pubs.acs.org/Langmuir © 2009 American Chemical Society
Selective Formation and Structural Properties of Rhombic Dodecahedral [70]Fullerene Microparticles Formed by Reaction with Aliphatic Diamines Ken-ichi Matsuoka,† Tsuyoshi Akiyama,*,†,‡ and Sunao Yamada*,†,‡ †
Department of Materials Physics and Chemistry, Graduate School of Engineering and ‡Department of Applied Chemistry, Faculty of Engineering, Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan Received September 7, 2009. Revised Manuscript Received October 22, 2009
We have accomplished the selective formation of rhombic dodecahedral microparticles on the submicrometer to micrometer scale by the reaction of [70]fullerene (C70) with primary aliphatic diamines. The morphology of the resultant microparticles was analyzed by scanning electron microscopy, powder X-ray diffraction, and other spectroscopic methods, demonstrating that the resultant particles held a rhombic dodecahedral shape having a simple cubic lattice structure and that primary aliphatic amines were mostly trapped inside the particles through electronic interaction between C70 and amines. Furthermore, we have discovered interesting structural characteristics in which the incorporated amines could be removed from the C70 microparticles or exchanged with other primary aliphatic diamines.
Introducton Because of high electron affinity,1 high carrier mobility,2 low reorganization energy,3 and optical properties,4 fullerenes have been considered to be a promising nanocarbon material in a wide variety of applications such as solar cells,5 field-effect transistors,2 catalysts,6 and biological tools.7 Another utility of fullerenes is their attractive interactions with various organic,8-17 organometallic,17 (1) Reed, C. A.; Bolskar, R. D. Chem. Rev. 2000, 100, 1075. (2) Anthopoulos, T. D.; Singh, B.; Marjanovic, N.; Sariciftci, N. S.; Ramil, A. M.; C€olle, M.; de Leeuw, D. M. Appl. Phys. Lett. 2006, 89, 213504. (3) (a) Imahori, H.; Sakata, Y. Adv. Mater. 1997, 9, 537. (b) Imahori, H.; Sakata, Y. Eur. J. Org. Chem. 1999, 2445. (4) Tutt, L. W.; Kost, A. Nature 1992, 356, 225. (5) (a) G€unes, S.; Neugebauer, H.; Sariciftci, N. S. Chem. Rev. 2007, 107, 1324. (b) Thompson, B. C.; Frechet, J. M. J. Angew. Chem., Int. Ed. 2008, 47, 58. (6) (a) Jensen, A. W.; Maru, B. S.; Zhang, X.; Mohanty, D. K.; Fashlman, B. D.; Swanson, D. R.; Tomalia, D. A. Nano Lett. 2005, 5, 1171. (b) Hino, T.; Anzai, T.; Kuramoto, N. Tetrahedron Lett. 2006, 47, 1429. (c) Matsuo, Y.; Uematsu, T.; Nakamura, E. Eur. J. Inorg. Chem. 2007, 2729. (7) (a) Higashi, N.; Inoue, T.; Niwa, M. Chem. Commun. 1997, 1507. (b) Nakamura, E.; Isobe, H.; Tomita, N.; Sawamura, M.; Jinno, S.; Okayama, H. Angew. Chem., Int. Ed. 2000, 39, 4254. (c) Ikeda, A.; Doi, Y.; Hashizume, M.; Kikuchi, J.; Konishi, T. J. Am. Chem. Soc. 2007, 129, 4140. (8) Jinno, K.; Yamamoto, K. J. Microcolumn Sep. 1992, 4, 187. (9) Jinno, K.; Fukuoka, K.; Fetzer, J. C.; Biggs, W. R. J. Microcolumn Sep. 1993, 5, 517. (10) Stalling, D. L.; Kenneth, C. G.; Kuo, C.; Saim, S. J. Microcolumn Sep. 1993, 5, 223. (11) Jinno, K.; Tanabe, K.; Saito, Y.; Nagashima, H. Analyst 1997, 122, 787. (12) Glausch, A.; Hirsch, A.; Lamparth, I.; Schurig, V. J. Chromatogr., A 1998, 809, 252. (13) Kartsova, L. A.; Makarov, A. A. J. Anal. Chem. 2004, 59, 812. (14) Hayashi, A.; Yamamoto, S.; Suzuki, K.; Matsuoka, T. J. Mater. Chem. 2004, 14, 2633. (15) Berezkin, V. I.; Viktorovski, I. V.; Vul’, A. Y.; Golubev, L. V.; Petrova, V. N.; Khoroshko, L. O. Semiconductors 2003, 37, 802. (16) Chen, C.; Chen, J.; Wang, X.; Liu, S.; Sheng, G.; Fu, J. J. Chromatogr., A 2000, 886, 313. (17) Ballesteros, E.; Gallego, M.; Valcarcel, M. J. Chromatogr., A 2000, 869, 101. (18) Gallego, M.; de Pe~na, Y. P.; Valcarcel, M. Anal. Chem. 1994, 6, 4074. (19) de Pe~na, Y. P.; Gallego, M.; Valcarcel, M. J. Anal. At. Spectrom. 1997, 12, 453. (20) Samonin, V. V.; Nikonova, V. Y.; Podvyaznikov, M. L. Russ. J. Phys. Chem. A 2008, 82, 1371. (21) Vallant, R. M.; Szabo, Z.; Trojer, L.; Najam-ul-Haq, M.; Rainer, M.; Huck, C. W.; Barkry, R.; Bonn, G. K. J. Proteome Res. 2007, 6, 44. (22) Vallant, R. M.; Szabo, Z.; Bachmann, S.; Bakry, R.; Najam-ul-Haq, M.; Rainer, M.; Heigl, N.; Petter, C.; Huck, C. W.; Bonn, G. K. Anal. Chem. 2007, 79, 8144.
4274 DOI: 10.1021/la903355e
and inorganic18-20 species as well as biomolecules21-23 based on π-π, van der Waals, and donor-acceptor interactions. Such attractive forces allow fullerenes and their derivatives to adsorb chemical compounds at a certain strength, and fullerenes have been considered to be peculiar candidates for use in chromatographic stationary phases, extraction tools, and adsorbents.8-23 In addition, fullerenes form a wide range of functional architectures and controlled morphologies upon the inclusion of partners such as solvents,24 electron donors,25 and others26 as a result of chemical and/or structural affinities. For instance, several groups have reported the syntheses of shape-controlled fullerene nanocrystals of wires,24a rods,24b,24d sheets,24c and many others24d through fullerene-solvent interactions, where solvents were often incorporated into the crystals to form fullerene solvates. Accordingly, guest molecules trapped inside of fullerene assemblies act as one of the key factors determining their growth characteristics,24 internal structures,24-26 and physical properties.24b,25a One may consider the desorption properties of guest molecules from fullerene assemblies to be an interesting structural aspect in the manipulation of molecular assemblies. In some cases, guest molecules such as ferrocene25b or even a large macrocycle26c can be removed from fullerene frameworks by heat treatment or the use of appropriate solvents, leading to different structural and physical properties. According to the related studies, many of them have focused on the adsorption and/or inclusion properties of fullerenes and related products, though little attention has been paid to the (23) Chen, H.; Qi, D.; Deng, C.; Tang, P.; Zhang, X. Proteomics 2009, 9, 380. (24) (a) Geng, J.; Zhou, W.; Skelton, P.; Yue, W.; Kinloch, I. A.; Wndle, A. H.; Johnson, B. F. G. J. Am. Chem. Soc. 2008, 130, 2527. (b) Wang, L.; Yu, B.; Yao, M.; Liu, D.; Hou, Y.; Sundqvist, B.; You, H.; Zhang, D.; Ma, D. Chem. Mater. 2006, 18, 4190. (c) Sathish, M.; Miyazawa, K.; Hill, J. P.; Ariga, K. J. Am. Chem. Soc. 2009, 131, 6372. (d) Masuhara, A.; Tan, Z.; Kasai, H.; Nakanichi, H.; Oikawa, H. Jpn. J. Appl. Phys. 2009, 48, 050206. (25) (a) Konarev, D. V.; Lyubovskaya, R. N.; Drichko, N. V.; Yudanova, E. I.; Shul’ga, Y. M.; Litvinov, A. L.; Semkin, V. N.; Tarasov, B. P. J. Mater. Chem. 2000, 10, 803. (b) Wakahara, T.; Sathish, M.; Miyazawa, K.; Hu, C.; Tateyama, Y.; Nemoto, Y.; Sasaki, T.; Ito, O. J. Am. Chem. Soc. 2009, 131, 9940. (26) (a) Makha, M.; Purich, A.; Raston, C. L.; Sobolev, A. N. Eur. J. Inorg. Chem. 2006, 507. (b) Hardie, M. J.; Raston, C. L. Chem. Commun. 1999, 1153. (c) Makha, M.; Evans, C. W.; Sobolev, A. N.; Raston, C. L. Cryst. Growth Des. 2008, 8, 2929.
Published on Web 11/11/2009
Langmuir 2010, 26(6), 4274–4280
Matsuoka et al.
Article
desorbing25b,26c and exchanging behavior of chemical species trapped inside of fullerene assemblies. From the viewpoints of basic science and potential applications of fullerene-based functional architectures, it is intriguing yet challenging to create a smart system of the fullerene-based medium capable of releasing or exchanging accommodated chemical compounds with external environments. Meanwhile, the chemistry between fullerenes (electron acceptors) and aliphatic amines (electron donors) has had a long history since the amination reaction of fullerene by primary/ secondary aliphatic amines was first reported by Wudl et al.27 The reaction of fullerene with primary/secondary aliphatic amines readily produces amino derivatives of fullerenes presumably via a single electron-transfer process to form ion pairs and subsequent covalent bonds. This reaction is one of the first synthesis reactions in fullerene chemistry to offer a wide variety of fullerene derivatives27-41 including polymer-42 and dendrimer-bound6a fullerenes. Surface modifications of silica gel,6b (semi)conducting substrates,43 and metal nanoparticles44 with fullerenes were also achieved with the aid of the amination reactions. In addition, multiple hydrogenation of fullerenes was recently achieved by the utilization of polyamine species.45 Accordingly, most of the related studies on the reactions between fullerenes and aliphatic amines are based on the bond-forming reaction, surface chemistry, and/or spectroscopic analysis of the electron-transfer (or charge-transfer) process in the liquid phase.46-51
Recently, we unexpectedly observed the formation of rhombic dodecahedral particles of C70 as a result of the reaction with 1,2diaminoethane (DAE) when an excess amount (1000 equiv) of DAE was present in the system under a specific condition.52 It is remarkable because treating fullerene with excess aliphatic amines often inevitably generates complicated mixtures of fullereneamine adducts,27-30 and it is noteworthy that although C60 preferentially generated submicrometer spherical particles with amorphous structures by reaction with DAE, C70 exclusively formed rhombic dodecahedral particles with an ordered structure (simple cubic lattice) under quite similar conditions.52 The ordered assembly of molecular components into tailormade structures will be a challenging issue in basic science with respect to discovering novel functionalities and technological applications.24-26,53 Hence, the main purpose of this study is to clarify the peculiar assembly behavior of C70 through its interaction with aliphatic amines. We found that C70 and primary aliphatic diamines (PADs), such as DAE, 1,3-diaminopropane (DAPr), 1,4-diaminobutane (DAB), and 1,5-diaminopentane (DAPe), led to the selective formation of rhombic dodecahedral (submicrometer to micrometer) particles mainly via donoracceptor complexation between PADs and C70. Furthermore, we discovered that the C70-PAD particles had the capability to release and exchange guest molecules (PADs) into the external environment.
(27) (a) Wudl, F.; Hirsch, A.; Khemani, K. C.; Suzuki, T.; Allemand, P.-M.; Koch, H. E.; Srdanov, G.; Webb, H. M. Fullerenes: Synthesis, Properties and Chemistry of Large Carbon Clusters. In ACS Symposium Series; Hammond, G. S., Kuck, V. J., Eds.; American Chemical Society: Washington, DC, 1992; Vol. 48, Chapter 11, pp 161-175.(b) Hirsch, A.; Li, Q.; Wudl, F. Angew. Chem., Int. Ed. 1991, 30, 1309. (28) Miller, G. P. C. R. Chim. 2006, 6, 952. (29) Sesharri, R.; Govindaraj, A.; Nagarajan, R.; Pradeep, T.; Rao, C. N. R. Tetrahedron Lett. 1992, 33, 2069. (30) Kampe, K.-D.; Egger, N.; Vogel, M. Angew. Chem., Int. Ed. Engl. 1993, 32, 1174. (31) Davey, S. N.; Leigh, D. A.; Moody, A. E.; Tettler, L. W.; Wade, F. A. J. Chem. Soc., Chem. Commun. 1994, 397. (32) Schick, G.; Kampe, K.-D; Hirsch, A. J. Chem. Soc., Chem. Commun. 1995, 2023. (33) Balch, A. L.; Cullison, B; Fawcett, W. R.; Ginwalla, A. S.; Olmstead, M. M.; Wnkler, K. J. Chem. Soc., Chem. Commun. 1995, 2287. (34) Butts, C. P.; Jazdzyk, M. Chem. Commun. 2003, 1530. (35) Isobe, H.; Ohbayashi, A.; Sawamura, M.; Nakamura, E. J. Am. Chem. Soc. 2000, 122, 2669. (36) Isobe, H.; Tomita, N.; Nakamura, E. Org. Lett. 2000, 2, 3663. (37) Isobe, H.; Tanaka, T.; Nakanishi, W.; Lemiegre, L.; Nakamura, E. J. Org. Chem. 2005, 70, 4826. (38) Balch, A. L.; Ginwalla, A. S.; Olmstead, M. M. Tetrahedron 1996, 52, 5021. (39) Troshina, O. A.; Troshin, P. A.; Peregudov, A. S.; Lyubovskaya, R. N. Org. Biomol. Chem. 2006, 4, 1647. (40) Troshina, O. A.; Troshin, P. A.; Peregudov, A. S.; Kozlovski, V. I.; Lyubovskaya, R. N. Eur. J. Org. Chem. 2006, 5243. (41) Lemiegre, L.; Tanaka, T.; Nanao, T.; Isobe, H.; Nakamura, E. Chem. Lett. 2007, 36, 20. (42) Geckeler, K. E.; Hirsch, A. J. Am. Chem. Soc. 1993, 115, 3850. (43) (a) Caldwell, W. B.; Chen, K.; Mirkin, C. A.; Babinec, S. J. Langmuir 1993, 9, 1945. (b) Chen, K.; Caldwell, W. B.; Mirkin, C. A. J. Am. Chem. Soc. 1193, 115, 1193. (c) Akiyama, T.; Matsuoka, K.; Arakawa, T.; Kakurani, K.; Miyazaki, A.; Yamada, S. Jpn. J. Appl. Phys. 2006, 45, 3758. (d) Matsuoka, K.; Akiyama, T.; Yamada, S. J. Phys. Chem. C 2008, 112, 7015. (e) Bustos, E.; Manríquez, J.; Echegoyen, L.; Godínez, L. A. Chem. Commun. 2005, 1613. (44) Shin, S.-M.; Su, W.-F.; Lin, Y.-J.; Wu, C.-S.; Chen, C.-D. Langmuir 2002, 18, 3332. (45) (a) Briggs, J. B.; Montgomery, M.; Silva, L. L.; Miller, G. P. Org. Lett. 2005, 7, 5553. (b) Kintigh, J.; Jonathan, J.; Briggs, B.; Letouneau, K.; Miller, G. P. J. Mater. Chem. 2007, 17, 4647. (46) Lobach, A. S.; Goldshleger, N. F.; Kaplunov, M. G.; Kulikov, A. V. Chem. Phys. Lett. 1995, 243, 22. (47) Lobach, A. S.; Goldshleger, N. F.; Kaplunov, M. G.; Kulikov, A. V. Russ. Chem. Bull. 1996, 45, 93. (48) Qiao, J. L.; Gong, Q. J.; Du, L. M.; Jin, W. J. Spectrochim. Acta, Part A 2001, 57, 17. (49) Li, W. J.; Liang, W. J. Spectrochim. Acta, Part A 2007, 67, 1346. (50) Sun, Y.-P.; Bunker, C. E. J. Phys. Chem. A 1998, 102, 7580. (51) Sun, Y.-P.; Bunker, C. E.; Liu, B. Chem. Phys. Lett. 1997, 272, 25.
Reagents. C70 (purity >99%, MER Co.), DAE (99%,
Experimental Section
Langmuir 2010, 26(6), 4274–4280
Wako), DAE-d4 (98 atom % D, Sigma-Aldrich), DAPr (99%, Aldrich), DAB (95%, Tokyo Kasei), DAPe (95%, Aldrich), 1aminopropane (AP) (98%, Wako), 1,2-diaminopropane (1,2DAPr, 99%, Aldrich), 2,2-dimethyl-1,3-propanediamine (DMDAPr), 99%, Aldrich), and N,N,N0 ,N0 -tetramethyldiaminoethane (TM-DAE) (98%, Wako) were used as received. Instruments. UV-vis-NIR and FTIR spectra (1 cm-1 resolution) of samples were recorded in a KBr matrix by a V-670 spectrophotometer (JASCO) equipped with an integral sphere and an FT/IR 620 (JASCO), respectively. Powder X-ray diffraction (XRD) measurements were carried out by MultiFlex (Rigaku) with monochromatic Cu KR radiation (1.5418 A˚) at room temperature. A range of 2θ = 5-35° was scanned at a rate of 1°/min. Scanning electron microscope (SEM) images were obtained on an S-5000 (Hitachi) with an acceleration voltage of 10 kV using indium-tin oxide-coated glass substrates. X-band electron paramagnetic resonance (EPR) measurements were carried out with a JES-FE1XG (JEOL). Sample Preparation. To 10 mL of a toluene/o-dichlorobenzene (o-DCB) (7:3 v/v) solution containing C70 (16.8 mg, 2.0 10-5 mol) was added 10 mL of a toluene solution containing 2.0 10-2 mol of PAD at one time without mechanical stirring. Reaction temperatures (298 K for DAE, 308 K for DAPr, and 313 K for DAB and DAPe, respectively) were carefully controlled by performing the mixing procedure in a thermostatic bath. Dark precipitates were formed immediately (within 1 s) in all cases and were promptly collected by vacuum filtration and dried in vacuo. Obtained C70-PAD samples are denoted as C70-DAE, C70-DAPr, C70-DAB, and C70-DAPe, respectively.
Results and Discussion Characterization of C70-PAD Microparticles. SEM images of the obtained C70-PAD precipitates are shown in Figure 1. (52) Matsuoka, K.; Matsumura, S.; Akiyama, T.; Yamada, S. Chem. Lett. 2008, 37, 932. (53) (a) Whiteside, G. M.; Grzybowski, B. Science 2002, 295, 2418. (b) Cui, S.; Liu, H.; Gan, L.; Li, Y.; Zhu, D. Adv. Mater. 2008, 20, 2918. (c) Xia, F.; Jiang, L. Adv. Mater. 2008, 20, 2842.
DOI: 10.1021/la903355e
4275
Article
Matsuoka et al.
Figure 2. XRD patterns of C70-PAD particles (a) C70-DAE, (b) C70-DAPr, (c) C70-DAB, and (d) C70-DAPe. * denotes background noise.
Figure 1. SEM images of (a, b) C70-DAE, (c, d) C70-DAPr, (e, f) C70-DAB, and (g, h) C70-DAPe.
They clearly show that all samples are exclusively composed of well-defined rhombic dodecahedral particles of submicrometer to micrometer size in the ranges of 200-500 nm for C70-DAE, 200600 nm for C70-DAPr, 200-1000 nm for C70-DAB, and 6002000 nm for C70-DAPe, respectively. Such an exclusive formation of rhombic dodecahedral microparticles requires well-controlled conditions for the concentration of C70 and PADs, reaction temperature, and solvent composition in the preparation procedure (Figures S1-S5). For instance, when the amount of DAE decreased or increased by 10-fold in the preparation process of C70-DAE, quasi-spherical particles having amorphous structures were slowly formed (Figure S3a,d).49 These quasi-spherical particles were formed much more slowly (1 h to 1 day) than C70-DAE (within 1 s), suggesting the presence of different mechanisms with the amination reactions. We further investigated the effect of the molecular structure of aliphatic amines on the assembly behavior of C70. As representative compounds, a monoamine (AP), branched primary diamines (DM-DAPr and 1,2-DAPr), and a tertiary diamine (TM-DAE) were examined under similar preparation conditions to those of C70-PAD particles. As a result, 1,2-DAPr and C70 slowly generated quasi-spherical particles without an ordered structure as judged from SEM and XRD analysis (Figure S6). No appreciable formation of precipitates was observed for the cases of AP, DMDAPr, and TM-DAE at least within 1 week. These results suggest that the linear molecular structure with two terminal amino 4276 DOI: 10.1021/la903355e
groups in the aliphatic amine species is one of the key factors in generating rhombic dodecahedral particles. Figure 2 shows the XRD patterns of C70-PAD particles. Each sample shows sharp diffraction peaks with nearly identical diffraction patterns. The rhombic dodecahedron holds four 3-fold axes and three 4-fold axes, expressing cubic symmetry of the m3m point group class, and its 12 crystal faces are indexed to {110} planes.54 Accordingly, XRD patterns of all C70-PAD particles are assignable to a simple cubic (sc) lattice structure, where the diffraction peaks are indexed in Figure 2a. The lattice constant gradually increases from a = 10.43 to 10.63 A˚ in the order of C70-DAE < C70-DAPr < C70-DAB < C70-DAPe, which correlates with the molecular size of PADs (Table 1). The obtained XRD spectra were apparently different from those reported in an early study,55 showing that the aggregates of some C60-PAD adducts give broad XRD spectra attributable to amorphous structures. In a pristine C70 crystal, the center-to-center distance between neighboring C70 molecules at 300 K has been reported to be approximately 10.12 A˚, where C70 molecules randomly rotate around major (long) axes and their orientations are parallel to each other.56 If each lattice constant of the C70-PAD particles is taken as the approximate center-to-center distance of neighboring C70, then C70 molecules in C70-PAD microparticles could be located slightly far away (0.3-0.5 A˚) from each other as compared to pristine C70. Molecular composition ratios of C70-PAD microparticles were estimated from elemental analysis (Table 1). On the basis of the C/H/N ratio, the stoichiometry of each C70-PAD particle was close to C70/PAD = 1:3 in all cases. It is thus anticipated that C70PAD particles are likely to be formed by an identical assembly process because they have similar properties with respect to (54) Yu, C.; Tian, B.; Fan, J.; Stucky, G. D.; Zhao, D. J. Am. Chem. Soc. 2002, 124, 4556. (55) Ulug, A.; Mete, A.; Ulug, B. Fullerenes, Nanotubes, Carbon Nanostruct. 1997, 5, 1651. (56) (a) Rao, A. M.; Menon, M.; Wang, K.-A.; Eklund, P. C.; Subbaswamy, K. R.; Cornett, D. S.; Duncan, M. A.; Amster, I. J. Chem. Phys. Lett. 1994, 224, 106. (b) Vaughan, G. B. M.; Heiney, P.; Cox, D. E.; Fischer, J. E.; McGhie, A. R.; Smith, A. L.; Strongin, R. M.; Cichy, M. A.; Smith, A. B., III. Chem. Phys. 1993, 178, 599.
Langmuir 2010, 26(6), 4274–4280
Matsuoka et al.
Article Table 1. Elemental Analysis, Structure, and Size Range of C70-PAD Microparticles
sample
elemental analysis C/H/N
estimated composition C70/PAD
C70-DAE
84.87:3.25:8.24
1:3
C70-DAPr
85.16:2.73:8.21
1:3
C70-DAB
88.36:3.04:7.18
1:3
C70-DAPe 87.54:3.43:7.24 a sc: simple cubic lattice/lattice constant.
1:3
calcd for C76H24N6 89.40:2.37:8.23 calcd for C79H30N6 89.25:2.84:7.91 calcd for C82H36N6 89.11:3.28:7.60 calcd for C82H36N6 88.98:3.69:7.33
structurea
particle size/nm
sc/a = 10.43 A˚
200-500
sc/a = 10.54 A˚
200-600
sc/a = 10.61 A˚
200-1000
sc/a = 10.63 A˚
600-2000
Figure 4. FTIR spectra of C70-DAE. Figure 3. UV-vis-NIR spectra of (a) pristine C70, (b) C70-DAE, (c) C70-DAPr, (d) C70-DAB, and (d) C70-DAPe.
particle generation, a quite similar type of lattice structure, and almost the same molecular composition (C70/PAD). In general, C70- and C70n- (n = 2, 3, 4) show characteristic near-infrared (NIR) absorption near 1370 and 1170 nm, respectively.1,46,57 UV-vis-NIR spectra of as-prepared C70-PAD particles show broad absorption in the NIR region up to around 1500-1600 nm, as shown in Figure 3. For C70-DAE and C70-DAPr particles, broad peaks can be seen around 1100 nm, whereas C70-DAB and C70-DAPe have clearer peaks around 1150 and 1380 nm, respectively. We assume that the broad absorption band of C70-PAD particles near 1100-1150 nm is derived from multivalent anionic species of C70 (C702- and/or more highly reduced species) and that the peak at 1380 nm originates from C70-, formed as a result of electron transfer from PAD to C70.46,47 The presence of electronic interactions between C70 and PAD was further supported by EPR measurements where organic radical species were clearly observed in all cases (Figure S7). Further study is necessary to clarify the details of electronic interactions between C70 and PADs in microparticles. However, the results strongly suggest that the C70-PAD particles are made of donoracceptor complex species of C70 and PADs rather than the corresponding amination adducts. Figure 4 shows the FTIR spectra of C70-DAE. C70-DAE shows weak absorptions at 458, 531, 578, 675, and 795 cm-1 and relatively strong absorption at 1428 cm-1 assignable to parts of C70, where peaks at 531 and 1428 cm-1 are slightly shifted from pristine C70 (535 and 1430-1431 cm-1)58 and other peaks are almost unchanged. Absorptions at ∼1100, 1330, 1455, 15501580, 2862, 2917, and 3300-3400 cm-1 are attributed to C-N stretching, C-H symmetric deformation, C-H asymmetric deformation, N-H symmetric deformation, symmetric C-H (57) Wei, X.; Suo, Z.; Zhou, K.; Xu, Z.; Zhang, W.; Wang, P.; Shen, H. X.; Li J. Chem. Soc., Perkin Trans. 2 1999, 121. (58) Jishi, R. A.; Dresselhaus, M. S.; Dresselhaus, G.; Wang, K.-A.; Zhou, P.; Rao, A. M.; Eklund, P. C. Chem. Phys. Lett. 1993, 206, 187.
Langmuir 2010, 26(6), 4274–4280
stretching, asymmetric C-H stretching, and N-H stretching of DAE, respectively.59 The absence of aromatic C-H stretching bands, which typically appear at 3000-3100 cm-1, indicates that the inclusion of solvents (toluene/o-DCB) in the particles is negligibly small. A similar tendency was observed in other C70-PAD microparticles (Figure S8). Removal of PAD Molecules from the Microparticles in the Elucidation of the Microparticle Formation Mechanism. It is important to clarify the formation mechanism of C70-PAD rhombic dodecahedral particles and to understand the nature of the interaction between C70 and PAD. Two types of mechanisms should be taken into consideration in the present case. The first one is precipitate formation via the amination reaction between C70 and PADs, which promotes the aggregation of C70 adducts because of lowered solubility in the solution, as has been observed in some C60-aliphatic amine systems.27b,55,60 The second one is a donor-acceptor complexation between C70 and PADs possibly via electron-transfer (or charge-transfer) interaction, leading to the generation of precipitates. The complex species may be charged and thus favor aggregated states rather than freely dispersed states in nonpolar solvents (i.e., dielectric constant of the solvent (toluene/o-DCB = 85:15 v/v) used for the preparation of C70-PAD is estimated to be 3.5). Similar phenomena have been observed for cases such as the C60 (and higher fullerene)-1,8diazabicyclo[5.4.0]undec-7-ene system.61 As shown in Figure 3, C70-PAD particles have broad absorption bands in the NIR region up to around 1500-1600 nm. This strongly suggests the presence of electron-transfer (or chargetransfer) interactions between C70 and PAD in the C70-PADs particles. The results also suggest the presence of noncovalently bound PAD molecules in C70-PADs microparticles, which should (59) (a) Lakard, B.; Herlem, G.; Fahys, B. J. Chem. Phys. 2001, 115, 7219. (b) Choukourov, A.; Biederman, H.; Slavinska, I.; Trchova, M.; Hollander, A. J. Appl. Polym. Sci. 2004, 92, 979. (60) Matsuoka, K.; Seo, H.; Akiyama, T.; Yamada, S. Chem. Lett. 2007, 36, 934. (61) (a) Nagata, K.; Dejima, E.; Kikuchi, Y.; Hashiguchi, M. Chem. Lett. 2005, 34, 178. (b) Skiebe, A.; Hirsch, A.; Klos, H.; Gotschy, B. Chem. Phys. Lett. 1994, 220, 138.
DOI: 10.1021/la903355e
4277
Article
Matsuoka et al.
Table 2. Results of Elemental Analysis and the Structure of C70-PAD Microparticles after EtOH Rinsing
sample
elemental analysis after EtOH rinsing C/H/N
estimated composition C70/PAD
removed PAD/ mol %
C70-DAE 96.91:0.61:0.84 1:0.25 92 C70-DAPr 96.91:0.70:0.75 1:0.25 92 C70-DAB 95.64:0.71:0.83 1:0.25 92 C70-DAPe 93.42:1.02:1.62 1:0.5 83 a fcc: face-centered cubic lattice/lattice constant.
structurea fcc/a = 14.7 A˚ fcc/a = 14.7 A˚ fcc/a = 14.7 A˚ fcc/a = 14.7 A˚
Figure 6. XRD patterns of C70-PAD particles: (a) C70-DAE, (b) C70-DAPr, (c) C70-DAB, and (d) C70-DAPe after EtOH rinsing.
Figure 5. SEM images of (a) C70-DAE, (b) C70-DAPr, (c) C70-DAB,
Figure 7. UV-vis-NIR spectra of (a) C70-DAE, (b) C70-DAPr, (c) C70-DAB, and (d) C70-DAPe after rinsing with EtOH.
and (d) C70-DAPe after rinsing with EtOH.
be formed as a result of the donor-acceptor complexation of C70 and PAD in the liquid phase, followed by precipitation. It is also possible that the covalent bond formation and subsequent donor-acceptor complexation would induce precipitation. It is thus important to estimate how many PAD molecules are noncovalently accommodated in the C70-PAD microparticles to elucidate the formation mechanism. To verify this, we tried to remove noncovalently bound PAD molecules, if any, present in C70-PAD particles by rinsing the particles with appropriate solvents. We chose ethanol (EtOH) because EtOH is miscible with PAD but is a poor solvent for C70. C70-PAD particles (∼10 mg) were gently rinsed with EtOH (∼100 mL) to remove possibly unbound PAD molecules and dried in vacuo. As a result, PAD molecules were removed from the C70-PAD particles as confirmed from elemental analysis shown in Table 2. By comparing Tables 1 and 2, it is clear that the C70-PAD particles after EtOH rinsing showed significantly reduced compositions of H and N as compared to those without EtOH rinsing (Table 1). On the basis of the results of elemental analyses, it is estimated that about 80-90 mol % of the PAD molecules were removed by EtOH rinsing in all cases, indicating that at least 80-90 mol % of PAD molecules were noncovalently incorporated into C70-PAD particles. These results strongly suggest that the amination reaction hardly occurred during C70-PAD particle formation and that C70-PAD particles were mostly composed of donor-acceptor complex species between C70 and PADs. Additionally, it was somewhat surprising that the C70-PAD particles after EtOH rinsing completely maintained their initial shape, as verified by SEM observation (Figure 5). Besides the change in elemental composition, the original XRD patterns of C70-PAD particles completely disappeared after rinsing with EtOH. Alternatively, a new identical pattern appeared 4278 DOI: 10.1021/la903355e
Figure 8. FTIR spectra of (a) C70-DAE, (b) C70-DAPr, (c) C70DAB, and (d) C70-DAPe after rinsing with EtOH.
in all cases (Figure 6). This new pattern can be assigned to the face-centered cubic (fcc) lattice structure (a = 14.7 A˚) for pristine C70 as reported previously.62 These observations suggest that simple cubic frameworks of C70-PAD particles are sustained by the interaction between C70 and PADs and that they are collapsed upon removal of the PADs. Similar phenomena have been observed in the cases of C60/ferrocene nanosheets25b and an inclusion complex of C60 and p-benzylcalix[6]arene.26c In both cases, the resultant crystals remained almost unchanged but their crystal structures turned into pristine C60 upon the removal of guest molecules. Additionally, this type of phenomena resembles the characteristics of the first-generation type of porous coordination polymer compounds whose frameworks are sustainable (62) (a) Ramasesha, S. K.; Singh, A. K.; Seshadri, R.; Sood, A. K.; Rao, C. N. R. Chem. Phys. Lett. 1994, 220, 203. (b) Premila, M.; Sundar, C. S.; Sahu, P. C.; Bharathi, A.; Hariharan, Y.; Muthu, D. V. S.; Sood, A. K. Solid State Commun. 1997, 104, 237.
Langmuir 2010, 26(6), 4274–4280
Matsuoka et al.
Article
Figure 9. Proposed formation process of C70-PAD particles.
only when guest molecules are incorporated, but they show irreversible collapsing by the removal of guest molecules.63 Figure 7 shows the UV-vis-NIR spectra of C70-PAD after the removal of PAD molecules by EtOH rinsing. Broad NIR absorption bands almost completely disappeared and overall spectra became similar to that of pristine C70 (Figure 3a). The results clearly show that the NIR absorption bands come from electrontransfer (or charge-transfer) interactions between C70 and PAD molecules and that most of the PAD molecules were removed by EtOH rinsing. In addition, FTIR spectra of C70-PAD particles after rinsing with EtOH show several sharp peaks in the 400-2000 cm-1 region (458, 535, 565, 578, 642, 674, 795-796, 1133-1134, 14141416, and 1430-1431 cm-1 corresponding to the E10 and A200 modes of C70),58 as shown in Figure 8. Their relative intensities and peak positions are nearly identical to those of the pristine C70 sample, suggesting the C70-enriched character of microparticles after rinsing with EtOH. C-H and N-H stretching bands of the residual PAD species, possibly including a minority of covalently attached ones, are also observed. These results are well correlated with the results of elemental analysis, XRD measurements, and UV-vis-NIR spectra, demonstrating that C70-PAD particles are formed by the donor-acceptor complex species of C70 and PAD and that most of the PAD molecules can be removed from the corresponding particles by rinsing with EtOH. On the basis of the experimental findings, we propose the mechanism of the formation of C70-PAD particles as illustrated in Figure 9. First, one C70 molecule and three PAD molecules form donor-acceptor complex species most likely via electron-transfer (or charge-transfer) interactions in solution, as can be deduced from the results of elemental analysis, UV-vis-NIR spectra, and EPR spectra of the C70-PAD particles. Subsequently, the complex species immediately separate out from the liquid phase because of the reduction in solubility and then aggregate into simple cubic structures and grow into rhombic dodecahedral particles. EtOH (and possibly other appropriate solvents) can permeate the C70-PAD particles and can remove incorporated PAD molecules from the C70 frameworks. Accordingly, the simple cubic frameworks, sustained by the interaction between C70 and PAD, must be collapsed. (See the change from Figure 2 to Figure 6.) The resultant particles hold C70-enriched characters as clarified by UV-vis-NIR and FTIR spectra (Figures 7 and 8). It should also be noted that overall results show the capability of releasing the guest (PAD) molecules from C70-PAD particles. Exchange Reaction of PAD Molecules between Microparticles and the Bulk. From the above results, C70-PAD particles can be considered to be fullerene-based host-guest systems in which the C70 frameworks (hosts) accommodate PADs (guests) by electronic interaction between them. To investigate further the interaction between C70 and PAD in the particles, we (63) (a) Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed. 2004, 43, 2334. (b) Kitagawa, S.; Kondo, M. Bull. Chem. Soc. Jpn. 1998, 71, 1739.
Langmuir 2010, 26(6), 4274–4280
Figure 10. XRD patterns of (a) (A) C70-DAB, (B) C70-(DABfDAPr), (C) C70-(DABfDAE) and (b) their enlarged view near (100) diffraction. XRD patterns of (c) (D) C70-DAE, (E) C70-(DAEfDAPr), (F) C70-(DAEfDAPe) and (d) their enlarged view near (100) diffraction.
investigated the exchange behavior of incorporated PAD molecules in C70-PAD particles with different sizes of PAD molecules present in the bulk. The guest exchange reaction was carried out by immersing ∼10 mg of C70-PAD particles into 10 mL of a toluene/o-DCB (85:15 v/v) solution containing 1.0 10-2 mol of different PAD at room temperature for 5 min. No appreciable dissolution of C70-PAD particles was observed during the reaction time.64 The resultant particles were collected by vacuum filtration and dried in vacuo. Figure 10 shows the XRD patterns of the C70-DAB and C70-DAE particles before and after the exchange reaction with other amines. When C70-DAB particles were immersed in a solution of DAPr or DAE to carry out the exchange reaction (samples are denoted as C70-(DABfDAPr) and C70-(DABfDAE), respectively), diffraction peaks of the resultant samples shifted to wider angles while maintaining the original diffraction pattern (Figure 10B,C). Accordingly, the lattice constant was decreased from 10.61 to 10.54 and 10.43 A˚, respectively, and these values were nearly identical to those of C70-DAPR and C70-DAE (Table 1). On the contrary, when C70-DAE particles were immersed into the solution of DAPr or DAPe, diffraction peaks of the resultant samples denoted as C70-(DAEfDAPr) and C70-(DAEfDAPe) shifted to narrower angles without changing the original diffraction pattern (Figure 10E,F). Thus, the lattice (64) The concentration of PAD and the composition of solvent (toluene/o-DCB) in the PAD solution used for the guest-exchange reaction matched the exact conditions for C70-PAD preparation. Though it may not necessarily match every parameter, the coexistence of PAD and organic solvent should be required. C70-PAD particles were dissolved if they were in contact with neat PAD liquid.
DOI: 10.1021/la903355e
4279
Article
Figure 11. SEM images of (a) C70-(DABfDAPr), (b) C70-(DAB fDAE), (c) C70-(DAEfDAPr), and (d) C70-(DAEfDAPe).
Matsuoka et al.
particles. However, the corresponding bands of the CD2 group of DAE-d4 clearly appeared at 2212 and 2097 cm-1, respectively, and the intensities of the CH2 stretching bands seem to be decreased in the C70-(DABfDAE-d4) particles. This result further supports the presence of the guest exchange reaction. Under the experimental conditions of the above-described guest exchange reaction, the molar ratio of PAD incorporated into the initial C70-PAD particles to that of PAD present in the bulk solution is approximately 3:1000. The initially incorporated PAD molecules through electronic interaction with C70 would be gradually replaced with other PAD molecules present in the vicinity of the particle surface. Accordingly, all of the results clearly suggest that C70-PAD particles can undergo a guest molecule exchange reaction.
Conclusions
Figure 12. FTIR spectra of (a) C70-(DABfDAE-d4) and (b) C70-DAB.
constant increased from 10.43 to 10.55 or 10.60 A˚, respectively, and these values were close to those of C70-DAPr and C70-DAPe particles (Table 1). The morphologies of the resultant samples after the exchange reactions with other PAD molecules remained almost unchanged as shown in Figure 11. These results strongly suggest that PAD molecules initially accommodated in C70-PAD particles are exchanged at least to some extent and that the preorganized C70-PAD frameworks of the initial particles systematically shrink or expand to accommodate smaller (Figure 10B,C) or larger (Figure 10E,F) PAD molecules. We also attempted to exchange incorporated DAB molecules in the C70-DAB particles with deuterated DAE (DAE-d4) in the same manner. Figure 12 shows the difference in FTIR spectra between C70-DAB and C70-(DABfDAE-d4). Strong bands due to CH2 symmetric and asymmetric stretching of DAB molecules appear at 2927 and 2858 cm-1, respectively, in the C70-DAB
4280 DOI: 10.1021/la903355e
In summary, we have characterized the unique assembly behavior between C70 and PADs and the guest release/exchange capabilities of C70-PAD particles. First, C70 molecules were selectively assembled into rhombic dodecahedral particles through donor-acceptor complexation with PADs under carefully controlled conditions. Second, the C70-PAD particles acted as host-guest systems to release and exchange PAD molecules incorporated into the C70 framework, whereas the framework acted as a flexible cage in which to store PAD molecules without changing the apparent shape. Our findings are of substantial interest in basic science, especially with respect to the chemistry between fullerene and aliphatic amines and the new design of fullerene-based host materials. Acknowledgment. We thank associate professor Hiroaki Yonemura at Kyushu University for EPR measurements. XRD and FTIR measurements were made at the center of Advanced Instrumental Analysis, Kyushu University. This research was supported by research fellowships from the Japan Society for the Promotion of Science (JSPS) for young scientists (HAG1004391) and a Grant-in-Aid for Scientific Research of the Priority Area (area code 470) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. Supporting Information Available: Detailed studies of the effect of preparation conditions on C70-DAE microparticle formation; SEM and XRD analyses of the C70-1,2-DAPr assembly; EPR measurements of C70-PAD microparticles; and FTIR spectra of C70-DAPr, C70-DAB, and C70-DAPe. This material is available free of charge via the Internet at http://pubs.acs.org.
Langmuir 2010, 26(6), 4274–4280
