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Langmuir 1997, 13, 1672-1676
Surface and Optical Properties of Langmuir and LB Films of a Crown-Ether C60 Derivative Shaopeng Wang, Roger M. Leblanc,* Francisco Arias, and Luis Echegoyen* Department of Chemistry, University of Miami, Coral Gables, Florida 33124 Received October 2, 1996X The Langmuir and Langmuir-Blodgett films of a benzo-18-crown-6-methanofullerene (1) were studied by spectrophotometry and Bre¨wster angle microscopy. The surface pressure-area isotherm of the C60 derivative (1) was obtained, and the compressibility of the isotherms was calculated. The addition of KCl to the water subphase stabilized the monolayer and increased the limiting area per molecule from 84 to 101 Å, which is near the theoretical value. The changes of the Langmuir monolayer UV-vis spectra as a function of time are considered to be due to fullerene aggregation. Polymerization was not detected upon UV irradiation, in contrast to what has been reported in the literature. Bre¨wster angle microscopy shows different aggregation properties of the benzo-18-crown-6-methanofullerene (1) Langmuir monolayers on pure water compared to those on a 1 M KCl subphase.
1. Introduction The first large scale synthesis of C60 reported by Kra¨tschmer et al.1 was followed by extensive studies on the chemical properties of the spherical molecule. C60 can be derivatized using a variety of organic reactions. For instance, many fullerene derivatives have been prepared by nucleophilic addition, cycloaddition, hydrogenation, and radical addition.2 Such versatility has led to the use of C60 in the synthesis of polymers. Some studies have confirmed the formation of “pearl necklace” polymers which have fullerene molecules as part of the polymer backbone.3 Furthermore, “charm bracelet” polymers in which the fullerenes are pendant groups on the side chain of the polymer have also been reported.3 Moreover, the polymerization of C60 itself has been studied quite extensively. Several fullerene polymers have been reported in which pure C60 has been polymerized by applying intense UV-vis radiation in an oxygen-free environment,4 using very high pressures,5 electron stimulation,6 or ion bombardment.7 In addition, C60 has been reported to aggregate in toluene when large amounts of acetonitrile are added; these aggregates have presumably been polymerized via intense UV-vis irradiation.8 Alternatively, Pekker and co-workers9 have found that C60 anions in the orthorhombic phase of A1C60, where A * To whom correspondence should be addressed. Fax: (305) 2844571. Phone: (305) 284-2282. E-mail:
[email protected]. miami.edu. X Abstract published in Advance ACS Abstracts, February 1, 1997. (1) Kra¨tschmer, W.; Lamb, L. D.; Fostiropoulos, K.; Huffman, D. R. Nature 1990, 347, 354. (2) Hirsch, A. The chemistry of the fullerenes; Thieme: New York, 1994. (3) Mirkin, C. A.; Caldwell, W. B. Tetrahedron 1996, 52, 5113. (4) (a) Rao, A. M.; Zhou, P.; Wang, K. A.; Hager, T.; Holden, J. M.; Wang, Y.; Lee, T.; Bi, X. X.; Eklund, P. C.; Cornett, D. S.; Duncan, M. A.; Amster, I. J. Science 1993, 259, 955. (b) Cornett, D. S.; Amster, J.; Duncan, A. M.; Rao, A. M.; Eklund, P. C. J. Phys. Chem. 1993, 97, 5036. (c) Ito, A.; Morikawa, T.; Takahashi, T. Chem. Phys. Lett. 1993, 211, 333. (5) (a) Iwasa, N.; Arima, T.; Fleming, R. M.; Siegrist, T.; Zhou, O.; Haddon, R. C.; Rothberg, L. J.; Lyons, K. B.; Carter, H. L., Jr.; Herbard, A. F.; Tycko, K.; Dabbagh, G.; Krajewnski, J. J.; Thomas, G. A.; Yagi, T. Science 1994, 264, 1570. (b) Oszlangi, G.; Forro, L. Solid State Commun. 1995, 94, 265. (6) Zhao, Y. B.; Poirier, D. M.; Pechman, R. J.; Weaver, J. H. Appl. Phys. Lett. 1994, 64, 577. (7) (a) Kastner, J.; Kuzmany, H.; Palmetshofer, L. Appl. Phys. Lett. 1994, 65, 543. (b) Palmetshofer, L.; Kastner, J. Nucl. Instrum. Methods Phys. Res., Sect. B 1995, 96, 343. (8) Sun, Y. P.; Bin, M.; Bunker, C. E.; Liu, B. J. Am. Chem. Soc. 1995, 117, 12705.
S0743-7463(96)00951-1 CCC: $14.00
can be K, Rb, or Cs, polymerize by ionically induced reversible [2 + 2] cycloaddition at ∼400 K. The crystalline polymers could not be dissolved in a wide variety of organic solvents. The separations between the centers of the C60 molecules were estimated to be 0.37 Å2 shorter than those measured for the unreacted fullerides, suggesting the formation of C-C bonds. Since the work reported here involves the irradiation of Langmuir films of a crown ether C60 derivative, other related reports are briefly discussed now. Fullerene monolayers have been obtained by different approaches. Self-assembly of fullerene molecules has been achieved either by the reaction of C60 with the functional groups of a modified metal surface10 or by the derivatization of C60 with a functional group that can react or interact with the metal surface.11,12 A different approach has been to use LB troughs to compress the amphiphilic fullerene derivative molecules until monolayers are formed at the airwater interface.13-17 Good quality films of pure C60 are difficult to obtain following this procedure, since C60 is not an amphiphilic molecule and easily aggregates to form multilayer films due to its strong hydrophobic interaction; (9) (a) Pekker, S.; Ja´nossy, A.; Mihaly, L.; Chauvet, O.; Carrard, M.; Forro´, L. Science 1994, 265, 1077. (b) Stephens, P. W.: Bortel, G.; Faigel, G.; Tegze, M.; Ja´nossy, A.; Pekker, S.; Oszlanyl, G.; Forro´, L. Nature 1994, 370, 636. (10) (a) Chen, K.; Caldwell, W. B.; Mirkin, C. A. J. Am. Chem. Soc. 1993, 115, 1193. (b) Chupa, J. A.; Xu, S.; Fischetti, R. F.; Strogin, R. M.; McCauley, J. P., Jr.; Smith, A. B., III; Blasie, J. K.; Peticolas, L. J.; Bean, J. C. J. Am. Chem. Soc. 1993, 115, 4383. (11) Caldwell, W. B.; Chen, K.; Herr, B. R.; Mirkin, C. A.; Hulteen, J. C.; Van Duyne, R. P. Langmuir 1994, 10, 4109. (12) Arias, F.; Godinez, L. A.; Wilson, S. R.; Kaifer, A. E.; Echegoyen, L. J. Am. Chem. Soc. 1996, 118, 6086. (13) Jonas, U.; Cardullo, F.; Belik, P.; Diederich, F.; Gu¨gel, A.; Harth, E.; Herrmann, A.; Issacs, L.; Mu¨llen, K.; Ringsdorf, H.; Thilgen, C.; Uhlmann, P.; Vasella, A.; Waldraff, C. A. A.; Walter, M. Chem. Eur. J. 1995, 1, 243. (14) (a) Back, R.; Lennox, R. B. J. Phys. Chem. 1992, 96, 8149. (b) Xiao, Y.; Yao, Z.; Jin, D. J. Phys. Chem. 1994, 98, 5557. (c) Brousseau, J. L.; Tian, K.; Gauvin, S.; Leblanc, R. M.; Delhae`s, P. Chem. Phys. Lett. 1993, 202, 521. (15) (a) Matsumoto, M.; Tachibana, H.; Azuni, R.; Tanaka, M.; Nakamura, T.; Yunome, G.; Abe, M.; Yamago, S.; Nakamura, E. Langmuir 1995, 11, 660. (b) Diederich, F.; Jonas, U.; Gramlich, V.; Herrmann, A.; Ringsdorf, H.; Thilgen, C. Helv. Chim. Acta 1993, 76, 2445. (c) Leigh, D. A.; Moody, A. E.; Wade, F. A.; King, T. A.; West, D.; Bahra, G. S. Langmuir 1995, 11, 2334. (16) (a) Zhang, X.; Zhang, R.; Shen, J.; Zou, G. Macromol. Rapid Commun. 1994, 15, 373. (b) Bulho˜es, L. O. S.; Obeng, Y. S.; Kim, Y. T.; Zhou, F.; Bard, A. J. Chem. Mater. 1993, 5, 110. (c) Jehoulet, C.; Obeng, Y. S.; Kim, Y. T.; Zhou, F.; Bard, A. J. Am. Chem. Soc. 1992, 114, 4237. (17) ((a) Obeng, Y. S.; Bard, A. J. J. Am. Chem. Soc. 1991, 113, 6279. (b) Maliszewskyj, N. C.; Heiney, P. A.; Jones, D. R.; Strogin, R. M.; Cichy, M. A.; Smith, A. B. Langmuir 1993, 9, 1439.
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Films of a Crown-Ether C60 Derivative
e.g., pristine C60 was found to form multilayer films at the air-water interface with limiting areas of ∼20 Å2/ molecule.14 However, two research groups have reported that Langmuir monolayers can be formed with very dilute C60 solutions (
