© Copyright 2006 American Chemical Society
FEBRUARY 28, 2006 VOLUME 22, NUMBER 5
Letters Fluorescence from Aromatic Compounds Isolated in the Solid State by Double Intercalation Using Layered Polymer Crystals as the Host Solid Shinya Oshita and Akikazu Matsumoto* Department of Applied Chemistry, Graduate School of Engineering, Osaka City UniVersity, Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan ReceiVed December 24, 2005 Poly(muconic acid)s, stereoregular polymer crystals obtained by topochemical polymerization using supramolecular control, function as the layered host solids for organic intercalation, in which alkylamines as the guest species are reversibly inserted into them through an acid-base interaction. We now report a double-intercalation method using alkylamine and pyrene as the guests to control the fluorescence property in the solid state. An aromatic compound can be separately introduced into the hydrophobic layers of the ammonium polymer crystals. The aromatic molecules, which are sandwiched between two alkyl layers, show fluorescence emission from the single molecule but not the excimer. This method can be applied to various organic photofunctional materials showing unique fluorescence properties.
Introduction A significant number of photofunctional materials based on their fluorescence properties have been developed using heterogeneous systems such as polymer composites,1 organic crystals,2 organic-inorganic hybrids,3 intercalation compounds,4 and supramolecular materials.5 In particular, supramolecular chemistry has become increasingly important for obtaining the desired structure by a combination of coordination bonding, * Corresponding author. E-mail:
[email protected] Phone: +81-6-6605-2981. Fax: +81-6-6605-2981. (1) (a) Lee, J.; Sundar, V. C.; Heine, J. R.; Bawendi, M. G.; Jensen, K. F. AdV. Mater. 2000, 12, 1102. (b) Marsitzky, D.; Vestberg, R.; Blainey, P.; Tang, B. T.; Hawker, C. J.; Carter, K. R. J. Am. Chem. Soc. 2001, 123, 6965. (2) (a) Mizobe, Y.; Tohonai, N.; Miyata, M.; Hasegawa, Y. Chem. Commun. 2005, 1839. (b) Mutai, T.; Satou, H.; Araki, K. Nat. Mater. 2005, 4, 685. (c) Fei, Z.; Kocher, N.; Mohrschladt, C. J.; Ihmels, H.; Stalke, D. Angew. Chem., Int. Ed. 2003, 42, 783. (d) Irie, M.; Fukaminato, T.; Sasaki, T.; Tamai, N.; Kawai, T. Nature 2002, 420, 759. (3) (a) Coe, S.; Woo, S. K.; Bawendi, M.; Buloviæ, V. Nature 2002, 420, 800. (b) O’Connell, M. J.; Bachilo, S. M.; Huffman, C. B.; Moore, V. C.; Strano, M. S.; Haroz, E. H.; Rialon, K. L.; Boul, P. J.; Noon, W. H.; Kittrell, C.; Ma, J.; Hauge, R. H.; Weisman, R. B.; Smalley, R. E. Science 2002, 297, 593. (c) Lu, X.; Manners, I.; Winnik, M. A. Macromolecules 2001, 34, 1917. (4) Ogawa, M.; Kuroda, K. Chem. ReV. 1995, 95, 399.
hydrogen bonding, van der Waals interaction, and other weak intermolecular interactions. Poly(muconic acid)s, stereoregular polymer crystals obtained by topochemical polymerization using supramolecular control, function as the layered host solids for organic intercalation in which alkylamines as the guest species are reversibly inserted into them through an acid-base interaction.6,7 The layered host polymer crystals are obtained by the topochemical polymerization of alkylammonium muconate as the 1,3-diene dicarboxylic acid monomer under photoirradiation in the crystalline state.8 In general, a host compound recognizes molecules or ions and reversibly accepts them during the intercalation reaction.9 (5) (a) Dalgarno, S. J.; Tucker, S. A.; Bassil, D. B.; Atwood, J. L. Science 2005, 309, 2037. (b) Papaefstathiou, G. S.; Zhong, Z.; Geng, L.; MacGillivray, L. R. J. Am. Chem. Soc. 2004, 126, 9158. (c) Schmelz, O.; Mews, A.; Basche´, T.; Herrmann, A.; Mu¨llen, K. Langmuir 2001, 17, 2861. (6) Matsumoto, A.; Odani, T.; Sada, K.; Miyata, M.; Tashiro, K. Nature 2000, 405, 328. (7) Matsumoto, A.; Oshita, S.; Fujioka, D. J. Am. Chem. Soc. 2002, 124, 13749. (8) (a) Matsumoto, A. Polym. J. 2003, 35, 93. (b) Matsumoto, A. Top. Curr. Chem. 2005, 254, 263.
10.1021/la053481e CCC: $33.50 © 2006 American Chemical Society Published on Web 02/01/2006
1944 Langmuir, Vol. 22, No. 5, 2006
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Consequently, the guest species are aligned in a 2D interlayer space. If the guest molecules strongly interact with a layered host solid through ionic, hydrogen, or coordination bond formation, then we can strictly control the position and conformation of the guests. Actually, however, a limited number of examples have been reported as the layered host assembly, constructed only with organic compounds on the basis of supramolecular architecture, leading to successful intercalation reactions.10 This is due to the difficulty of maintaining a layered structure during repeated reactions when an organic sheet consists of noncovalent bonds between the low-molecular-weight compounds. In contrast, the lamellar structure of an inorganic host, such as graphite, is structurally robust because of covalent bonds in the lamellar plane. The organic polymer crystals also have a robust layer structure. They are suitable as host materials for multistep intercalations. We now report a double-intercalation method using alkylamine and pyrene as guests to control the fluorescence property in the solid state.
Results and Discussion We synthesized plate crystals of poly(muconic acid) (PMA) as host compounds via the solid-state polymerization of di(benzylammonium) muconate and the subsequent solid-state hydrolysis. Dodecylamine (DD) was intercalated into the obtained PMA via an acid-base reaction7 (Figure 1a). A polymer sheet is sandwiched between two guest layers to make a BAB-type stacking unit, where A and B refer to the acid and base layers, respectively. The PMA intercalated with DD (PMA/DD) was further dispersed into a diethyl ether solution containing pyrene (Py) (ca. 0.15 mol/L) to conduct the second-step intercalation. A change in the morphology was observed by microphotoscopy during the intercalation reaction. The first-step intercalation was detected by a drastic change in crystal size along a particular direction (d ) 32.4 Å for PMA/DD). In the second-step intercalation, the structural change was small, but its fluorescence emission suggested the incorporation of Py molecules. After second-step intercalation, we confirmed an increase of 4 Å in the d value, which corresponds to the molecular thickness of Py, using wide-angle X-ray diffraction (d ) 36.4 Å for PMA/DD/ Py) (Figure 2a). When poly[di(dodecylammonium) muconate] (PDDMA), obtained from the corresponding monomer crystals by solid-state polymerzation,7 was used for the second-step intercalation, a change in the interlayer space during the intercalation was more clearly observed because of their higher crystallinity11 (Figure 2b). The change in the d value suggests that the Py molecules lie parallel to the layer of the host polymers. The driving force for the second-step intercalation is the hydrophobic and CH-π interactions between the alkyl layer and Py molecules. A wide range of solvents such as diethyl ether, tetrahydrofuran, acetone, hexane, and toluene were available as the dispersant for the second-step intercalation. This supports the fact that the combination of the CH-π interaction is effective for the intercalation of Py in addition to the hydrophobic (9) ComprehensiVe Supramolecular Chemistry, Solid-State Supramolecular Chemistry: Two- and Three-Dimensional Inorganic Networks; Atwood, J. L., Davies, J. E. D., MacNicol, D. D., Vo¨gtle, F., Eds.; Pergamon: Oxford, England, 1996; Vol. 7. (10) (a) Nakano, K.; Sada, K.; Nakagawa, K.; Aburaya, K.; Yoswathananont, N.; Tohnai, N.; Miyata, M. Chem.sEur. J. 2005, 11, 1725. (b) Atwood, J. L.; Barbour, L. J.; Jerga, A.; Schottel, B. L. Science 2002, 298, 1000. (c) Holman, K. T.; Pivovar, A. M.; Swift, J. A.; Ward, M. D. Acc. Chem. Res. 2001, 34, 107. (d) Biradha, K.; Dennis, D.; MacKinnon, V. A.; Sharma, C. V. K.; Zaworotko, M. J. J. Am. Chem. Soc. 1998, 120, 11894. (11) PDDMA has a chemical structure identical to that of PMA/DD except for its crystallinity. The crystallinity of these polymer crystals was compared by X-ray analysis and Raman spectroscopy. See Oshita, S.; Matsumoto, A. Chem.s Eur. J., in press.
Figure 1. (a) Double intercalation of alkylamine and Py as guests into PMA as the host. PMA/DD with a BAB-type stacking structure was further intercalated with Py molecules by hydrophobic and CH-π interactions. The compounds obtained after the double intercalations (PMA/DD/Py) showed blue fluorescence emission under UV irradiation at 365 nm. (b) Conventional intercalation of (1-pyrenyl)methylamine (PyCH2NH2) into PMA. The pyrene moieties incorporated into the space between the alkyl layers of the polymer crystals showed green fluorescence emission from an excimer under 365 nm excitation.
Figure 2. Change in wide-angle X-ray diffraction profiles and fluorescence emission spectra for the intercalation of aromatic molecules into PMA/DD and PDDMA. (a) PMA/DD (blue, d ) 32.4 Å) and PMA/DD/Py (red, d ) 36.4 Å); (b) PDDMA (blue, d ) 32.0 Å) and PDDMA intercalated with Py (red, d ) 32.0 and 36.5 Å).
interaction. This is the first example of a multistep intercalation or inclusion in organic systems, whereas similar multistep inorganic intercalation systems are ubiquitous.4,12 The role of the crystalline polymer sheet of the host is proved by the following experimental result; no triple-layer crystal was formed by direct crystallization from a solution including muconic acid, DD, and Py. (12) Significant examples of multistep intercalations have been reported in inorganic layered host solids. See, as a recent example, Okada, T.; Watanabe, Y.; Ogawa M. Chem. Commun. 2004, 320.
Letters
Figure 3. Fluorescence emission spectra of Py in methanol (3 × 10-5 mol/L) (black, λmax ) 393 nm), Py in the solid state (blue, λmax ) 448 nm), PMA/DD/Py in the solid state (red, λmax ) 393 nm), and PMA intercalated with (1-pyrenyl)methylamine by our previous method using an acid-base reaction (green, λmax ) 475 nm). The excitation wavelength was 350 nm in all cases.
The doubly intercalated polymer crystals showed a monomer emission from Py similar to the emission from its dilute solution, whereas no excimer emission was observed around 460 nm (Figure 3). In general, the intensity of the excimer emission increases with an increase in the concentration of Py in solution (>10-6 mol/L) or in organized media such as a polymer matrix, Langmuir-Blodgett films, micelles, and silica gel.13 In the crystalline state or matrix at high Py concentration, Py molecules form a dimer with a face-to-face arrangement.14 In the case of the inorganic intercalation, Py tends to form a similar excimer state.15 When Py is incorporated into polymer crystals by the previous organic intercalation approach,16 that is, the PMA crystals react with (1-pyrenyl)methylamine, it provides the intercalated polymer crystals with excimer emissions due to the face-to-face interaction between the Py moieties of the guest amine (Figure 1b and green spectrum in Figure 3). The fluorescence property as a result of monomer emission is based on the unique structure of Py in the intercalation compounds PMA/DD/Py; pyrene molecules are lying parallel to the host layers, and they have no interactions with each other. Fluorescence emission for the single molecule was independent of the reaction conditions for the second-step intercalation such as the Py concentration in solution and the reaction time. We also succeeded in the double intercalation with other aromatic molecules, such as anthracene, carbazole, naphthalene, and perylene, using a similar method (Figure 4). Eventually, the enlargement of the interlayer spacing is the same for all of the intercalations. All of the aromatic compounds intercalated with the same structure are lying parallel to the layer in the hydrophobic space. Thus, we have demonstrated the multistep incorporation of aromatic guests into organic crystals by a double intercalation using PMA as the host. We have developed a double-intercalation system using poly(muconic acid) as the layered host solids. During this (13) (a) Winnik, F. M. Chem. ReV. 1993, 93, 587. (b) Parker, C. A.; Hatchard, C. G. Trans. Faraday Soc. 1963, 59, 284. (c) Johnson, G. E. Macromolecules 1980, 13, 839. (d) Yamazaki, I.; Tamai, N.; Yamazaki, T. J. Phys. Chem. 1987, 91, 3572. (e) Cao, T.; Munk, P.; Ramireddy, C.; Tuzarlt Z.; Webber, S. E. Macromolecules 1991, 24, 6300. (f) Bauer, R. K.; Borenstein, R.; Mayo, P. D.; Okada, K.; Rafalska, M.; Ware, W. R.; Wu, K. C. J. Am. Chem. Soc. 1982, 104, 4635. (14) Robertson, J. M.; White, J. G. J. Chem. Soc. 1947, 358. (15) DellaGuardla, R. A.; Thomas, J. K. J. Phys. Chem. 1983, 87, 3550. (16) Odani, T.; Matsumoto, A. Polym. J. 2002, 34, 841.
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Figure 4. Change in wide-angle X-ray diffraction profiles of the second-step intercalation of aromatic molecules into PDDMA. PDDMA before intercalation (black, d ) 32.0 Å) as well as PDDMA intercalated with Py (red, d ) 32.0 and 36.5 Å), anthracene (blue, d ) 32.0 and 36.5 Å), and carbazole (green, d ) 32.0 and 36.5 Å).
intercalation, alkylamines and aromatic compounds as the guest species are reversibly inserted into the polymer crystals. An aromatic compound can be separately introduced into the hydrophobic layers of the ammonium polymer crystals. The aromatic molecules, which are sandwiched between two alkyl layers, show fluorescence emission from the single molecule but not the excimer. This method can be applied to various organic photofunctional materials showing unique fluorescence properties. Experimental Section (Z,Z)-Muconic acid was supplied from Mitsubishi Chemical Co., Ltd, Tokyo. (1-Pyrenyl)methylamine was purchased as the hydrochloric salt from Aldrich Chemical Co., Inc. and used after neutralization. The other commercial chemicals were used as received without further purification. Di(dodecylammonium) (Z,Z)-muconate was prepared from (Z,Z)-muconic acid and dodecylamine (DD) in methanol and was quantitatively isolated by precipitation in a large amount of diethyl ether, followed by recrystallization from methanol. The photopolymerization of di(dodecylammonium) (Z,Z)-muconate was carried out in the crystalline state under UV irradiation using a high-pressure mercury lamp (Toshiba SHL-100-2, 100 W) at a distance of 10 cm. The resulting polymer was isolated by removing the unreacted monomer with methanol. Poly[di(dodecylammonium) (Z,Z)-muconate] (PDDMA) was quantitatively hydrolyzed by stirring in aqueous methanol containing 1 M HCl for 1 h at room temperature, resulting in poly(muconic acid) (PMA). The procedure for the second-step intercalation was as follows. The PMA/DD and PDDMA crystals (25 mg) were dispersed in a diethyl ether solution (10 mL) containing dissolved pyrene and stirred at room temperature for 2 h. The polymer crystals were isolated with a Millipore filter (0.1 µm), washed with a small amount of fresh diethyl ether (ca. 10 mL), and dried in vacuo. The preparation of the host compounds and first-step intercalation were carried out according to the methods described in a previous paper.7 Wide-angle X-ray diffraction was recorded using a RINT-Ultima 2100 diffractometer with Cu KR radiation (λ ) 1.5418 Å). The fluorescence emission spectra were collected at ambient temperature using a JASCO FP-6600 spectrometer.
Acknowledgment. This work was supported by a Grantin-Aid for Scientific Research in Priority Area “Molecular Nano Dynamics (432)” (no. 160722) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. LA053481E
