Cyanurate Binary Organogels Possessing Rigid

based on flexible dodecamethylene-tethered melamine dimers. ... azobenzene chromophores in the tether moiety upon forming well-defined nanofibers by ...
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Melamine-Barbiturate/Cyanurate Binary Organogels Possessing Rigid Azobenzene-Tether Moiety Shiki Yagai,* Takashi Karatsu, and Akihide Kitamura* Department of Applied Chemistry and Biotechnology, Faculty of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan Received July 29, 2005. In Final Form: August 27, 2005 Binary organogels were prepared from coaggregates of azobenzene-tethered melamine dimer and cyanurate/barbiturates. In the gels of hydrocarbon liquids, the coaggregates formed heavily entangled nanofibers, morphologies of which are dramatically different from the previously reported coaggregates based on flexible dodecamethylene-tethered melamine dimers. In the present systems, the rigidity of the azobenzene tether may induce regular packing of molecules. In addition, UV-vis and IR spectroscopic measurements provided unequivocal evidence for the contribution of the central amide groups and the azobenzene chromophores in the tether moiety upon forming well-defined nanofibers by hydrogen-bonding and face-to-face (H-type) π-π stacking interactions, respectively. As a result of tight molecular packing in the self-assembled nanofibers, the azobenzene moiety in the gel state showed remarkable resistance to trans f cis isomerization upon irradiation with UV light.

Introduction Formation of organogels by low molecular weight compounds is an attractive phenomenon arising from spontaneous formation of mesoscopically organized molecular self-assembly in the presence of solvent molecules.1 Cooperative formation of various weak noncovalent interactions eventually leads to the highly ordered nanostructures. Recent advances in the research field of low molecular weight gels include the functionalization of gelling compounds by introducing optically and electronically active chromophores, which can be applied to optoelectronic soft materials.2,3 In our approach toward the development of functional gels, we have used DAD‚ADA hydrogen-bonding interaction between melamine and cyanurate or barbiturate as primary intermolecular glue.4 On the basis of this type of noncovalent interaction, Hanabusa et al.5 reported the first two-component organogelators using linear tapelike aggregates of ditopic melamine and barbiturates as * To whom correspondence should be addressed: e-mail [email protected]. (1) (a) Terech, P.; Weiss, R. G. Chem. Rev. 1997, 97, 3133-3160. (b) Abdallah, D. J.; Weiss, R. G. Adv. Mater. 2000, 12, 1237-1247. (c) van Esch, J. H.; Feringa, B. L. Angew. Chem., Int. Ed. 2000, 39, 2263-2266. (2) Organogels containing π-conjugated chromophores: (a) Ajayaghosh, A.; George, S. J. J. Am. Chem. Soc. 2001, 123, 5148-5149. (b) Tamaru, S.-i.; Nakamura, M.; Takeuchi, M.; Shinkai, S. Org. Lett. 2001, 3, 3631-3634. (c) Yao, S.; Beginn, U.; Gress, T.; Lysetska, M.; Wu¨rthner, F. J. Am. Chem. Soc. 2004, 126, 8336-8348. (d) Sugiyasu, K.; Fujita, N.; Shinkai, S. Angew. Chem., Int. Ed. 2004, 43, 1229-1233. (e) An, B.-K.; Lee, D.-S.; Lee, J.-S.; Park, Y.-S.; Song, H.-S.; Park, S. Y. J. Am. Chem. Soc. 2004, 126, 10232-10233. (f) Kishimura, A.; Yamashita, T.; Aida, T. J. Am. Chem. Soc. 2005, 127, 179-183. (g) Ishi-i, T.; Hirayama, T.; Murakami, K.-i.; Tashiro, H.; Thiemann, T.; Kubo, K.; Mori, A.; Yamasaki, S.; Akao, T.; Tsuboyama, A.; Mukaide, T.; Ueno, K.; Mataka, S. Langmuir 2005, 21, 1261-1268. (h) Wu¨rthner, F.; Hanke, B.; Lysetska, M.; Lambright, G.; Harms, G. S. Org. Lett. 2005, 7, 967-970. (i) Engelkamp, H.; Middelbeek, S.; Nolte, R. J. M. Science 1999, 284, 785-788. (j) Messmore, B. W.; Hulvat, J. F.; Sone, E. D.; Stupp, S. I. J. Am. Chem. Soc. 2004, 126, 14452-14458. (k) Schoonbeek, F. S.; van Esch, J. H.; Wegewijs, B.; Rep, D. B. A.; de Haas, M. P.; Klapwijk, T. M.; Kellogg, R. M.; Feringa, B. L. Angew. Chem., Int. Ed. 1999, 38, 1393-1397. (l) Kawano, S.-i.; Fujita, N.; Shinkai, S. Chem.-Eur. J. 2005, 11, 4735-4742. (m) George, S. J.; Ajayaghosh, A.; Jonkheijm, P.; Schenning, A. P. H. J.; Meijer, E. W. Angew. Chem., Int. Ed. 2004, 43, 3422-3425. (n) George, S. J.; Ajayaghosh, A. Chem.-Eur. J. 2005, 11, 3217-3227.

extended supramolecular polymers required for gelation. On the other hand, our systems are based on flexible supramolecular polymers featuring dimeric melamine (bismelamine) tethered by flexible dodecamethylene linker (bisM, Figure 1),6 or cyclic aggregates (rosette) that can hierarchically stack into columnar aggregates.7 Practically, binary (two-component) organogel systems have a very intriguing advantage, that is, tunability in their structure and physical property of gels by just changing one of the two components.8 This aspect is emphasized by the recent works on the two-component dendritic organogels by Smith and co-workers.9 In our binary systems based on bismelamine, indeed, the macroscopic structure (3) Organogels containing photoresponsive chromophores: (a) Eastoe, J.; Sa´nchez-Dominguez, M.; Wyatt, P.; Heenan, R. K. Chem. Commun. 2004, 2608-2609. (b) de Jong, J. J. D.; Lucas, L. N.; Kellog, R. M.; van Esch, J. H.; Feringa, B. L. Science 2004, 304, 278-281. (c) de Jong, J. J. D.; Hania, P. R.; Pugzˇlys, A.; Lucas, L. N.; de Loos, M.; Kellog, R. M.; Feringa, B. L.; Duppen, K.; van Esch, J. H. Angew. Chem., Int. Ed. 2005, 44, 2373-2376. (d) Koumura, N.; Kudo, M.; Tamaoki, N. Langmuir 2004, 20, 9897-9900. (e) Murata, K.; Aoki, M.; Nishi, T.; Ikeda, A.; Shinkai, S. J. Chem. Soc., Chem. Commun. 1991, 1715-1718. (f) Murata, K.; Aoki, M.; Suzuki, T.; Harada, T.; Kawabata, H.; Komori, T.; Ohseto, F.; Ueda, K.; Shinkai, S. J. Am. Chem. Soc. 1994, 116, 6664-6676. (g) Ahmed, S. A.; Sallenave, X.; Fages, F.; Mieden-Gundert, G.; Mu¨ller, W. M.; Mu¨ller, U.; Vo¨gtle, F.; Pozzo, J.-L. Langmuir 2002, 18, 7096-7101. (h) Frkanec, L.; Jokic´, M.; Makarevic´, J.; Wolsperger, K.; ZÄ inic´, M. J. Am. Chem. Soc. 2002, 124, 9716-9717. (i) van der Laan, S.; Feringa, B. L.; Kellogg, R. M.; van Esch, J. Langmuir 2002, 18, 7136-7140. (i) Moriyama, M.; Mizoshita, N.; Yokota, T.; Kishimoto, K.; Kato, T. Adv. Mater. 2003, 15, 1335-1338. (k) Ayabe, M.; Kishida, T.; Fujita, N.; Sada, K.; Shinkai, S. Org. Biomol. Chem. 2003, 1, 2744-2747. (l) Inoue, D.; Suzuki, M.; Shirai, H.; Hanabusa, K. Bull. Chem. Soc. Jpn. 2005, 78, 721-726. (4) (a) Whitesides, G. M.; Simanek, E. E.; Mathias, J. P.; Seto, C. T.; Chin, D. N.; Mammen, M.; Gordon, D. M. Acc. Chem. Res. 1995, 28, 37-44. (b) Ariga, K.; Kunitake, T. Acc. Chem. Res. 1998, 31, 371-378. (c) Timmerman, P.; Prins, L. J. Eur. J. Org. Chem. 2001, 3191-3205. (d) Sherrington, D. C.; Taskinen, K. A. Chem. Soc. Rev. 2001, 30, 83-93 and references therein. (e) Lehn, J.-M. Polym. Int. 2002, 51, 825-839. (5) Hanabusa, K.; Miki, T.; Taguchi, Y.; Koyama, T.; Shirai, H. J. Chem. Soc., Chem. Commun. 1993, 1382-1384. (6) (a) Yagai, S.; Higashi, M.; Karatsu, T.; Kitamura, A. Chem. Mater. 2004, 16, 3582-3585. (b) Yagai, S.; Higashi, M.; Karatsu, T.; Kitamura, A. Chem. Mater. 2005, 17, 4392-4398. (7) (a) Yagai, S.; Karatsu, T.; Kitamura, A. Chem. Commun. 2003, 1844-1845. (b) Yagai, S.; Nakajima, T.; Karatsu, T.; Saitow, K.-i.; Kitamura, A. J. Am. Chem. Soc. 2004, 126, 11500-11508. (c) Yagai, S.; Nakajima, T.; Kishikawa, K.; Kohmoto, S.; Karatsu, T.; Kitamura, A. J. Am. Chem. Soc. 2005, 127, 11134-11139.

10.1021/la052076k CCC: $30.25 © 2005 American Chemical Society Published on Web 10/06/2005

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Figure 2. Possible noncovalent interactions for the aggregation of 1 with CA. Alkyl side chains are omitted for clarity. Scheme 1. Synthesis of 1a

bisM,6

Figure 1. Previously reported bismelamine azobenzene-tethered bismelamine 1, and complementary cyanurate CA and barbiturates B1 and B2.

and the rheological behavior of the gels are strongly dependent on the molecular structures of the cyanurate or barbiturate components.6b It has been established that the use of nonchromophoric cyanurate (CA in Figure 1) results in the formation of randomly coiled supramolecular polymers leading to the irregular fibrous aggregates, whereas the use of barbiturate-type dipolar merocyanines induces structural ordering of the randomly coiled supramolecular polymers, resulting in the formation of regular cylindrical fiber (B2) and two-dimensional sheet (B1) as a consequence of additional dipolar interaction between dyes. In the present study we attempt to induce structural ordering of our binary system by introducing a rigid azobenzene tether between the two melamine binding sites (1 in Figure 1). Introduction of the azobenzene moiety confers molecular rigidity required for regular molecular packing and may provides additional π-π stacking interactions enhancing interchain ordering of quasi-onedimensional supramolecular polymers connected by the (8) (a) Jeong, S. W.; Murata, K.; Shinkai, S. Supramol. Sci. 1996, 3, 83-86. (b) Inoue, K.; Ono, Y.; Kanekiyo, Y.; Ishi-I, T.; Yoshihara, K.; Shinkai, S. J. Org. Chem. 1999, 64, 2933-2937. (c) Singh, M.; Tan, G.; Agarwal, V.; Fritz, G.; Maskos, K.; Bose, A.; John, V.; McPherson, G. Langmuir 2004, 20, 7392-7398. (9) (a) Hirst, A. R.; Smith, D. K. Chem.-Eur. J. 2005, 11, 54965508. (b) Hirst, A. R.; Smith, D. K. Langmuir 2004, 20, 10851-10857. (c) Hirst, A. R.; Smith, D. K.; Feiters, M. C.; Geurts, H. P. M. Langmuir 2004, 20, 7070-7077. (d) Hirst, A. R.; Smith, D. K. Org. Biomol. Chem. 2004, 2, 2965-2971. (e) Huang, B.; Hirst, A. R.; Smith, D. K.; Castelletto, V.; Hamley, I. W. J. Am. Chem. Soc. 2005, 127, 7130-7139. (f) Hirst, A. R.; Smith, D. K.; Feiters, M. C.; Geurts, H. P. M. Chem.-Eur. J. 2004, 10, 5901-5910. (g) Hirst, A. R.; Smith, D. K.; Feiters, M. C.; Geurts, H. P. M.; Wright, A. C. J. Am. Chem. Soc. 2003, 125, 90109011. (h) Hardy, J. G.; Hirst, A. R.; Smith, D. K.; Brennan, C.; Ashworth, I. Chem. Commun. 2005, 385-387. (i) Partridge, K. S.; Smith, D. K.; Dykes, G. M.; McGrail, P. T. Chem. Commun. 2001, 319-320.

a (i) 2-Ethylhexylamine, THF, diisopropylethylamine (DIPEA), 0 °C, and then dioctylamine, DIPEA, rt; (ii) 30 equiv of 1,3-diaminopropane, DIPEA, THF, 90 °C; (iii) azobenzene-4,4′dicarbonyl chloride, toluene, rt.

DAD‚ADA triple hydrogen-bonding interaction (Figure 2). The two amide functionalities may also enhance the interchain association and ordering by hydrogen-bonding interaction. Results and Discussion Synthesis. Compound 1 was synthesized according to Scheme 1. Melamine 3 possessing 3-aminopropyl group was synthesized by the stepwise introduction of the appropriate amines into 1,3,5-trichlorotriazine at suitable reaction temperatures (see the footnote for Scheme 1).10 The reaction of 3 with azobenzene-4,4′-dicarbonyl chloride in toluene resulted in the precipitation of orange product, which was isolated and recrystallized from dimethyl sulfoxide (DMSO) to give pure compound 1. The characterization of 1 (100% trans isomer) was done by 1H NMR spectroscopy, fast atom bombardment mass spectrometry (FAB-MS), and elemental analysis. Gelation. While compound 1 did not form a gel in any organic liquids examined, the presence of 1 equiv of a complementary hydrogen-bonding component in Figure 1 leads to the gelation of several organic liquids when the mixture was dissolved in appropriate hot liquids and then cooled to ambient temperature. This clearly demonstrates the presence of complementary DAD‚ADA hydrogenbonding interactions. Table 1 summarizes the gelation behavior of the aggregates for several noncompeting solvents. Aromatic liquids were gelled by all the aggregates. This result is considerably different from the previous system based on bisM, in which benzene was gelled only by bisM‚CA and toluene was not gelled by bisM‚B2. It has been established that such a dramatic (10) Steffensen, M. B.; Simanek, E. E. Org. Lett. 2003, 5, 23592361.

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Table 1. Gelation Properties of the Binary Organogelators at 25 °Ca,b benzene toluene CH2Cl2 CHCl3 CCl4 cyclohexane hexane

1‚CA

1‚B1

1‚B2

G (0.35) G (0.27)c P S G (0.16)c PG I

G (0.40)c G(0.19)c P S G (0.15)c G (0.20)c I

PG PG PG S P P I

a Gelation test was carried out as previously reported.6a Gel phase was stable for at least 1 month. G, gel; PG, partial gel (mixture of gel and sol phases); S, soluble; P, precipitates; I, insoluble. b [Gelators] ) 5 mM. c For gels (G), the minimum gelation concentrations were also determined and are shown in parentheses (wt %).

Figure 3. Photographs of the benzene sol (60 °C) and gel (rt) of 1‚CA (1 mM).

dependence of the gelation ability on cyanurate/barbiturate component derives from the difference in the secondary structures (randomly coiled, folded, or self-assembled structure) of the flexible quasi-one-dimensional supramolecular polymers, determined by the dipolar interaction of cyanurate/barbiturate components. In the present system featuring the azobenzene tether in the supramolecular chain, therefore, effect of cyanurate/barbiturate components on gelation is weakened by the rigid nature of the main chains. In comparison with the previous system based on bisM, the present system shows remarkable enhancement in minimum gelation concentration and in gel-to-sol transition temperature when B1 was used as a complementary partner. Though the minimum gelation concentrations of 1‚B1 (0.19 wt %) and bisM‚B1 (0.25 wt %) in toluene do not show a significant difference, the gel-to-sol transition temperature of the resulting gel is significantly higher for 1‚B1 (63 °C) than for bisM‚B1 (38 °C). This clearly demonstrates that the gel network constructed by 1‚B1 is stronger than that of bisM‚B1 due to additional noncovalent interactions derived from the -NHCOazobenzene-CONH- tether moiety. Interestingly, upon gelation of toluene by 1‚CA, the pale yellow color of monomeric 1 observed in the sol state at 60 °C was strongly bleached (Figure 3), indicating the occurrence of electronic interaction between the azobenzene chromophores upon gelation. This aspect will be discussed later. To obtain insight into the nanoscale morphology of the gels, all the benzene gels were dried and observed by field emission scanning electron microscopy (FE-SEM). All the dried gels are strongly birefringent, indicating the presence of molecular anisotropy. Remarkably, all the xerogels showed finely entangled fibrous structures as shown in Figure 4. A high-magnification image for 1‚B1 (Figure 4C) revealed that each fiber is composed of several thin

Figure 4. FE-SEM images of the dried benzene gels of 1‚CA (A), 1‚B1 (B, 15000×, and C, 43000×), and 1‚B2 (D).

fibers with an average diameter of ca. 50 nm. Such fibrous morphologies of the self-organized aggregates is dramatically different from those of the previously reported binary organogels based on the coaggregates of flexible dodecamethylene-tethered bisM with CA (irregular fiber),6a B1 (cylindrical fiber), or B2 (sheet).6b Formation of the well-

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Figure 6. UV-vis spectra of 1 (50 µM) in toluene in the absence (dotted line) and presence (solid line) of 1 equiv of CA.

Figure 5. IR spectra of 1 in chloroform (10 mM, dashed line) and a dried gel of 1‚CA (solid line). The broad band at around 1700 cm-1 in the gel is derived from the imide carbonyl group of CA.

defined fibers, which is independent of the molecular structures and the physical properties of the diimide components, may partly originate from the rigid nature of azobenzene-tethered bismelamine 1. In addition, the hydrogen-bonding interaction of the two amide groups and π-π stacking interaction between the azobenzene chromophores, which enable interchain ordering of quasione-dimensional supramolecular polymers, might contribute to the formation of regular fibrous structures. Contribution of the amide groups to the formation of well-defined fibrous structure was confirmed by IR spectroscopy. Compound 1 alone dissolved in chloroform exhibited IR bands corresponding to CdO and N-H stretchings of the free amide groups at 1653 and 3447 cm-1, respectively (dashed line in Figure 5). In the dried gel of 1‚CA, the former band shifted to 1630 cm-1 and the latter band completely disappeared from the original position (solid line in Figure 5). It can be assumed that the latter band is embedded in a broad band at around 3310 cm-1 involving the NH stretching band of CA. These results clearly show the hydrogen-bonding interaction of the amide group of 1 upon gelation. Orthogonal formation of the DAD‚ADA and amide-amide hydrogen bonds as shown in Figure 2 is ambiguous at this stage; however, the following UV-vis study strongly suggests the presence of amide-amide hydrogen-bonding interactions. Supramolecular Polymerization in Diluted Solution. To examine the possibility of the π-π stacking interaction between the azobenzene chromophores in the self-assembled fibers, we next examined the supramolecular polymerization by UV-vis spectroscopy. For this purpose, cyanurate CA was selected as a complementary

partner for 1 because it is transparent in the absorption region of the azobenzene moiety. Dynamic light scattering (DLS) measurement revealed that the equivalent molar mixture of 1 and CA in toluene at a concentration of 50 µM affords soluble aggregates with an average hydrodynamic diameter exceeding 500 nm, indicating the high polymerization ability of these building blocks. Allowing the solution to stand for several hours resulted in the formation of very large aggregates with an average hydrodynamic diameter exceeding the limitation of our DLS apparatus (1000 nm). Therefore, freshly prepared solution was used for UV-vis measurements to avoid a concentration change of soluble components as well as scattering of light. As shown in Figure 6, λmax of the π-π* band of monomeric 1 dissolved in toluene at 330 nm hypsochromically shifted to 310 nm in the presence of CA. In addition, the n-π* band at 450 nm is strongly bleached, which may cause gelation-induced bleaching as shown in Figure 3. The former spectral change is unequivocal evidence for the face-to-face stacking interaction (Haggregation) of the azobenzene chromophores.11,12 Such a face-to-face stacking interaction ensures close proximity of the amide groups between the DAD‚ADA quasi-onedimensional supramolecular polymer chains. This is in good agreement with the hydrogen-bonding interaction between the amide groups as inferred from the IR study. Therefore, the aggregation motif shown in Figure 2 is strongly suggested for the present organogel system. Azobenzene derivatives are known to show remarkable resistance against trans f cis photoisomerization when they form H-type aggregates.12a-c Therefore we investigated whether the azobenzene moiety of 1 can photoisomerize in the presence of CA. The irradiation of monomeric 1 (100% trans isomer) in toluene at around 330 nm resulted in trans f cis isomerization of azobenzene (11) Kasha, M.; Rawls, H. R.; Bayoumi, E. I. A. Pure Appl. Chem. 1965, 11, 371-392. (12) (a) Song, X.; Perlstein, J.; Whitten, D. G. J. Am. Chem. Soc. 1995, 117, 7816-7817. (b) Kawasaki, T.; Tokuhiro, M.; Kimizuka, N.; Kunitake, T. J. Am. Chem. Soc. 2001, 123, 6792-6800. (c) Shimomura, M.; Kunitake, T. J. Am. Chem. Soc. 1987, 109, 5175-5183. (d) Song, X.; Perlstein, J.; Whitten, D. G. J. Am. Chem. Soc. 1997, 119, 91449159. (e) Kobayashi, H.; Koumoto, K.; Jung, J. H.; Shinkai, S. J. Chem. Soc., Perkin Trans. 2 2002, 1930-1936. (f) Murata, K.; Aoki, M.; Suzuki, T.; Harada, T.; Kawabata, H.; Komori, T.; Ohseto, F.; Ueda, K.; Shinkai, S. J. Am. Chem. Soc. 1994, 116, 6664-6676. (g) Kobayashi, H.; Friggeri, A.; Koumoto, K.; Amaike, M.; Shinkai, S.; Reinhoudt, D. N. Org. Lett. 2002, 4, 1423-1426.

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now preparing such aggregates with electronically active dye molecules. Experimental Section 1H

Figure 7. UV-vis spectral changes of 1 (50 µM) in toluene upon irradiation with 335-nm light (0, 5, and 20 min).

moieties as demonstrated by the clear UV-vis spectral changes shown in Figure 7. A photostationary state was obtained by the 1-h irradiation, giving a trans:cis ratio of ca. 50:50. Irradiation of the UV-irradiated solution with 450-nm light resulted in complete loss of the cis isomer within 5 min. Thus, monomeric 1 shows reversible photoisomerization. In sharp contrast, the aggregates 1‚CA in toluene did not show UV-vis spectral changes upon prolonged irradiation with UV light, indicating the aggregationinduced suppression of the isomerization. This result clearly shows that the azobenzene chromophore of 1 is tightly packed in highly organized self-assembled nanostructures. Conclusion We have reported binary organogelators based on coaggregates of the azobenzene-tethered bismelamine and cyanurate or barbiturates. Complementary DAD‚ADA triple hydrogen bonding, amide-amide hydrogen bonding, and π-π stacking interactions between the azobenzene chromophores cooperatively promote the aggregation of these supramolecular building blocks, leading to the formation of well-defined nanofibers. The present study demonstrates that our bismelamine compound is a versatile scaffold for creating functional nanostructures comprising highly organized chromophoric aggregates when appropriate dye molecules can be covalently introduced into the tether moiety as in 1. Therefore, many optically13 or electronically14 active self-assemblies can be created from bismelamine/diimide aggregates. We are

General. NMR spectra were recorded on JEOL LA400 and LA500 spectrometers. Electron microscopic observation was carried out by JEOL JSM-6330F field emission scanning electron microscopy. The dried gels were sputtered with Au. The solvents for the spectroscopic measurements and the gelling experiments were all spectral-grade. Dynamic light scattering measurements were conducted on a Beckmann Coulter N5 particle analyzer. The hot sample solutions were filtered with Millipore membrane filter (pore size ) 0.2 µm) before measurements to remove dust. Photoirradiation experiments were performed on a fluorometer equipped with a 150 W xenon lamp (20 nm excitation bandwidth). Compound 2 was prepared by previously reported procedures.6a Preparation of the Xerogels. The gels in appropriate vials were immersed in liquid N2 for a few seconds. The samples were then dried overnight under vacuum. Synthesis of Compound 1. A tetrahydrofuran (THF) solution (30 mL) of compound 2 (2.0 g, 4.15 mmol) and an excess amount (9.2 g, 125 mmol) of 1,3-diaminopropane was heated at 90 °C for 12 h under N2 atmosphere. The mixture was poured into water and extracted with ethyl acetate. The organic layer was washed with water and dried over Na2SO4, and the solvent was evaporated. The residue was purified by silica gel column chromatography (eluted with NH4OH/MeOH/CH2Cl2 ) 2/8/90) to give compound 3 as a transparent oil. 1H NMR (400 MHz, CDCl3) δ ) 4.82 (br s, 1H), 4.68 (br s, 1H), 3.44 (m, 6H), 3.29 (m, 2H), 2.77 (t, J ) 7 Hz, 2H), 1.67 (m, 2H), 1.20-1.60 (m, 35H), 0.89 (m, 12H); MS (FAB) 544 (M+). To a dry toluene solution (30 mL) of compound 3 (1.16 g, 2.23 mmol) containing 1 mL of triethylamine, azobenzene-4,4′dicarbonyl chloride (0.3 g, 0.98 mmol) in toluene (20 mL) was slowly added under N2 atmosphere at room temperature. After the reaction mixture was stirred for 2 h, the precipitated product was filtered and washed with toluene and then with water repeatedly. The residual solid was purified by silica gel column chromatography (eluted with MeOH/CH2Cl2 ) 15/85) and recrystallized from dimethyl sulfoxide to give compound 1 as a pink powder. 1H NMR (500 MHz, CDCl3) δ ) 8.62 (t, J ) 4 Hz, 2H), 8.06 (d, J ) 9 Hz, 4H), 7.97 (d, J ) 9 Hz, 4H), 6.50 (br s, 2H), 6.40 (br s, 2H), 3.20-3.50 (m, 16H), 3.05-3.15 (m, 4H), 1.70-1.90 (m, 4H), 1.40-1.60 (m, 10H), 1.10-1.40 (m, 56H), 0.70-0.90 (m, 24H); MS (FAB) 1274 (M+). Anal. Calcd for C74H128N16O2: C, 69.77; H, 10.13; N, 17.59; O, 2.51. Found: C, 69.44; H, 10.01; N, 17.82.

Acknowledgment. This research was partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Young Scientists (B) (17750120). S.Y. thanks The Kao Foundation For Arts And Sciences. LA052076K (13) (a) Yagai, S.; Karatsu, T.; Kitamura, A. Chem.-Eur. J. 2005, 11, 4054-4063. (b) Hecht, S. Small 2005, 1, 26-29. (14) Reviews: (a) Hoeben, F. J. M.; Jonkheijm, P.; Meijer, E. W.; Schenning, A. P. H. J. Chem. Rev. 2005, 105, 1491-1546. (b) Schenning, A. P. H. J.; Meijer, E. W. Chem. Commun. 2005, 3245-3258.