17872
J. Phys. Chem. C 2007, 111, 17872-17878
Characterizing Covalently Sidewall-Functionalized SWNTs† Donna J. Nelson,* Heather Rhoads, and Christopher Brammer Department of Chemistry and Biochemistry, UniVersity of Oklahoma, Norman, Oklahoma 73019 ReceiVed: February 16, 2007; In Final Form: June 12, 2007
Pristine single-walled carbon nanotubes (p-SWNTs) were converted to 4-chlorophenyl-SWNTs 1 via treatment with 4-chlorophenylamine and isoamylnitrite, and subsequently to 4-mercaptophenyl-SWNTs 2 by using sodium ethanethiolate. Products 1 and 2 were characterized by Raman, UV/vis/NIR, TGA, IR, and 1H NMR. We report a COSY 1H NMR of 1, which appears to be the first such spectrum reported for a covalently sidewallfunctionalized SWNT.
Introduction Since the discovery of carbon nanotubes,1,2 there has been an intense effort to characterize and understand their properties and structural details in order to enable their medical, electronic, and mechanical applications, which will improve all aspects of life. Although Raman, UV/vis/NIR, thermogravimetric analysis (TGA), and IR have been employed to characterize carbon nanotubes for years, only recently has NMR been used to study the growth, functionalization, and electric and magnetic response of multiwalled wall carbon nanotubes (MWNTs),3-5 and even less so single-walled carbon nanotubes (SWNTs). Since then, theoretical calculations have predicted the (n,m) values of armchair and zigzag SWNTs, as well as how semiconducting and metallic SWNTs can be differentiated by 13C NMR.6-9 With this background, NMR of SWNTs has been generally used to (1) confirm structural properties, electronic properties, phase transitions, and dynamics of SWNTs,10 (2) determine the difference between and potential separation of metallic versus semiconducting SWNTs,11 (3) study the effects of cutting, bending, and twisting SWNT upon their electronic properties, and (4) locate defects in the SWNT structure.12,13 NMR has also been a useful guide for optimizing synthesis of SWNTs intended for specific applications: (1) In situ NMR increased understanding of SWNT synthesis under varying reaction conditions and confirmed its mechanism.14-16 (2) SWNT end opening and closing can be monitored via in situ NMR, providing a guideline for potential energy-storage applications.17 (3) NMR probed SWNT ability to store hydrogen gas, methane gas, or water at various concentrations, temperatures, and pressures.18-22 (4) NMR was used in order to distinguish adsorption sites, the adsorption mechanism, the strength of adsorption, and the location of the molecules inside the SWNTs.23-26 (5) Lithium- and cesium-intercalated SWNTs were studied by using NMR to discover storage location, storage capacity, and metallic and electronic property changes.27-32 (6) NMR probed SWNT-polymer matrix structures, which provided storage for hexogen (hexahydro-1,3,5-trinitro-1,3,5-triazin) or improved polymer physical properties.33-41 NMR has been used to characterize two types of sidewall SWNT functionalization, noncovalently and covalently bonded. Noncovalent functionalization using reactants such as pyrene †
Part of the special issue “Richard E. Smalley Memorial Issue”. * Corresponding author. E-mail:
[email protected].
carrying ammonium ion or THPP, have been explored via NMR in order to determine both functionalization type and mechanism.42,43 We found few NMR studies of SWNTs with covalent end functionalization,44,45 but many of SWNTs with covalentlybonded sidewall functionalities. NMR has been especially useful in studying SWNTs with substituents covalently bonded to their sidewalls: (1) Radical reactions constitute one type of reaction, which provides SWNT sidewall functionalization and gives products with important applications, such as SWNT/polymer composites; these new materials and their mechanisms of formation have been studied by 1H, 13C, 11B, 19F, and 29Si NMR.46-49 (2) Reversible protonation has been studied via NMR in order to determine SWNT functionalization and structure.50 (3) NMR was used to characterize Diels-Alder SWNT functionalization with oquinodimethane and fluorine.51,52 (4) Cycloaddition of nitrenes and of carbenes to SWNTs has been confirmed by NMR spectroscopy.46,53-55 (5) NMR confirmed 1,3-dipolar cycloaddition-mediated attachment of nitrile imines or nitrile oxides to SWNT sidewalls, creating new photochemically active materials.56,57 However, few46,47,52-54,56,57 of the above were proton NMR studies of SWNTs in solution, although proton NMR should be extremely valuable for determining the identity and regiochemistry of organic functional groups attached to SWNTs. Consequently, it was desirable to characterize by NMR the products of another solution-phase SWNT functionalization reaction,58,59 which we found to be extremely useful and interesting. Results An ingenious solvent-free method of SWNT sidewall functionalization58 initially seemed promising because it should avoid both the typically difficult solvent removal from SWNTs and complications created by the solvent in some spectroscopic methods of analysis.58 Unfortunately, this solvent-free synthetic route gave a 21 wt % degree of functionalization,58 a “yield” that we feared might be too low for typical 1H NMR analysis. However, the authors also reported that by running the above reaction in the solvent ortho-dichlorobenzene (ODCB) the degree of functionalization increased to 49 wt %.59 We expected that the higher degree of functionalization in ODCB to give 1 would be sufficient to permit its characterization by NMR analysis, so we pursued its synthesis and further modification to 4-mercaptophenyl-SWNT 2 (Scheme 1).
10.1021/jp071326y CCC: $37.00 © 2007 American Chemical Society Published on Web 08/25/2007
Covalently Sidewall-Functionalized SWNTs
J. Phys. Chem. C, Vol. 111, No. 48, 2007 17873
SCHEME 1
Although we knew of problems inherent in NMR characterization of SWNT reaction products in solution (vide infra), we also knew that NMR could provide strong evidence to support product identification. Therefore, we pursued characterizing 1 and 2 by NMR in order to confirm the functional identity and explore possible NMR sensitivity to the degree of SWNT functionalization. Consequently, below we report our NMR analysis and spectra of covalently sidewall-functionalized SWNT products 1 and 2. A. Synthesis and Characterization of 4-ChlorophenylSWNT 1. We synthesized 1 via both of the above synthetic methods (with and without solvent) and characterized both products by a variety of techniques including Raman, UV/vis/ NIR, TGA, and IR; our results were analogous to previously reported Raman,58,59 UV/vis/NIR,58,59a,b,d and TGA58,59a,c,d spectra for 1. The Raman spectrum of 1 (Figure 1B) had both the radial breathing mode (100-400 cm-1) and an observed G-band (1585 cm-1); these were comparable to those of pristine-SWNTs (p-SWNTs)60 (Figure 1A). The Raman disorder band (1290 cm-1) increased greatly upon conversion to 1, in keeping with SWNT covalent sidewall functionalization.58,59 However, the Raman spectra of SWNTs reveal disruptions of the sp2 matrix with sp3-hybridized carbon, but not the causes of disruptions; any defect appears the same as a functionalization.61 Our p-SWNTs show typical58,59a,b,d van Hove’s singularities in the UV/vis/NIR spectra, which are lost upon conversion to 1 (Figure 2), as expected for any covalent sidewall functionalization.58,59a,b,d However, van Hove’s singularities are due to extended π conjugation in SWNTs and can be disrupted by SWNT defects as well as covalent functionalization;62 therefore, either of these conditions can cause complete loss of the singularities. Consequently, Raman and UV/vis/NIR will neither distinguish between defects and functionalization nor define the covalent sidewall functionality structure or regiochemistry. Therefore, these two spectroscopic methods gave no direct evidence that we had 1 in hand, but they did provide us spectra which matched those from the synthesis of 1 reported earlier.58,59 TGA can determine the degree of SWNT functionalization by sufficiently heating the material in an inert environment in order to remove the functional moiety leaving the p-SWNTs, and then measuring the mass loss. Our TGA (10 °C/min to 810 °C, Ar) of 1 synthesized in ODCB displayed a mass loss of 49.6% (Figure 3A); this agrees with the earlier report59d in regard to mass loss (49%) as well as inflection points. Both spectra show a major inflection point above 700 °C and a smaller one below 400 °C. The major difference seems to be an additional very-small (∼1% weight loss) inflection point in our spectrum at ∼200 °C, which probably corresponds to adsorbed gas evolution.
Figure 1. Raman spectra (633 nm): (A) p-SWNT displays a small D-band, which is increased greatly in the products, (B) 4-chlorophenylSWNT 1, and (C) 4-mercaptophenyl-SWNT 2.
Stronger evidence for the conversion of p-SWNTs to 1 was obtained from IR and NMR. Our IR spectrum of p-SWNTs displays a broad C-H stretch at 3400 cm-1 and an aromatic stretch at 1600 cm-1; conversion to 1 introduced a new C-Cl stretch at 1093 cm-1, which appears as a significantly enlarged band in that region, compared to that of the p-SWNT (Figure 4A and B). The IR of 1 is similar to those of other aryl-SWNTs functionalized in the para position.58,59 The difference in the C-Cl stretch frequencies for 1 versus the reactant p-chloroaniline (1095 cm-1)63b is ∆ν ) -2 cm-1, which is similar in magnitude to those calculated for aryl-SWNTs reported by Tour, et al.58 The IR for 1 also resembles those for model compounds Cl-Ph-R; IR frequencies for C-Cl stretches in Cl-Ph-R with R ) SWNT, Ph, Me, and H are 1093, 1100, 1083, and 1091 cm-1, respectively (Table 1).63 Hoping to identify an optimal model for SWNT, we also compared the characteristic frequen-
17874 J. Phys. Chem. C, Vol. 111, No. 48, 2007
Nelson et al.
Figure 2. UV/vis/NIR spectra of (A) p-SWNT displays van Hove singularities, but the products, (B) 4-chlorophenyl-SWNT 1 and (C) 4-mercaptophenyl-SWNT 2, lost the van Hove singularities upon functionalization.
Figure 3. TGA spectra indicate the degree of functionalization for (A) 4-chlorophenyl-SWNT 1 (49.6 wt % loss) and (B) 4-mercaptophenyl-SWNT 2 (82 wt % loss).
Figure 4. IR spectra of (A) p-SWNT as a KBr pellet, (B) 4-chlorophenyl-SWNT 1 as a KBr pellet, and (C) 4-mercaptophenyl-SWNT 2 in DMF. In spectrum B, new C-H stretches at 2920 and 2854 cm-1, correspond to the 4-chlorophenyl moiety of 1. In spectrum C, the band at 2505 cm-1 corresponds to the SH stretch of the expected mercapto product 2.
cies that Tour reported for his other functionalized SWNTs versus their model compounds (Table 1): 2954 cm-1 for t-BuPh-SWNT (CH stretch), 1722 cm-1 for MeOCO-Ph-SWNT (CdO stretch), and 1516 and 1339 cm-1 for NO2-Ph-SWNT (NO2). However, no model gave optimal agreement with the SWNT IR frequency consistently. We found that the above-mentioned solvent-free SWNT sidewall functionalization gave 1 with a degree of functionalization sufficiently low58 to preclude NMR analysis. However, the higher-yield SWNT sidewall functionalization in ODCB solvent59a,d gave an NMR signal suitable for analysis. Nevertheless, additional challenges arose when characterizing functionalized SWNTs by using NMR, such as (1) bulkiness of the carbon material and bundling of SWNT due to van der Waals
forces, (2) NMR signals from water or small amounts of impurities can swamp the SWNT product signal, (3) 1H NMR requires ∼8 mg/mL in order to obtain a spectrum in reasonable time, so low (0.25 mg/mL) SWNT solubility necessitated overnight runs in order to obtain 1000 acquisitions, (4) higher degrees of functionalization are needed in order to observe the functional group; in order to achieve this, reaction times longer than those reported previously58,59 with solvent were required. Even with precautions for these challenges, we found that because of the NMR sensitivity that our analysis required, remaining slight solvent impurities sometimes complicated the spectra. The NMR of 1 (Varian VNMRS 500 MHz Spectrometer) has two rather broad signals in the aromatic region at 8.12 and
Covalently Sidewall-Functionalized SWNTs
J. Phys. Chem. C, Vol. 111, No. 48, 2007 17875
TABLE 1: Select IR Data (cm-1) for Functionalized SWNTs and Their Models, p-R-Ph-Xa -X R-
SWNTPhHt-BuMea
-Cl (CCl)
-SH (SH)
-t-Bu (CH)
-CO2Me (CdO)
-NO2 (NO2)
1093
2511
2954b
1722b
1516, 1339b
2568 2557 2568
2962 2967 2956 2966
1724 1725 1724
1515, 1347 1521, 1347 1524, 1347 1512, 1346
1100 1083 1091
Data for models are from ref 63c. b Ref 58.
7.94 ppm (Figure 5A). The broadness could be due to long relaxation times, possibly resulting from the large SWNT size, or due to the aromatic functionalities associating with other SWNTs or other aromatic groups on the same or other SWNTs. To facilitate analysis and reveal aromatic spin-spin coupling, we obtained a 2D correlation spectroscopy (COSY) spectrum (Figure 6), which appears to be the first reported for a covalently functionalized SWNT; a previous report demonstrated a 2D COSY spectrum of SWNT with 5,7-eicosadiynylamine physisorbed on the surface, but not covalently bonded.39 The COSY spectrum of 1 (Figure 6) reveals that the two aromatic signals are coupled and 0.18 ppm apart. This shift difference is comparable to those of 4-chlorobiphenyl (signals at 7.49 and 7.38 ppm),63a of t-butyl-4-chlorobenzene (signals at 7.31 and 7.25 ppm),63d and of 4-chlorotoluene (signals at 7.14 and 7.01 ppm),63b (Table 2), which are 0.11, 0.06, and 0.13 ppm, respectively. Relative to the aromatic peaks in 4-chloroaniline (6.99 and 6.46 ppm64 or 7.04 and 6.54 ppm63b), aromatic peaks for 1 and its comparators above are farther downfield and closer together. We are currently exploring this spectrum and additional COSY spectra of covalently functionalized SWNTs further and will report a more-detailed analysis at a later date. With no previous report of covalently functionalized SWNT NMRs, we had no direct way to gauge whether the observed rather large downfield shift for aromatic protons in 1 was reasonable. Therefore, we compared this shift for 1 vs its models in Table 2, by using midpoints of multiplets and averages of multiple peaks; for these chloro-functionalized compounds, the downfield shifts obtained upon substituting SWNT for Ph, H, t-Bu, and Me were 0.61, 0.75, 0.76, and 0.96 ppm, respectively. The NMRs of 1 and its comparators are discussed in more detail and compared with those of 2 and its comparators below. B. Synthesis and Characterization of 4-MercaptophenylSWNT 2. To synthesize 2 from 4-chlorophenyl-SWNT 1, we adapted a procedure from a previous report66 for conversion of chlorobenzene to benzenethiol. Compound 1 reacted with sodium ethanethiolate, followed by mild acid workup, to give 2; this product is desirable for exploring possible development of SWNTs for sensor applications. The Raman spectrum of 2 (Figure 1C) was similar to that of 1 (Figure 1B) in that they both showed a greatly increased disorder band relative to that of p-SWNT (Figure 1A); this is consistent with conversion of the covalent sidewall functionality 4-chlorophenyl to 4-mercaptophenyl. UV/vis/NIR spectra of 2 show no van Hove’s singularities (Figure 2C). The major inflection point in the TGA spectrum of 2 was centered at ∼450 °C and indicated 82% weight loss (Figure 3B); this result supported functionalization, but it did not indicate the functionality identity. Thus, the above
Figure 5. 1H NMR spectra of (A) p-SWNT, (B) 4-chlorophenyl-SWNT 1, and (C) 4-mercaptophenyl-SWNT 2.
spectroscopic data fit, but do not evidence, that 1 has been converted to 2. As in characterizing 1, stronger evidence for the presence of 2 was obtained from IR and from NMR. Upon reacting 1 as described above, the C-Cl stretch in 1 disappeared and a new band at 2505 cm-1 (SH stretch) appeared (Figure 4C), which we compared versus SH stretches in model compounds HSPh-R (Table 1); IR data for the series R ) SWNT, H, t-Bu, and Me reveal SH stretches at 2505, 2568, 2557, and 2564 cm-1, respectively. Product 2 NMR (Figure 5B) displays a broad singlet in the aromatic region (8.11 ppm), as compared to the NMR data for models in Table 2, 4-mercaptobiphenyl (7.68-7.44 ppm), thiophenol (7.42 - 6.97 ppm), p-t-butylbenzenethiol (7.17 ppm) and 4-toluenethiol (7.16 and 7.14 ppm). Comparing the signal for aromatic protons in 2 versus those of suitable models, as
17876 J. Phys. Chem. C, Vol. 111, No. 48, 2007
Nelson et al.
Figure 6. COSY 1H NMR spectrum of 4-chlorophenyl-SWNT 1 displays coupling of aromatic peaks at 8.12 and 7.94 ppm.
TABLE 2: NMR Data (ppm) for Functionalized SWNTs and Their Models p-R-Ph-X -X R-
-Cl 8.12(s,br), 7.94(s,br)
-SH 8.11(s,br)
protons in 4-chlorophenyl-SWNT 1 and 4-mercaptophenylSWNT 2, versus those of model compounds p-Cl-Ph-R and p-HS-Ph-R, respectively, reveals that R ) Ph gives a better model than R ) H, t-Bu, or Me. However, comparing IR frequencies in the same series of compounds indicates that there is no model that is consistently the best. Experimental Section
SWNTPhHt-BuMea
7.38(d)a
7.49(d), ; 7.65-7.26(m)b 7.43-7.14(m)b 7.31(d), 7.25(d)d 7.14(m), 7.01(m)d
7.68-7.44(m)
c
7.42-6.97(m)b 7.17(m)e 7.16(m), 7.14(m)b; 7.05(m)e
Ref 63a. bRef 63b. cRef 63c. dRef 63. eRef 63e.
was done for the chlorophenyl compounds above, revealed that substituting SWNT for Ph, H, t-Bu, and Me produced downfield shifts of 0.55, 0.91, 0.94, and 0.96 ppm, respectively. These shifts are remarkably similar to those in the chloro system above, 0.61, 0.75, 0.76, and 0.96 ppm, respectively. Conclusions We have demonstrated that 2D correlation NMR spectroscopy (COSY) can be applied to characterize functionalities covalently attached to SWNT sidewalls via what seems to be the first such COSY spectrum reported. Comparing NMR shifts of aromatic
Synthetic Procedures. Purified powder SWNTs were donated from Southwest Nanotechnologies, Norman, OK. Isoamyl nitrite, o-dichlorobenzene, acetonitrile, EtSNa, and DMF were purchased from Aldrich and utilized without further treatment. Adapting procedures reported previously,58,59 SWNTs (1.5 mmol) were dispersed in 10 mL o-dichlorobenzene (ODCB) by horn sonication (20 min). SWNT/ODCB solution and 4-chloroanline (6 mmol) were dissolved in acetonitrile and added to a two-necked flask equipped with a reflux condenser and a magnetic stir bar. To achieve inert conditions, we sparged the system with nitrogen for 30 min. Then, the flask containing the solution was lowered into a preheated (60 °C) oil bath, and isoamyl nitrite (9 mmol) was injected into the flask via syringe. The reaction was stirred vigorously at 60 °C under nitrogen for 24 h with two additional injections of 4-chloroanline and isoamyl nitrite, once at 5 h and again at 10 h. Upon reaction completion, the solution was filtered utilizing a 0.2 µm PTFE membrane (Millipore) and washed with DMF until a color change was observed. Product purification was performed by repeating DMF sonication and washing. DMF was removed with an ether wash,
Covalently Sidewall-Functionalized SWNTs and then the product was vacuum-dried at 65 °C overnight. The product was analyzed for 4-chlorophenyl functionalities on the SWNT sidewalls. 4-Chlorophenyl-SWNTs (0.5 mmol) were dispersed in 10 mL DMF with horn sonication (30 min) and then added to a twonecked flask equipped with a magnetic stir bar and a reflux condenser. To achieve inert conditions, we sparged the solution with nitrogen for 30 min prior to the addition of EtSNa. Upon addition of 7.5 mmol EtSNa, the solution was refluxed with continuous stirring for 3 days. The solution was filtered and washed initially with 10 mL of 1.0 M HCl (1:1 by volume), and then with 80 mL ethanol. NMR Spectra Acquisition. Samples of p-SWNT, 1, and 2 were each prepared by horn sonicating (30 min) a small amount (∼0.5 mg) in 10 mL of d6-DMSO; the resulting solution was added by pipet into a 5-mm NMR tube (Wilmad, 503-PS). NMR measurements were acquired on a Varian VNMRS 500 MHz spectrometer, with a typical run time of about 8 h (∼5000 transients). IR Spectra Acquisition. IR spectra of p-SWNT and 1 were taken from KBr pellets. Compound 2 was prepared by sonicating (30 min) a small amount (∼0.5 mg) in DMF, and the IR was taken as a solution on NaCl plates. IR spectra were obtained on a Nicolet Prote´ge´ 460. Acknowledgment. We acknowledge the National Science Foundation, the Ford Foundation, the Oklahoma Center for the Advancement of Science and Technology, and the Sloan Foundation for support of this research. We are grateful to SouthWest NanoTechnologies (www.swnano.com) for a generous donation of pristine single-walled carbon nanotubes, synthesized by using its patented CoMoCat process. We are grateful to Ruibo Li for carrying out some preliminary experiments. References and Notes (1) Iijima, S. Nature 1991, 354, 56. (2) Iijima, S.; Ichihashi, T. Nature 1993, 363, 603. (3) (a) Kishinevsky, S.; Nikitenko, S.; Pickup, D.; van-Eck, E.; Gedanken, A. Chem. Mater. 2002, 14, 4498. (b) Simon, F.; Kramberger, Ch.; Pfeiffer, R.; Kuzmany, H.; Zo´lyomi, V.; Ku¨rti, J.; Singer, P.; Alloul, H. Phys. ReV. Lett. 2005, 95, 017401-1. (c) Romaneko, K.; Fonseca, A.; Dumonteil, S.; Nagy, J.; d’Espinose, de Lacaillerie, J.; Lapina, O.; Fraissard, J. J. S. S. NMR 2005, 28, 135. (d) Kneller, J.; Soto, R.; Surber, S.; Colomer, J.; Fonseca, A.; Nagy, J.; Van, Tendeloo, G.; Pietrass, T. J. Am. Chem. Soc. 2000, 122, 10591. (4) (a) Wu, H.; Yang, Y.; Ma, C.; Kuan, H. J. Polym. Sci. 2005, 43, 6084. (b) Xu, M.; Huang, Q.; Chen, Q.; Pingsheng, G.; Sun, Z. Chem. Phys. Lett. 2003, 375, 598. (c) Jiang, G.; Wang, L.; Chen, C.; Dong, X.; Chen, T.; Yu, H. Mater. Lett. 2005, 59, 2085. (5) (a) Maurin, G.; Bousquet, C.; Henn, F.; Bernier, P.; Almairac, R.; Simon, B. Chem. Phys. Lett. 1999, 312, 14. (b) Marques, M.; d’Avezac, M.; Mauri, F. APS 2006, 1, 0510197. (c) Singer, P.; Wzietek, P.; Alloul, H.; Simon, F.; Kuzmany, H. APS 2006, 1, 0510195. (d) Zolyomi, V.; Rusznya´k, A.; Ku¨rti, J.; Gali, A.; Simon, F.; Kuzmany, H.; Szabados, A.; Surja´n, P. Phys. Status Solidi B 2006, 243, 3476. (6) Zurek, E.; Autschabch, J. J. Am. Chem. Soc. 2004, 126, 13079. (7) Besley, N.; Titman, J.; Wright, M. J. Am. Chem. Soc. 2005, 127, 17948. (8) Marques, M.; d’Avezac, M.; Mauri, F. Phys. ReV. B 2006, 73, 125433-1. (9) Matsuo, Y.; Tahara, K.; Nakamura, E. Org. Lett. 2003, 5, 3181. (10) Latil, S.; Henrard, L.; Goze, Bac, C.; Bernier, P.; Rubio, A. Phys. ReV. Lett. 2001, 86, 3160. (11) Tang, X.; Kleinhammes, A.; Shimoda, H.; Fleming, L. Science 2000, 288, 492. (12) Goze, Bac, C.; Latil, S.; Vaccarini, L.; Bernier, P.; Gaveau, P.; Tahir, S.; Micholet, V.; Aznar, R.; Rubio, A.; Metenier, K.; Beguin, F. Phys. ReV. B 2001, 63, 100302-1. (13) Hayashi, S.; Hoshi, F.; Ishikura, T.; Yumura, M.; Ohshima, S. Carbon 2003, 41, 3047. (14) Urban, M.; Konya, Z.; Mehn, D.; Kiricsi, I. J. Mol. Struct. 2005, 744, 93.
J. Phys. Chem. C, Vol. 111, No. 48, 2007 17877 (15) Blackburn, J.; Yan, Y.; Engtrakul, C.; Parilla, P.; Jones, K.; Gennett, T.; Dillon, A.; Heben, M. Chem. Mater. 2006, 18, 2558. (16) Perez-Cabero, M.; Rodriguez-Ramos, I.; Overweg, A.; Sobrados, I.; Sanz, J.; Guerrero-Ruiz, A. Carbon 2005, 43, 2631. (17) Geng, H.; Zhang, X.; Mao, S.; Kleinhammes, A.; Shimoda, H.; Wu, Y.; Zhou, O. Chem. Phys. Lett. 2004, 399, 109. (18) Shen, K.; Pietrass, T. Appl. Phys. Lett. 2004, 84, 1567. (19) Shen, K.; Curran, S.; Dewald, J.; Pietrass, T. AIP Conf. Proc. 2005, 786, 275. (20) Shen, K.; Pietrass, T. Solid State NMR 2006, 29, 125. (21) Kleinhammes, A.; Mao, S.; Yang, X.; Tang, X.; Shimoda, H.; Lu, J.; Zhou, O.; Wu, Y. Phys. ReV. B 2003, 68, 075418-1. (22) Ghosh, S.; Ramanathan, V.; Sood, A. Europhys. Lett. 2004, 65, 678. (23) Clewett, C.; Pietrass, T. J. Phys. Chem. B 2005, 109, 17907. (24) Mao, S.; Kleinhammes, A.; Wu, Y. Chem. Phys. Lett. 2006, 421, 513. (25) Sekaneh, W.; Mrignayani, K.; Dettlaff-Weglikowska, U.; Veeman, W. Chem. Phys. Lett. 2006, 428, 143. (26) Matsuda, K.; Hibi, T.; Kadowaki, H.; Maniwa, Y. Phys. ReV. B 2006, 74, 073415-1. (27) Schmid, M.; Goze-Bac, C.; Mehring, M.; Roth, S. AIP Conf. Proc. 2005, 786, 202. (28) Schmid, M.; Goze-Bac, C.; Mehring, M.; Roth, S.; Bernier, P. AIP Conf. Proc. 2003, 685, 131. (29) Schmid, M.; Goze-Bac, C.; Kramer, S.; Roth, S.; Mehring, M.; Mathis, C.; Petit, P. Phys. ReV. B 2006, 74, 073416-1. (30) Shimoda, H.; Gao, B.; Tang, X.; Kleinhammes, A.; Fleming, L.; Wu, Y.; Zhou, O. Phys. ReV. Lett. 2002, 88, 015502-1. (31) Schmid, M.; Goze-Bac, C.; Mehring, M.; Roth, S.; Bernier, P. AIP Conf. Proc. 2004, 723, 181. (32) Schmid, M.; Goze-Bac, C.; Mehring, M.; Roth, S.; Bernier, P. Mater. Res. Soc. Symp. Proc. 2003, 772, 135. (33) Gao, C.; Liu, M.; Huang, H.; Yin, G.; Xu, Z. Hanneng Cailio 2004, 12, 534. (34) Star, A.; Stoddart, J.; Steuerman, D.; Diehl, M.; Boukai, A.; Wong, E.; Yang, X.; Chung, S-W.; Choi, H.; Heath, J. Angew. Chem., Int. Ed. 2001, 40, 1721. (35) Kitaygorodskiy, A.; Wang, W.; Xie, S.; Lin, Y.; Fernando, S.; Wang, X.; Qu, L.; Chen, B.; Sun, Y. J. Am. Chem. Soc. 2005, 127, 7517. (36) Owens, F.; Jayakody, J.; Greenbaum, S. Compos. Sci. Technol. 2006, 66, 1280. (37) Sun, Y.; Huang, W.; Lin, Y.; Fu, K.; Kitaygorodskiy, A.; Riddle, L.; Yu, Y.; Carroll, D. Chem. Mater. 2001, 13, 2864. (38) Cahill, L.; Yao, Z.; Adronov, A.; Penner, J.; Moonoosawmy, K.; Kruse, P.; Goward, G. J. Phys. Chem. B 2004, 108, 11412. (39) Ju, S.; Utz, M.; Luo, Z.; Papadimitrakopoulos, F. Polym. Prepr. 2005, 46, 209. (40) Qu, L.; Lin, Y.; Hill, D.; Zhou, B.; Wang, W.; Sun, X.; Kitaygorodskiy, A.; Suarez, M.; Connell, J.; Allard, L.; Sun, Y. Macromolecules 2004, 37, 6055. (41) Putz, K.; Mitchell, C.; Krishnamoorti, R.; Green, P. J. Polym. Sci. B 2004, 42, 2286. (42) Nakashima, N.; Tomonari, Y.; Murakami, H. Chem. Lett. 2002, 31, 638. (43) Li, H.; Zhou, B.; Lin, Y.; Gu, L.; Wang, W.; Shiral, Fernando, K.; Kumar, S.; Allard, L.; Sun, Y-P. J. Am. Chem. Soc. 2004, 126, 1014. (44) Banerjee, S.; Wong, S. J. Am, Chem. Soc. 2002, 124, 8940. (45) (a) Hamon, M.; Chen, J.; Hu, H.; Chen, Y.; Itkis, M.; Rao, A.; Eklund, P.; Haddon, R. AdV. Mater. 1999, 11, 834. (b) Zhang, J.; Wnag, G.; Shon, Y.; Zhou, O.; Superfine, R.; Murray, R. J. Phys. Chem. B 2003, 107, 3726. (c) Ru¨ther, M.; Frehill, F.; O’Brien, J.; Minnet, A.; Blau, W.; Vos, J.; in het Pnahuis, M. J. Phys. Chem. B 2004, 108, 9665. (d) Zhang, J.; Wang, G.; Shon, Y-S.; Zhou, O.; Superfine, R.; Murray, R. J. Phys. Chem. B 2003, 107, 3726. (46) Umek, P.; Seo, J.; Hernadi, K.; Mrzel, A.; Pechy, P.; Mihailovic, D.; Forr´o, L. Chem. Mater. 2003, 15, 4751. (47) Holzinger, M.; Vostrowsky, O.; Hirsch, A.; Hennrich, F.; Kappes, M.; Weiss, R.; Jellen, F. Angew. Chem., Int. Ed. 2001, 40, 4002. (48) Liang, F.; Alemany, L.; Beach, J.; Billups, W. J. Am. Chem. Soc. 2005, 127, 13941. (49) Hemraj-Benny, T.; Wong, S. Chem. Mater. 2006, 18, 4827. (50) Engtrakul, C.; Davis, M.; Gennett, T.; Dillon, A.; Jones, K.; Heben, M. J. Am. Chem. Soc. 2005, 127, 17548. (51) Zhang, L.; Yang, J.; Edwards, C.; Alemany, L.; Khabasheka, V.; Barron, A. Chem. Commun. 2005, 26, 3265. (52) Delgado, J.; de la Cruz, P.; Langa, F.; Urbina, A.; Casado, J.; Navarrete, J. Chem. Commun. 2004, 15, 1734. (53) Holzinger, M.; Abraham, J.; Whelan, P.; Graupner, R.; Ley, L.; Hennrich, F.; Kappes, M.; Hirsch, A. J. Am. Chem. Soc. 2003, 125, 8566. (54) Yinghaui, Z.; Pneg, A.; Carpenter, K.; Maguire, J.; Hosmane, N.; Takagaki, M. J. Am. Chem. Soc. 2005, 127, 9875.
17878 J. Phys. Chem. C, Vol. 111, No. 48, 2007 (55) Coleman, K.; Bailey, S.; Fogden, S.; Green, M. J. Am. Chem. Soc. 2003, 125, 8722. (56) Alvaro, M.; Atienzar, P.; de la Cruz, P.; Delgado, J.; Garcia, H.; Langa, F. J. Phys. Chem. B 2004, 108, 12691. (57) Alvaro, M.; Atienzar, P.; de la Cruz, P.; Delgado, J.; Troiani, V.; Garcia, H.; Langa, F.; Palkar, A.; Echegoyen, L. J. Am. Chem. Soc. 2006, 128, 6626. (58) Dyke, C.; Tour, J. J. Am. Chem. Soc. 2003, 125, 1156. (59) (a) Bahr, J.; Tour, J. Chem. Mater. 2001, 13, 3823. (b) Bahr, J.; Tour, J. J. Mater. Chem. 2002, 12, 1952. (c) Bahr, J.; Yang, J.; Kosynkin, D.; Broniskowski, M.; Smalley, R.; Tour, J. J. Am. Chem. Soc. 2001, 123, 6536. (d) Dyke, C.; Tour, J. Nano Lett. 2003, 3, 1215. (60) Synthesized by the patented CoMoCatTM process; available from SouthWest NanoTechnologies, Inc., 2360 Industrial Blvd., Norman, OK. 73069-8518; (405) 217-8388. (61) Hennrich, F.; Kupke, R.; Lebedkin, S.; Arnold, K.; Fisher, R.; Resasco, D.; Kappes, M. J. Phys. Chem. B 2005, 109, 10567.
Nelson et al. (62) (a) Kim, P.; Odom, T.; Huang, J.; Lieber, C. Electronic Structure of Single Walled Nanotubes: van Hove Singularities and End States. Materials Research Society (MRS) 1998 Fall Meeting, Symposium S Carbon Nanotubes, Fullerenes and Related Carbon Materials, Boston, MA, Dec 2, 1998. (b) Kim, P.; Odom, T.; Huang, J.; Lieber, C. Phys. ReV. Lett. 1999, 82, 1225. (c) Moniruzzaman, M.; Winey, K. Macromolecules 2006, 39 (16), 5194-5205. (63) (a) Yanagisawa, M.; Hayamizu, K.; Yamamoto, O. Magn. Reson. Chem. 1987, 25, 184. (b) IR data were found on the Spectra DataBase System (www.aist.go.jp/RIODB/SDBS/cgi-bin/cre_index.cgi) by keyword searches on compound names. (c) Swift, J. A. et al. Chem. Mater. 2004, 16, 4948. (d) Heiss, C.; Cottet, F.; Schlosser, M. Eur. J. Org. Chem. 2005, 71, 5236. (e) Marcus, S.; Miller, S. J. Phys. Chem. 1964, 68, 331. (64) Kra´tky, V.; Kra´lik, M.; Kaszonyi, A.; Stolcova, M.; Zalibera, L.; Meca´rova´, M.; Hronec, M. Collect. Czech. Chem. Commun. 2003, 68, 1819. (65) Testaferri, L.; Tiecco, M.; Tingoli, M.; Chainelli, D.; Montanucci, M. Synthesis 1983, 13, 751.
