defects in the SWNT walls. The presence of such midgap states has been reported in connection with scanning tunneling spectroscopy experiments, Coulomb blockade observations in low temperature electrical measurements, selective electrochemical deposition imaging, tip-enhanced Raman spectroscopy, high resolution photocurrent spectroscopy, and the modeling of the electronic density of states associated with various defects.Midgap states are present in conventional semiconductors, but what is unusual in the present context is the extent of their contribution to the electrical transport in networks of semiconducting SWNTs. In this Account, we sharpen the focus on the midgap states in SC-SWNTs, their effect on the electronic properties of SC-SWNT networks, and the importance of these effects on efforts to develop electronic and photonic applications of SC-SWNTs.
Co-reporter:Guanghui Li; Chengyin Fu; M. Belén Oviedo; Mingguang Chen; Xiaojuan Tian; Elena Bekyarova; Mikhail E. Itkis; Bryan M. Wong; Juchen Guo;Robert C. Haddon
Journal of the American Chemical Society 2015 Volume 138(Issue 1) pp:40-43
Publication Date(Web):December 16, 2015
DOI:10.1021/jacs.5b10598
Encapsulation of sulfur in HiPCO-SWNTs leads to large changes in the Raman spectra with the appearance of new peaks at 319, 395, and 715 cm–1 which originate from the sulfur species within the SWNTs, while the high frequency SWNT bands (ν > 1200 cm–1) are decreased in intensity. The encapsulated species also shifts the near-IR interband electronic transitions to lower energy by more than 10%. These effects seem to originate with the van der Waals interaction of the confined sulfur species with the walls of the SWNTs which are not expected to be significant in the case of the previously studied large diameter SWNTs. We suggest that sulfur in the small diameter SWNTs exists as a helical polymeric sulfur chain that enters the SWNT interior in the form of S2 (3Σg–) molecules which undergo polymerization to linear diradicals.
Co-reporter:Pradip Bag; Mikhail E. Itkis; Dejan Stekovic; Sushanta K. Pal; Fook S. Tham;Robert C. Haddon
Journal of the American Chemical Society 2015 Volume 137(Issue 31) pp:10000-10008
Publication Date(Web):August 3, 2015
DOI:10.1021/jacs.5b06145
We report the substitutional doping of solid-state spiro-bis(5-methyl-1,9-oxido-phenalenyl)boron radical ([2]2B) by co-crystallization of this radical with the corresponding spiro-bis(5-methyl-1,9-oxido-phenalenyl)beryllium compound ([2]2Be). The pure compounds crystallize in different space groups ([2]2B, P1̅, Z = 2; [2]2Be, P21/c, Z = 4) with distinct packing arrangements, yet we are able to isolate crystals of composition [2]2B(1–x)Bex, where x = 0–0.59. The phase transition from the P1̅ to the P21/c space group occurs at x = 0.1, but the conductivities of the solid solutions are enhanced and the activation energies reduced for values of x = 0–0.25. The molecular packing is driven by the relative concentration of the spin-bearing ([2]2B) and spin-free ([2]2Be) molecules in the crystals, and the extended Hückel theory band structures show that the progressive incorporation of spin-free [2]2Be in the lattice of the [2]2B radical (overall bandwidth, W = 1.4 eV, in the pure compound) leads to very strong narrowing of the bandwidth, which reaches a minimum at [2]2Be (W = 0.3 eV). The results provide a graphic picture of the structural transformations undergone by the lattice, and at certain compositions we are able to identify distinct structures for the [2]2B and [2]2Be molecules in a single crystalline phase.
Co-reporter:Aron Pekker, Mingguang Chen, Elena Bekyarova and Robert C. Haddon
Materials Horizons 2015 vol. 2(Issue 1) pp:81-85
Publication Date(Web):17 Nov 2014
DOI:10.1039/C4MH00192C
The electrical conductivity of single-walled carbon nanotube (SWNT) networks is strongly enhanced by the high vacuum e-beam deposition of transition metals. In the present communication we demonstrate that it is possible to accomplish the same chemical functionalization reactions at room temperature beginning with simple organometallic precursors. We show that the photochemically induced reactions of solutions of Cr(CO)6, Cr(η6-benzene)(CO)3, and Cr(η6-benzene)2 with thin films of semiconducting, metallic and non-separated SWNT films all lead to strongly enhanced conductivities which produce consistent results for each SWNT type among the three organometallic reagents. We conclude that all three of these reactions lead to the generation of covalent (η6-SWNT)Cr(η6-SWNT) interconnects which provide conducting pathways in the SWNT films and our results broaden the applicability of the transition metal bis-hexahapto-bond as an electronically conjugating linkage between graphene surfaces.
Co-reporter:Matthew L. Moser, Aron Pekker, Xiaojuan Tian, Elena Bekyarova, Mikhail E Itkis, and Robert C Haddon
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 51) pp:28013
Publication Date(Web):April 23, 2015
DOI:10.1021/acsami.5b00942
We spectroscopically analyze the effect of e-beam deposition of lanthanide metals on the electronic structure and conductivities of films of semiconducting (SC) single-walled carbon nanotubes (SWNTs) in high vacuum. We employ near-infrared and Raman spectroscopy to interpret the changes in the electronic structure of SWNTs on exposure to small amounts of the lanthanides (Ln = Sm, Eu, Gd, Dy, Ho, Yb), based on the behavior of the reference metals (M = Li, Cr) which are taken to exemplify ionic and covalent bonding, respectively. The analysis shows that while the lanthanides are more electropositive than the transition metals, in most cases they exhibit similar conductivity behavior which we interpret in terms of the formation of covalent bis-hexahapto bonds [(η6-SWNT)M(η6-SWNT), where M = La, Nd, Gd, Dy, Ho]. However, only M = Eu, Sm, Yb show the continually increasing conductivity characteristic of Li, and this supports our contention that these metals provide the first examples of mixed covalent–ionic bis-hexahapto bonds [(η6-SWNT)M(η6-SWNT), where M = Sm, Eu, Yb].Keywords: carbon nanotube film; conductivity; lanthanides; optical properties; organometallic
Co-reporter:Elena B. Bekyarova, Sandip Niyogi, Santanu Sarkar, Xiaojuan Tian, Mingguang Chen, Matthew L. Moser, Kurshid Ayub, Reginald H. Mitchell, Robert C. Haddon
Synthetic Metals 2015 Volume 210(Part A) pp:80-84
Publication Date(Web):December 2015
DOI:10.1016/j.synthmet.2015.07.004
•Covalent chemistry affects the geometric and electronic structure of functionalized graphene.•Addition chemistry leads to σ-bonds to graphene surfaces and removes C-atoms from conjugation.•Hexahapto-metal bond preserves the graphitic band structure-constructive rehybridization.We consider the covalent chemistry of the carbon allotropes with an emphasis on the newest member—graphene. We focus on the effect of such chemistry on the geometric and electronic structure of the functionalized materials and the way in which the conjugation is modified by such processes. We conclude that there are two limiting cases: (a) Conventional addition chemistry leading to the formation of σ-bonds to the graphitic surface in which there is full rehybridization of the derivatized carbon atoms from sp2 to sp3; thus these carbon atoms are effectively removed from conjugation and from the electronic band structure (referred to as destructive rehybridization). (b) Covalent chemisorption with formation of an organometallic hexahapto-metal bond that largely preserves the graphitic band structure (constructive rehybridization) and accompanies the formation of bis-hexahapto-metal bonds such as those in (η6-SWNT)Cr(η6-SWNT) which serve to interconnect adjacent graphitic surfaces and significantly reduces the internanotube junction resistance in SWNT networks. The formation of η2 di-hapto bonds represent an intermediate case of covalent chemistry and is known to be important in carbon nanotubes and particularly the fullerenes but this situation has been treated in detail in previous publications.
Co-reporter:Irina Kalinina, Yas Fadel Al-Hadeethi, Elena Bekyarova, Chao Zhao, Qingxiao Wang, Xixiang Zhang, Ali Al-Zahrani, Faisal Al-Agel, Fahad Al-Marzouki, Robert C. Haddon
Materials Letters 2015 Volume 142() pp:312-316
Publication Date(Web):1 March 2015
DOI:10.1016/j.matlet.2014.11.157
•Solution phase synthesis leads to Cr-clusters attached to carbon nanotube walls.•The size of Cr-clusters in Cr-complexed SWNTs is controlled by the reaction time.•Organometallic complexation extends the dimensionality of graphitic surfaces.The solution phase reactions of single-walled carbon nanotubes (SWNTs) with Cr(CO)6 and benzene-Cr(CO)3 can lead to the formation of small chromium clusters. The cluster size can be varied from less than 1 nm to about 4 nm by increasing the reaction time. TEM images suggest that the clusters are deposited predominantly on the exterior walls of the nanotubes. TGA analysis was used to obtain the Cr content and carbon to chromium ratio in the Cr-complexed SWNTs. It is suggested that the carbon nanotube benzenoid structure templates the condensation of chromium atoms and facilitates the loss of carbon monoxide leading to well defined metal clusters.
Co-reporter:Xiaojuan Tian, Matthew L. Moser, Aron Pekker, Santanu Sarkar, Jason Ramirez, Elena Bekyarova, Mikhail E. Itkis, and Robert C. Haddon
Nano Letters 2014 Volume 14(Issue 7) pp:3930-3937
Publication Date(Web):June 3, 2014
DOI:10.1021/nl501212u
The formation of covalent bonds to single-walled carbon nanotube (SWNT) or graphene surfaces usually leads to a decrease in the electrical conductivity and mobility as a result of the structural rehybridization of the functionalized carbon atoms from sp2 to sp3. In the present study, we explore the effect of metal deposition on semiconducting (SC-) and metallic (MT-) SWNT thin films in the vicinity of the percolation threshold and we are able to clearly delineate the effects of weak physisorption, ionic chemisorption with charge transfer, and covalent hexahapto (η6) chemisorption on these percolating networks. The results support the idea that for those metals capable of forming bis-hexahapto-bonds, the generation of covalent (η6-SWNT)M(η6-SWNT) interconnects provides a conducting pathway in the SWNT films and establishes the transition metal bis-hexahapto organometallic bond as an electronically conjugating linkage between graphene surfaces.
Co-reporter:Sushanta K. Pal ; Pradip Bag ; Mikhail E. Itkis ; Fook S. Tham ;Robert C. Haddon
Journal of the American Chemical Society 2014 Volume 136(Issue 42) pp:14738-14741
Publication Date(Web):October 1, 2014
DOI:10.1021/ja508903z
We report the crystallization of a subsitutionally doped organic conductor based on a host lattice composed of spiro-bis(phenalenyl)boron radicals. Co-crystallization of solutions of spiro-bis(9-oxidophenalenone)boron radical [PLY(O,O)]2B mixed with selected amounts of spiro-bis(9-oxidophenalenone)beryllium [PLY(O,O)]2Be leads to the formation of a series of solid-state solutions of composition [PLY(O,O)]2B(1–x)Bex. The dopant molecules [PLY(O,O)]2Be serve to introduce holes into the lattice of spins provided by the [PLY(O,O)]2B radicals and lead to a systematic increase in the conductivity while decreasing the activation energy of the conduction process and leaving the solid-state structure relatively unperturbed. While the energies of the hole sites are expected to be high, the results are consistent with the interpretation of the electronic structure of [PLY(O,O)]2B in terms of the resonating valence bond model.
Co-reporter:Santanu Sarkar, Matthew L. Moser, Xiaojuan Tian, Xixiang Zhang, Yas Fadel Al-Hadeethi, and Robert C. Haddon
Chemistry of Materials 2014 Volume 26(Issue 1) pp:184
Publication Date(Web):September 3, 2013
DOI:10.1021/cm4025809
In this Perspective, we present an overview of recent fundamental studies on the nature of the interaction between individual metal atoms and metal clusters and the conjugated surfaces of graphene and carbon nanotube with a particular focus on the electronic structure and chemical bonding at the metal–graphene interface. We discuss the relevance of organometallic complexes of graphitic materials to the development of a fundamental understanding of these interactions and their application in atomtronics as atomic interconnects, high mobility organometallic transistor devices, high-frequency electronic devices, organometallic catalysis (hydrogen fuel generation by photocatalytic water splitting, fuel cells, hydrogenation), spintronics, memory devices, and the next generation energy devices. We touch on chemical vapor deposition (CVD) graphene grown on metals, the reactivity of its surface, and its use as a template for asymmetric graphene functionalization chemistry (ultrathin Janus discs). We highlight some of the latest advances in understanding the nature of interactions between metals and graphene surfaces from the standpoint of metal overlayers deposited on graphene and SWNT thin films. Finally, we comment on the major challenges facing the field and the opportunities for technological applications.Keywords: asymmetric chemistry; atomtronics; energy conversion; fuel cells; hexahapto bonding; hydrogen fuel; interconnects; Janus graphene; organometallic chemistry; water splitting;
Co-reporter:Xiaojuan Tian, Santanu Sarkar, Aron Pekker, Matthew L. Moser, Irina Kalinina, Elena Bekyarova, Mikhail E. Itkis, Robert C. Haddon
Carbon 2014 Volume 72() pp:82-88
Publication Date(Web):June 2014
DOI:10.1016/j.carbon.2014.01.054
With the advent of many different forms of graphene (in addition to the long standing interest in fullerenes and carbon nanotubes), the characterization of carbon materials and their degree of conjugation is a particularly important topic in carbon science. We report the application of absorption spectroscopy and conductivity measurements to graphene derivatives and related carbon materials. Reduced graphene oxide (RGO) has been widely studied as a promising material for graphene applications because of its processability, and the same considerations apply to graphene functionalized with octadecylamine (ODA). This study utilizes a direct chemical modification of GO with ODA in the presence of dicyclohexylcarbodiimide to partially regenerate the graphene π-conjugation while producing a material (ODA-G) with excellent solubility in organic solvents. We show that the ODA-G exhibits optical absorptions, which are much stronger than those of GO, and comparable to liquid phase exfoliated graphene and reduced graphene oxide; the optical analysis is unified by the development of an analytical relationship between solid state absorption coefficients and solution state extinction coefficients, which allows the direct comparison of the electronic absorption spectroscopy of films and solutions of carbon materials. We further benchmark the regeneration of the graphenic structure in ODA-G with electrical conductivity measurements.
Co-reporter:Matthew L. Moser, Xiaojuan Tian, Aron Pekker, Santanu Sarkar, Elena Bekyarova, Mikhail E. Itkis and Robert C. Haddon
Dalton Transactions 2014 vol. 43(Issue 20) pp:7379-7382
Publication Date(Web):20 Feb 2014
DOI:10.1039/C3DT53291G
We report the response of the electrical conductivity of semiconducting single-walled carbon nanotube (SWNT) thin films on exposure to metal vapors of the early lanthanides under high vacuum conditions. We attribute the strongly enhanced conductivities observed on deposition of samarium and europium to charge transfer from the metals to the SWNT backbone, thereby leading to the first examples of mixed covalent–ionic bis-hexahapto bonds [(η6-SWNT)M(η6-SWNT), where M = Sm, Eu].
Co-reporter:Manoj K. Gottipati, Josheua J. Samuelson, Irina Kalinina, Elena Bekyarova, Robert C. Haddon, and Vladimir Parpura
Nano Letters 2013 Volume 13(Issue 9) pp:4387-4392
Publication Date(Web):August 12, 2013
DOI:10.1021/nl402226z
We used single-walled carbon nanotube (CNT) films to modulate the morpho-functional and proliferative characteristics of astrocytes. When plated on the CNT films of various thicknesses, astrocytes grow bigger and rounder in shape with a decrease in the immunoreactivity of glial fibrillary acidic protein along with an increase in their proliferation, changes associated with the dedifferentiation of astrocytes in culture. Thus, CNT films, as a coating material for electrodes used in brain machine interface, could reduce astrogliosis around the site of implantation.
Co-reporter:Pradip Bag ; Sushanta K. Pal ; Mikhail E. Itkis ; Arindam Sarkar ; Fook S. Tham ; Bruno Donnadieu ;Robert C. Haddon
Journal of the American Chemical Society 2013 Volume 135(Issue 35) pp:12936-12939
Publication Date(Web):August 19, 2013
DOI:10.1021/ja405814f
We report the synthesis and properties of a series of spiro-bis(3,4,6,7-tetrachalcogenide-substituted-phenalenyl)boron salts and two of the corresponding tetrathioalkyl-substituted spiro-bis(phenalenyl)boron radicals [tetrathiomethyl (10) and tetrathioethyl (11)] in which all of the active positions of the phenalenyl (PLY) nucleus are functionalized. In the solid state, radicals 10 and 11 exist as a weak π-dimers due to the steric congestion of the thioalkyl groups in the superimposed PLY units. As a result, the spins are localized in the isolated (nonsuperimposed) PLY rings, and the structure, magnetic susceptibility measurements, and band structure calculations confirm that these PLY units are unable to undergo strong intermolecular interaction as a result of the orientation of the thioalkyl groups.
Co-reporter:Pradip Bag, Fook S. Tham, Bruno Donnadieu, and Robert C. Haddon
Organic Letters 2013 Volume 15(Issue 6) pp:1198-1201
Publication Date(Web):March 6, 2013
DOI:10.1021/ol400452f
Preparations of two hexathiophenalenylium compounds as stable salts from the reaction of 3,4,6,7-tetrathio-9-hydroxyphenalenone with Lawesson’s reagent have been reported. The presence of three disulfide linkages on the periphery of the core phenalenyl unit is confirmed by X-ray crystallographic characterizations. Electrochemical cell potentials are lower than those of related dithio- and tetrathio-bridged phenalenyl radicals, and the hexathiophenalenyl radical shows a strong electron paramagnetic resonance (EPR) signal in the solid state.
Co-reporter:Neetu Jha;Palanisamy Ramesh;Elena Bekyarova;Mikhail E. Itkis;Robert C. Haddon
Advanced Energy Materials 2012 Volume 2( Issue 4) pp:438-444
Publication Date(Web):
DOI:10.1002/aenm.201100697
Abstract
A high energy density supercapacitor device is reported that utilizes hybrid carbon electrodes and the ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) as an electrolyte. The hybrid electrodes are prepared from reduced graphite oxide (rGO) and purified single-walled carbon nanotubes (SWCNTs). A simple casting technique gives the hybrid structure with optimum porosity and functionality that provides high energy and power densities. The combination of SWCNTs and rGO in a weight ratio of 1:1 is found to afford a specific capacitance of 222 F g−1 and an energy density of 94 Wh kg−1 at room temperature.
Co-reporter:Arindam Sarkar, Sushanta K. Pal, Mikhail E. Itkis, Fook S. Tham and Robert C. Haddon
Journal of Materials Chemistry A 2012 vol. 22(Issue 17) pp:8245-8256
Publication Date(Web):16 Mar 2012
DOI:10.1039/C2JM16001C
We report a synthetic scheme for the preparation of alkylthio, dithio-bridged and diseleno-bridged 9-hydroxyphenalenones and associated spiro-biphenalenyl boron neutral radicals. We show that the strategy of sulfur substitution at the active positions of the phenalenyl units reduces the electrochemical disproportionation potential (ΔE2−1 = E2½ − E1½, where E1½ and E2½ are the first and second reduction potentials of corresponding cations) of the alkylthio-radicals [3,7-SR-PLY(O,O)]2B, (R = Me, 9), (R = Et, 10) and (R = Pr, 11), but brings about a significant reduction of the ΔE2−1 value in the case of disulfide and diselenide substitution, [3,4-S,S-PLY(O,O)]2B (12) and [3,4-Se,Se-PLY(O,O)]2B (13). The crystal structures of 10 and 11 show that the radicals exist as one dimensional (1-D) π-chains of superimposed phenalenyl units, and the molecular units pack more efficiently than the oxygen-substituted analog [3,7-OMe-PLY(O,O)]2B (8). Magnetic susceptibility measurements indicate that in the solid state the radicals remain paramagnetic while there is spin–spin interaction between the molecules along the π-chains. Band structure calculations are in accordance with the magnetic measurement data and indicate the presence of interactions between the molecules. The room temperature electrical conductivities of both compounds are found to be σRT = 1.5 × 10−2 S cm−1.
Co-reporter:Irina Kalinina;Elena Bekyarova;Santanu Sarkar;Feihu Wang;Mikhail E. Itkis;Xiaojuan Tian;Sip Niyogi;Neetu Jha ;Robert C. Haddon
Macromolecular Chemistry and Physics 2012 Volume 213( Issue 10-11) pp:1001-1019
Publication Date(Web):
DOI:10.1002/macp.201100661
Abstract
We report the preparation of organometallic side-wall complexes of single-walled carbon nanotubes (SWNTs) under conditions, which allow the study of both mono- and bis-hexahapto SWNT coordination compounds [(η6-SWNT)Cr(CO)3, (η6-SWNT)Cr(η6-C6H6), (η6-SWNT)2Cr]. The results are interpreted in terms of exohedral and endohedral binding of chromium to the SWNT sidewalls and ligand competition reactions suggest that endohedral binding provides a very stable and kinetically inert mode of organometallic bonding. We demonstrate that the electrical conductivity of SWNT thin films are significantly enhanced by side-wall bonding to Group 6 transition metals (M = Cr, Mo, and W), which serve to reduce the inter-carbon nanotube junction electrical resistance by the formation of SWNT interconnects [(η6-SWNT)2M].
Co-reporter:Feihu Wang;Mikhail E. Itkis;Elena Bekyarova;Santanu Sarkar;Xiaojuan Tian;Robert C Haddon
Journal of Physical Organic Chemistry 2012 Volume 25( Issue 7) pp:607-610
Publication Date(Web):
DOI:10.1002/poc.1959
We report the effect of transition metal deposition on the conductivity of single-walled carbon nanotube (SWNT) networks. The slow evaporation of small amounts of highly mobile transition metal atoms significantly reduces the resistance of SWNT thin films; we suggest that Cr, Fe, and Ti atoms form bis-hexahapto complexes at the SWNT sidewalls, thereby bridging adjacent carbon nanotubes and reducing the inter-nanotube junction resistance. Copyright © 2012 John Wiley & Sons, Ltd.
Co-reporter:Pradip Bag;Mikhail E. Itkis;Sushanta K. Pal;Elena Bekyarova;Bruno Donnadieu;Robert C. Haddon
Journal of Physical Organic Chemistry 2012 Volume 25( Issue 7) pp:566-573
Publication Date(Web):
DOI:10.1002/poc.2906
We report the preparation, crystallization, and solid state characterization of a new benzannulated phenalenyl radical; a distinctive feature of this molecular solid is the absence of any well defined conducting pathway(s). In the solid state, the radicals exist as π-dimer and the requisite C···C contacts between dimers are all larger than the sum of the van der Waals distances. The magnetic susceptibility measurement indicates that, in the solid state, the radical remains paramagnetic and the fraction of Curie spins is 0.55 per molecule. Pressed pellet conductivity measurements indicate a value of σRT = 0.5 × 10−6 S/cm. The conductivity value is comparable with those of similarly packed phenalenyl based neutral radicals. Copyright © 2012 John Wiley & Sons, Ltd.
Co-reporter:Xiaojuan Tian, Santanu Sarkar, Matthew L. Moser, Feihu Wang, Aron Pekker, Elena Bekyarova, Mikhail E. Itkis, Robert C. Haddon
Materials Letters 2012 80() pp: 171-174
Publication Date(Web):
DOI:10.1016/j.matlet.2012.04.086
Co-reporter:Santanu Sarkar;Dr. Elena Bekyarova ; Robert C. Haddon
Angewandte Chemie 2012 Volume 124( Issue 20) pp:4985-4988
Publication Date(Web):
DOI:10.1002/ange.201201320
Co-reporter: Robert C. Haddon
ChemPhysChem 2012 Volume 13( Issue 16) pp:3581-3583
Publication Date(Web):
DOI:10.1002/cphc.201200555
Co-reporter:Santanu Sarkar;Dr. Elena Bekyarova ; Robert C. Haddon
Angewandte Chemie International Edition 2012 Volume 51( Issue 20) pp:4901-4904
Publication Date(Web):
DOI:10.1002/anie.201201320
Co-reporter:Hang Zhang, Elena Bekyarova, Jhao-Wun Huang, Zeng Zhao, Wenzhong Bao, Fenglin Wang, Robert C. Haddon, and Chun Ning Lau
Nano Letters 2011 Volume 11(Issue 10) pp:4047-4051
Publication Date(Web):August 29, 2011
DOI:10.1021/nl200803q
Chemical functionalization is a promising route to band gap engineering of graphene. We chemically grafted nitrophenyl groups onto exfoliated single-layer graphene sheets in the form of substrate-supported or free-standing films. Our transport measurements demonstrate that nonsuspended functionalized graphene behaves as a granular metal, with variable range hopping transport and a mobility gap ∼0.1 eV at low temperature. For suspended graphene that allows functionalization on both surfaces, we demonstrate tuning of its electronic properties from a granular metal to a semiconductor in which transport occurs via thermal activation over a transport gap ∼80 meV from 4 to 300 K. This noninvasive and scalable functionalization technique paves the way for CMOS-compatible band gap engineering of graphene electronic devices.
Co-reporter:Santanu Sarkar ; Elena Bekyarova ; Sandip Niyogi ;Robert C Haddon
Journal of the American Chemical Society 2011 Volume 133(Issue 10) pp:3324-3327
Publication Date(Web):February 22, 2011
DOI:10.1021/ja200118b
The zero-band-gap electronic structure of graphene enables it to function as either the diene or the dienophile in the Diels−Alder reaction, and this versatile synthetic method offers a powerful strategy for the reversible modification of the electronic properties of graphene under very mild conditions.
Co-reporter:Takashi Kubo ; Yoshiki Katada ; Akihiro Shimizu ; Yasukazu Hirao ; Kazunobu Sato ; Takeji Takui ; Mikio Uruichi ; Kyuya Yakushi ;Robert C. Haddon
Journal of the American Chemical Society 2011 Volume 133(Issue 36) pp:14240-14243
Publication Date(Web):August 11, 2011
DOI:10.1021/ja2065768
We have prepared and isolated neutral polycyclic hydrocarbon radicals. A butyl-substituted radical gave single crystals, in which a π-dimeric structure, not a σ-bonded dimer, was observed, even though steric protection was absent. Thermodynamic stabilization due to the highly spin-delocalized structure contributes effectively to the suppression of σ-bond formation.
Co-reporter:Santanu Sarkar, Sandip Niyogi, Elena Bekyarova and Robert C. Haddon
Chemical Science 2011 vol. 2(Issue 7) pp:1326-1333
Publication Date(Web):04 May 2011
DOI:10.1039/C0SC00634C
We explore the organometallic chemistry of graphitic materials and demonstrate the η6-complexation reactions of chromium with graphene, graphite and carbon nanotubes. All of these extended periodic π-electron systems exhibit some degree of reactivity toward the reagents Cr(CO)6 and (η6-benzene)Cr(CO)3, and we are able to demonstrate the formation of (η6-arene)Cr(CO)3 or (η6-arene)2Cr, where arene = single-walled carbon nanotubes (SWNT), exfoliated graphene (XG), epitaxial graphene (EG) and highly-oriented pyrolytic graphite (HOPG). We report the ATR-IR, Raman spectroscopy, XPS and chemistry of these new organometallic species and we observe clearly understandable trends in the chemistry and stability of the complexes based on curvature and surface presentation. For example, the SWNTs are the least reactive presumably as a result of the effect of curvature on the formation of the hexahapto bond; in the case of HOPG, (η6-HOPG)Cr(CO)3 was isolated while the exfoliated graphene samples were found to give both (η6-graphene)2Cr, and (η6-graphene)Cr(CO)3 structures. We report simple and efficient routes for the mild decomplexation of the graphene–chromium complexes which appears to restore the original pristine graphene state; exposure of the samples to white light in a solution of acetonitrile or the use of selected ligand competition reactions bring about a clean reversal of the metal complexation reactions and provide an independent proof of structure for the reaction products. This study represents the first example of the use of graphene as a ligand and is expected to expand the scope of graphene chemistry in connection with the application of this material in organometallic catalysis, where graphene can act as an electronically conjugated catalyst support.
Co-reporter:Irina Kalinina, Kimberly Worsley, Christopher Lugo, Swadhin Mandal, Elena Bekyarova, and Robert C. Haddon
Chemistry of Materials 2011 Volume 23(Issue 5) pp:1246
Publication Date(Web):January 27, 2011
DOI:10.1021/cm103030s
The carbon nanotube−polyethylene glycol (PEG) graft copolymer was synthesized by covalent functionalization of electric arc single-walled carbon nanotubes (SWNTs) with the monofunctional, tetrahydrofurfuryl-terminated polyethylene glycol PEG-THFF (MW∼200), to give a material composed of 80 wt % SWNTs. We show that the sequential processing of the resulting material by ultrasonication and high-shear mixing provides a means to disperse the SWNT-PEG-THFF macromolecules on two different length scales and leads to highly viscous solutions; at a concentration of 10 mg/mL the kinematic viscosity (ν) of an aqueous SWNT-PEG-THFF dispersion reaches a value of ν > 1000 cSt (for water ν ∼ 1 cSt). Analysis of this procedure by means of viscosity measurements and atomic force microscopy (AFM), shows that ultrasonication is effective in disrupting the SWNT bundles, while the high shear mixing disperses the individual SWNTs. The kinematic viscosity of aqueous dispersions of SWNT-PEG-THFF was measured as a function of nanotube concentration and compared to that of SWNT-PEG dispersions. The viscosity and AFM measurements show that the SWNT-PEG-THFF and SWNT-PEG graft copolymers form aqueous dispersions with distinct viscous characteristics; the use of monofunctional PEG-THFF for covalent functionalization of the SWNTs prevents cross-linking of the SWNTs in the final product, and this allows the production of more completely dispersed SWNTs than in the case of the SWNT-PEG graft copolymer, which is synthesized from a bifunctional glycol.Keywords (keywords): covalent functionalization; dispersion; kinematic viscosity; polyethylene glycol; single-walled carbon nanotubes;
Co-reporter:Arindam Sarkar, Fook S. Tham and Robert C. Haddon
Journal of Materials Chemistry A 2011 vol. 21(Issue 5) pp:1574-1581
Publication Date(Web):11 Oct 2010
DOI:10.1039/C0JM02397C
We report the synthesis, crystallization, electrochemistry, X-ray structure and electron density distribution of a methoxy-substituted-tris-phenalenyl based neutral radical (18); the cyclic voltammogram of the compound shows that the strategy of oxygen substitution at 3,7-positions and the utilization of tris-phenalenyls within the silicon complex reduce the electrochemical disproportionation potentials. The crystal structure shows that the radical exists as a 1D π-chain of partially superimposed phenalenyl rings with intermolecular carbon⋯carbon contacts that fall within van der Waals atomic separation. A bond length–bond order regression analysis of the experimental structures shows that the electron density is distributed over two out of the three phenalenyl units.
Co-reporter:Dr. Arindam Sarkar;Dr. Mikhail E. Itkis;Dr. Fook S. Tham ; Robert C. Haddon
Chemistry - A European Journal 2011 Volume 17( Issue 41) pp:11576-11584
Publication Date(Web):
DOI:10.1002/chem.201100730
Abstract
We report the synthesis, crystallization, and solid-state characterization of the 3,7-ethoxy-substituted spirobiphenalenyl-boron neutral radical 22. The radical is distinguished by its low disproportionation energy and one-dimensional structure. We show that our strategy of substitution of OEt group at the active positions of the phenalenyl units changes the crystal packing from its previously known OMe analogue and the solid-state properties are dictated by the partial π-stack structure and the oxygen atoms at the 3,7-positions and can be best rationalized in terms of the resonating valence bond model. Magnetic susceptibility measurements show that in the solid state the radical remains paramagnetic but there is significant spin–spin interaction between the molecules. Band structure calculations reflect efficient overlap between the molecules along the π stack and show evidence of interactions between the spin-bearing oxygen atoms. The room temperature electrical conductivity (σRT=2.0×10−2 S cm−1) of 22 is higher than that observed in previously known one-dimensional phenalenyl radicals.
Co-reporter:Sandip Niyogi, Elena Bekyarova, Jeongmin Hong, Sakhrat Khizroev, Claire Berger, Walt de Heer, and Robert C. Haddon
The Journal of Physical Chemistry Letters 2011 Volume 2(Issue 19) pp:2487-2498
Publication Date(Web):September 6, 2011
DOI:10.1021/jz200426d
The atomically flat surface of graphene provides an opportunity to apply carbon–carbon bond-forming chemical reactions to engineer the electronic properties of graphene circuitry. In particular, covalent functionalization of the surface or the edge of graphene ribbons provides a novel way to introduce patterning that can modulate the energy band gap, affect electron scattering, and direct current flow by producing dielectric regions in a graphene wafer. We discuss the use of Raman spectroscopy and scanning tunneling microscopy to characterize the surface functionalization periodicities and densities that have been produced by the chemical derivatization of epitaxial graphene together with the concomitant changes in the electronic and magnetic properties of the graphene surface layer.
Co-reporter:Elena Bekyarova;Irina Kalinina;Xiaobo Sun;Tejas Shastry;Kimberly Worsley;Xiaoliu Chi;Mikhail E. Itkis;Robert C. Haddon
Advanced Materials 2010 Volume 22( Issue 7) pp:848-852
Publication Date(Web):
DOI:10.1002/adma.200903427
Co-reporter:Feihu Wang, Mikhail E. Itkis and Robert C. Haddon
Nano Letters 2010 Volume 10(Issue 3) pp:937-942
Publication Date(Web):February 1, 2010
DOI:10.1021/nl9038423
We report a comprehensive study of the gate-induced electromodulated transmittance of infrared light by single-walled carbon nanotube (SWNT) thin films. The observed electromodulation is significantly enhanced by utilizing large diameter SWNTs, increasing the ratio of semiconducting to metal SWNTs, and by decreasing the SWNT film thickness. The amplitude of the effect reported herein (∼7%) is more than an order of magnitude larger than in previous SWNT thin film solid state devices.
Co-reporter:Sandip Niyogi, Elena Bekyarova, Mikhail E. Itkis, Hang Zhang, Kristin Shepperd, Jeremy Hicks, Michael Sprinkle, Claire Berger, Chun Ning Lau, Walt A. deHeer, Edward H. Conrad, and Robert C. Haddon
Nano Letters 2010 Volume 10(Issue 10) pp:4061-4066
Publication Date(Web):August 25, 2010
DOI:10.1021/nl1021128
In order to engineer a band gap into graphene, covalent bond-forming reactions can be used to change the hybridization of the graphitic atoms from sp2 to sp3, thereby modifying the conjugation length of the delocalized carbon lattice; similar side-wall chemistry has been shown to introduce a band gap into metallic single-walled carbon nanotubes. Here we demonstrate that the application of such covalent bond-forming chemistry modifies the periodicity of the graphene network thereby introducing a band gap (∼0.4 eV), which is observable in the angle-resolved photoelectron spectroscopy of aryl-functionalized graphene. We further show that the chemically-induced changes can be detected by Raman spectroscopy; the in-plane vibrations of the conjugated π-bonds exhibit characteristic Raman spectra and we find that the changes in D, G, and 2D-bands as a result of chemical functionalization of the graphene basal plane are quite distinct from that due to localized, physical defects in sp2-conjugated carbon.
Co-reporter:Palanisamy Ramesh ; Mikhail E. Itkis ; Elena Bekyarova ; Feihu Wang ; Sandip Niyogi ; Xiaoliu Chi ; Claire Berger ; Walt de Heer ;Robert C. Haddon
Journal of the American Chemical Society 2010 Volume 132(Issue 41) pp:14429-14436
Publication Date(Web):September 28, 2010
DOI:10.1021/ja101706j
We report the effect of electrochemical oxidation in nitric acid on the electronic properties of epitaxial graphene (EG) grown on silicon carbide substrates; we demonstrate the availability of an additional reaction channel in EG, which is not present in graphite but which facilitates the introduction of the reaction medium into the graphene galleries during electro-oxidation. The device performance of the chemically processed graphene was studied by patterning the EG wafers with two geometrically identical macroscopic channels; the electro-oxidized channel showed a logarithmic increase of resistance with decreasing temperature, which is ascribed to the scattering of charge carriers in a two-dimensional electronic gas, rather than the presence of an energy gap at the Fermi level. Field-effect transistors were fabricated on the electro-oxidized and pristine graphene channels using single-walled carbon nanotube thin film top gate electrodes, thereby allowing the study of the effect of oxidative chemistry on the transistor performance of EG. The electro-oxidized channel showed higher values for the on−off ratio and the mobility of the graphene field-effect transistor, which we ascribe to the availability of high-quality internal graphene layers after electro-oxidation of the more defective top layers. Thus, the present oxidative process provides a clear contrast with previously demonstrated covalent chemistry in which sp3 hybridized carbon atoms are introduced into the graphitic transport layer of the lattice by carbon−carbon bond formation, thereby opening an energy gap.
Co-reporter:Pradip Bag ; Mikhail E. Itkis ; Sushanta K. Pal ; Bruno Donnadieu ; Fook S. Tham ; Hyunsoo Park ; John A. Schlueter ; Theo Siegrist ;Robert C. Haddon
Journal of the American Chemical Society 2010 Volume 132(Issue 8) pp:2684-2694
Publication Date(Web):February 5, 2010
DOI:10.1021/ja908768a
We report the preparation of the first benzannulated phenalenyl neutral radical conductor (18), and we show that the compound displays unprecedented solid state behavior: the structure is dominated by two sets of intermolecular interactions: (1) a π-chain structure with superimposed π-overlap of the benzannulated phenalenyls along [0 0 1], and (2) an interchain overlap involving a pair of carbon atoms (C4) along [0 1 0]. The π-chain-type stacking motif is reminiscent of previously reported phenalenyl radicals and the room temperature structure (space group P2/c) together with the conductivity of σRT = 0.03 S/cm and the Pauli-like magnetic susceptibility are best described by the resonating valence bond (RVB) model. The interchain interaction is unstable with respect to the formation of a σ-charge density wave (σ-CDW) involving pairs of C4 carbon atoms between adjacent radicals and this phase is characterized by the P21/c space group which involves a doubling of the unit cell along the [0 1 0] direction. The RVB and CDW phases compete for structural occupancy throughout the whole temperature range (15−293 K) with the RVB phase predominating at 15 and 293 K and the σ-CDW phase achieving a maximum structural occupancy of about 60% at 150 K where it produces clearly discernible effects on the magnetism and conductivity.
Co-reporter:Sushanta K. Pal ; Pradip Bag ; Arindam Sarkar ; Xiaoliu Chi ; Mikhail E. Itkis ; Fook S. Tham ; Bruno Donnadieu ;Robert C. Haddon
Journal of the American Chemical Society 2010 Volume 132(Issue 48) pp:17258-17264
Publication Date(Web):November 16, 2010
DOI:10.1021/ja107201d
We have investigated the solid-state electronic structure and properties of a phenalenyl-based butyl-substituted neutral radical, 3, that shows a hysteretic phase transition just above room temperature. We quantitatively analyzed the electron density distribution of this radical throughout both branches of the hysteretic phase transition using solid-state X-ray structures and found two distinct electronic states in the hysteresis loop that accompanies the phase transition. The bistability of the two electronic states was observed through a number of measurements, including IR transmittance spectra of single crystals in the vicinity of the phase transition. By comparing the changes in the crystal structures of 3 and the related ethyl-substituted radical 1 (which exhibits no hysteresis) at various temperatures, we show that the change in the interplanar π−π distance within dimers is the most important structural parameter in determining the physical properties of the radicals. The large change in the C−H···π interaction in 3 occurs in concert with the spin redistribution during the phase transition, but these factors are not responsible for the hysteresis effect. We suggest that the presence of a high-temperature state inside the hysteretic loop during the cooling cycle is due to thermodynamic stability, while the existence of the low-temperature state during the heating cycle is due to the presence of a large energy barrier between the two states (estimated to be greater than 100 kJ/mol) that results from the large-amplitude motion of the phenalenyl rings and the associated lattice reorganization energy that is required at the phase transition.
Co-reporter:Arindam Sarkar, Sushanta K. Pal, Mikhail E. Itkis, Puhong Liao, Fook S. Tham, Bruno Donnadieu and Robert C. Haddon
Chemistry of Materials 2009 Volume 21(Issue 11) pp:2226
Publication Date(Web):May 4, 2009
DOI:10.1021/cm900242a
We report the synthesis, crystallization, and solid-state characterization of spiro-bis(3,7-dimethoxy-1,9-dioxophenalenyl) boron neutral radical 17; the radical is distinguished by its oxygen functionalization and we show that our strategy of oxygen substitution at the active positions of the phenalenyl units reduces the electrochemical disproportionation potential. The crystal structure shows that the radical exists as a π-dimer at room temperature and a one-dimensional (1D) π-chain of alternating superimposed and partially superimposed phenalenyl units at 100 K. Magnetic susceptibility measurements show that in the solid state, the radical remains paramagnetic but there is significant spin−spin interaction between the molecules along the π-chains. Band structure calculations delineate the response of the electronic structure to the structural changes observed in the crystal lattice, although magnetic and conductivity measurements do not show any sign of a phase transition. The room temperature electrical conductivity (σRT = 3.0 × 10−3 S/cm) apparently results from the discontinuous character of the π-chains formed by the alternating superimposed and nonsuperimposed phenalenyl units.
Co-reporter:Aiping Yu;Palanisamy Ramesh;Xiaobo Sun;Elena Bekyarova;Mikhail E. Itkis ;Robert C Haddon
Advanced Materials 2008 Volume 20( Issue 24) pp:4740-4744
Publication Date(Web):
DOI:10.1002/adma.200800401
Co-reporter:Mikhail E. Itkis, Aiping Yu and Robert C. Haddon
Nano Letters 2008 Volume 8(Issue 8) pp:2224-2228
Publication Date(Web):July 4, 2008
DOI:10.1021/nl080814u
We use the suspended single-walled carbon nanotube (SWNT) thin film technology to assemble the first prototype of an integrated optoelectronic SWNT device, a SWNT optocoupler in which a SWNT emitter and a SWNT detector couple two electrical circuits by the transmission of a signal through the optical channel. Our experiments show that the integrated SWNT emitter/SWNT detector is an ideal couple in which the broadband wavelength character of the emission matches the broadband detection capabilities.
Co-reporter:Palanisamy Ramesh ; Mikhail E. Itkis ; Jason M. Tang ;Robert C. Haddon
The Journal of Physical Chemistry C 2008 Volume 112(Issue 24) pp:9089-9094
Publication Date(Web):May 28, 2008
DOI:10.1021/jp711280j
A thin film of single-wall carbon nanotubes (SWNTs) and SWNT−multiwall carbon nanotube (MWNT) hybrids loaded with Pt have been evaluated as the cathode catalyst layer in proton exchange membrane fuel cells. The optimum Pt loading and thickness for SWNT films is found to be in the range of 20−100 µg Pt/cm2 and 0.3−1.4 µm, respectively. In this optimum range, Pt-SWNT thin films show excellent proton conductivity and are able to reach peak performance without additional nafion in the catalyst layer. Cathode-specific mass activity of Pt on a SWNT support is found to decrease as the Pt loading and thickness increase due to mass transfer limitations. Addition of Pt-MWNTs to Pt-SWNT thin films is found to increase the mass transport characteristics and cathode-specific mass activity. A SWNT−MWNT hybrid support shows three times higher mass activity than a SWNT support at about the same power output, and the optimum hybrid is found for a blend composed of 20−30 µgPt/cm2 on SWNTs and 5−10 µgPt/cm2 on MWNTs.
Co-reporter:Mikhail E. Itkis;Ferenc Borondics;Aiping Yu;Robert C. Haddon
Science 2006 Vol 312(5772) pp:413-416
Publication Date(Web):21 Apr 2006
DOI:10.1126/science.1125695
Abstract
The photoresponse in the electrical conductivity of a single-walled carbon nanotube (SWNT) film is dramatically enhanced when the nanotube film is suspended in vacuum. We show here that the change in conductivity is bolometric (caused by heating of the SWNT network). Electron-phonon interactions lead to ultrafast relaxation of the photoexcited carriers, and the energy of the incident infrared (IR) radiation is efficiently transferred to the crystal lattice. It is not the presence of photoexcited holes and electrons, but a rise in temperature, that results in a change in resistance; thus, photoconductivity experiments cannot be used to support the band picture over the exciton model of excited states in carbon nanotubes. The photoresponse of suspended SWNT films is sufficiently high that they may function as the sensitive element of an IR bolometric detector.
Co-reporter:Aiping Yu, Hui Hu, Elena Bekyarova, Mikhail E. Itkis, Junbo Gao, Bin Zhao, Robert C. Haddon
Composites Science and Technology 2006 Volume 66(Issue 9) pp:1190-1197
Publication Date(Web):July 2006
DOI:10.1016/j.compscitech.2005.10.023
Single-walled carbon nanotubes (SWNTs) were dispersed in the form of individual nanotubes and small bundles, and subsequently polymerized to prepare composite films. The nanotubes were first dispersed in dimethylacetamide in the presence of 1,3-bis(3-aminophenoxy)benzene (APB), which was then polymerized with 4,4′-hexafluoroisopropylidiene diphthalic anhydride (6-FDA). Optical microscopy, SEM and TEM studies of the composite show that the SWNTs are homogenously distributed in the polymer matrix, and AFM observations indicate that ∼80% of the dispersed SWNTs are stabilized as individual nanotubes. The freestanding composite films were found to have very good optical, thermal and mechanical properties as well as enhanced electrostatic charge dissipation properties.
Co-reporter:S. K. Pal;M. E. Itkis;F. S. Tham;R. W. Reed;R. T. Oakley;R. C. Haddon
Science 2005 Vol 309(5732) pp:281-284
Publication Date(Web):08 Jul 2005
DOI:10.1126/science.1112446
Abstract
An organic material composed of neutral free radicals based on the spirobiphenalenyl system exhibits a room temperature conductivity of 0.3 siemens per centimeter and a high-symmetry crystal structure. It displays the temperature-independent Pauli paramagnetism characteristic of a metal with a magnetic susceptibility that implies a density of states at the Fermi level of 15.5 states per electron volt per mole. Extended Hückel calculations indicate that the solid is a three-dimensional organic metal with a band width of ∼0.5 electron volts. However, the compound shows activated conductivity (activation energy, 0.054 electron volts) and an optical energy gap of 0.34 electron volts. We argue that these apparently contradictory properties are best resolved in terms of the resonating valence-bond ground state originally suggested by Pauling, but with the modifications introduced by Anderson.
Co-reporter:B. Zhao;H. Hu;R. C. Haddon
Advanced Functional Materials 2004 Volume 14(Issue 1) pp:
Publication Date(Web):29 JAN 2004
DOI:10.1002/adfm.200304440
Poly(m-aminobenzene sulfonic acid) (PABS), was covalently bonded to single-walled carbon nanotubes (SWNTs) to form a water-soluble nanotube–polymer compound (SWNT–PABS). The conductivity of the SWNT–PABS graft copolymer was about 5.6 × 10–3 S cm–1, which is much higher than that of neat PABS (5.4 × 10–7 S cm–1). The mid-IR spectrum confirmed the formation of an amide bond between the SWNTs and PABS. The 1H NMR spectrum of SWNT–PABS showed the absence of free PABS, while the UV/VIS/NIR spectrum of SWNT–PABS showed the presence of the interband transitions of the semiconducting SWNTs and an absorption at 17 750 cm–1 due to the PABS addend.
Co-reporter:Sandip Niyogi;Robert C. Haddon
PNAS 2004 101 (17 ) pp:6331-6332
Publication Date(Web):2004-04-27
DOI:10.1073/pnas.0401508101
Co-reporter:K. Kamaras;M. E. Itkis;H. Hu;B. Zhao;R. C. Haddon
Science 2003 Vol 301(5639) pp:1501
Publication Date(Web):12 Sep 2003
DOI:10.1126/science.1088083
Metallic single-walled carbon nanotubes can be changed into semiconductors by reacting them with dichloromethane.
Co-reporter:Matthew L. Moser, Xiaojuan Tian, Aron Pekker, Santanu Sarkar, Elena Bekyarova, Mikhail E. Itkis and Robert C. Haddon
Dalton Transactions 2014 - vol. 43(Issue 20) pp:NaN7382-7382
Publication Date(Web):2014/02/20
DOI:10.1039/C3DT53291G
We report the response of the electrical conductivity of semiconducting single-walled carbon nanotube (SWNT) thin films on exposure to metal vapors of the early lanthanides under high vacuum conditions. We attribute the strongly enhanced conductivities observed on deposition of samarium and europium to charge transfer from the metals to the SWNT backbone, thereby leading to the first examples of mixed covalent–ionic bis-hexahapto bonds [(η6-SWNT)M(η6-SWNT), where M = Sm, Eu].
Co-reporter:Arindam Sarkar, Fook S. Tham and Robert C. Haddon
Journal of Materials Chemistry A 2011 - vol. 21(Issue 5) pp:NaN1581-1581
Publication Date(Web):2010/10/11
DOI:10.1039/C0JM02397C
We report the synthesis, crystallization, electrochemistry, X-ray structure and electron density distribution of a methoxy-substituted-tris-phenalenyl based neutral radical (18); the cyclic voltammogram of the compound shows that the strategy of oxygen substitution at 3,7-positions and the utilization of tris-phenalenyls within the silicon complex reduce the electrochemical disproportionation potentials. The crystal structure shows that the radical exists as a 1D π-chain of partially superimposed phenalenyl rings with intermolecular carbon⋯carbon contacts that fall within van der Waals atomic separation. A bond length–bond order regression analysis of the experimental structures shows that the electron density is distributed over two out of the three phenalenyl units.
Co-reporter:Arindam Sarkar, Sushanta K. Pal, Mikhail E. Itkis, Fook S. Tham and Robert C. Haddon
Journal of Materials Chemistry A 2012 - vol. 22(Issue 17) pp:NaN8256-8256
Publication Date(Web):2012/03/16
DOI:10.1039/C2JM16001C
We report a synthetic scheme for the preparation of alkylthio, dithio-bridged and diseleno-bridged 9-hydroxyphenalenones and associated spiro-biphenalenyl boron neutral radicals. We show that the strategy of sulfur substitution at the active positions of the phenalenyl units reduces the electrochemical disproportionation potential (ΔE2−1 = E2½ − E1½, where E1½ and E2½ are the first and second reduction potentials of corresponding cations) of the alkylthio-radicals [3,7-SR-PLY(O,O)]2B, (R = Me, 9), (R = Et, 10) and (R = Pr, 11), but brings about a significant reduction of the ΔE2−1 value in the case of disulfide and diselenide substitution, [3,4-S,S-PLY(O,O)]2B (12) and [3,4-Se,Se-PLY(O,O)]2B (13). The crystal structures of 10 and 11 show that the radicals exist as one dimensional (1-D) π-chains of superimposed phenalenyl units, and the molecular units pack more efficiently than the oxygen-substituted analog [3,7-OMe-PLY(O,O)]2B (8). Magnetic susceptibility measurements indicate that in the solid state the radicals remain paramagnetic while there is spin–spin interaction between the molecules along the π-chains. Band structure calculations are in accordance with the magnetic measurement data and indicate the presence of interactions between the molecules. The room temperature electrical conductivities of both compounds are found to be σRT = 1.5 × 10−2 S cm−1.
Co-reporter:Santanu Sarkar, Sandip Niyogi, Elena Bekyarova and Robert C. Haddon
Chemical Science (2010-Present) 2011 - vol. 2(Issue 7) pp:NaN1333-1333
Publication Date(Web):2011/05/04
DOI:10.1039/C0SC00634C
We explore the organometallic chemistry of graphitic materials and demonstrate the η6-complexation reactions of chromium with graphene, graphite and carbon nanotubes. All of these extended periodic π-electron systems exhibit some degree of reactivity toward the reagents Cr(CO)6 and (η6-benzene)Cr(CO)3, and we are able to demonstrate the formation of (η6-arene)Cr(CO)3 or (η6-arene)2Cr, where arene = single-walled carbon nanotubes (SWNT), exfoliated graphene (XG), epitaxial graphene (EG) and highly-oriented pyrolytic graphite (HOPG). We report the ATR-IR, Raman spectroscopy, XPS and chemistry of these new organometallic species and we observe clearly understandable trends in the chemistry and stability of the complexes based on curvature and surface presentation. For example, the SWNTs are the least reactive presumably as a result of the effect of curvature on the formation of the hexahapto bond; in the case of HOPG, (η6-HOPG)Cr(CO)3 was isolated while the exfoliated graphene samples were found to give both (η6-graphene)2Cr, and (η6-graphene)Cr(CO)3 structures. We report simple and efficient routes for the mild decomplexation of the graphene–chromium complexes which appears to restore the original pristine graphene state; exposure of the samples to white light in a solution of acetonitrile or the use of selected ligand competition reactions bring about a clean reversal of the metal complexation reactions and provide an independent proof of structure for the reaction products. This study represents the first example of the use of graphene as a ligand and is expected to expand the scope of graphene chemistry in connection with the application of this material in organometallic catalysis, where graphene can act as an electronically conjugated catalyst support.
