Formation of Helical J-Aggregate of Chiral Thioether-Derivatized

A chiral thioether-substituted phthalocyanine ((2,3,9,10,16,17,23 ... In certain cases, biological supramolecules exhibit a distinct helical or twiste...
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Langmuir 2006, 22, 1630-1639

Formation of Helical J-Aggregate of Chiral Thioether-Derivatized Phthalocyanine Bound by Palladium(II) at the Toluene/Water Interface Kenta Adachi,† Kenji Chayama,‡ and Hitoshi Watarai*,† Department of Chemistry, Graduate School of Science, Osaka UniVersity, Toyonaka, Osaka, 560-0043, Japan, and Department of Chemistry, Faculty of Science and Engineering, Konan UniVersity, Kobe, Hyogo, 658-0072, Japan ReceiVed September 26, 2005. In Final Form: December 5, 2005 A chiral thioether-substituted phthalocyanine ((2,3,9,10,16,17,23,24-octakis-1-phenylethylthiophthalocyaninato)magnesium(II) [MgPc(SEtPh)8]) has been synthesized, which can be bound by soft-metal ions such as palladium(II) ion. Aggregates formed from MgPc(SEtPh)8 and Pd(II) in toluene and at the toluene/water interface were characterized by means of UV-vis absorption and circular dichroism (CD) spectrometries using centrifugal liquid-membrane (CLM) cell. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF/MS) and scanning electron microscope (SEM) were used as complementary techniques. The toluene solution of MgPc(SEtPh)8 had no optical chirality. However, the addition of PdCl2 into the toluene solution of MgPc(SEtPh)8 induced optical chirality, which indicated the formation of a twisted H-type dimer (face-to-face fashion) of MgPc(SEtPh)8 bound by four PdCl2 in the bulk toluene solution. On the other hand, in the toluene/water interface, helical J-aggregate (headto-tail fashion) of MgPc(SEtPh)8 bound by PdCl2 was formed, in which one J-aggregate unit contained five 1:2 complexes of MgPc(SEtPh)8-Pd(II) on average. On the basis of the experimental results and the exciton theory for optical chirality, a possible mechanism for the chiral aggregation of MgPc(SEtPh)8-Pd(II) complexes at the interface was proposed. In the present study, we demonstrated a novel strategy for the design of helical phthalocyanine aggregates using the liquid/liquid interface as a template.

1. Introduction The organization of molecular components through supramolecular assembly is a very useful technique to obtain species with well-defined properties and morphology.1-3 Recently, the importance of molecular chirality in the case of self-assembled materials has been extensively recognized. In living organisms, optically active macromolecules, such as proteins, nucleic acids, and polysaccharides, are universally involved in the life processes.4,5 These macromolecules possess specific conformational and highly ordered structure associated with their chiral properties. In certain cases, biological supramolecules exhibit a distinct helical or twisted structure, which is a very conspicuous sign of the optical chirality of the supramolecular aggregate.6-8 The spontaneous self-assembly of molecules into supramolecular structures is the result of various noncovalent interactions such as hydrogen binding, electrostatic, dipole-dipole, and van der Waals interactions. A variety of artificial self-assembled chiral structures comprising helical fiber and twisted ribbons of sugars,9 helicenes,10 helical metal complexes,11-13 or block copolymers14-16 * Corresponding author. E-mail: [email protected]. † Osaka University. ‡ Konan University. (1) Lehn, J. M. Supramolecular Chemistry: Concepts and PerspectiVes; WileyVCH: Weinheim, Germany, 1995. (2) Steed, J. W.; Atwood, J. L. Supramolecular Chemistry; John Wiley & Sons: New York, 2000. (3) Reinhoudt, D. N., Ed. Supramolecular Materials and Technologies; John Wiley & Sons: New York, 1999. (4) Watson, J. D.; Crick, F. H. C. Nature 1953, 171, 737. (5) Straley, J. P. Phys. ReV. A 1976, 14, 1835. (6) Engelman, D. M.; Steitz, T. A. Cell 1981, 23, 411. (7) Eisenberg, D.; Weiss, R. M.; Terwilliger, T. C. Nature 1982, 299, 371. (8) Hildebrand, P. W.; Rother, K.; Goede, A.; Preissner, R.; Fro¨mmel, C. Biophys. J. 2005, 88, 1970. (9) Fuhrhop, J.-H.; Helfrich, W. Chem. ReV. 1993, 93, 1565. (10) Nuckolls, C.; Katz, T. J.; Verbiest, T.; Elshocht, S. V.; Kuball, H.-G.; Kiesewalter, S.; Lovinger, A. J.; Persoons, A. J. Am. Chem. Soc. 1998, 120, 8656.

have been created from chiral molecules employing noncovalent interactions described above. Phthalocyanine (Pc) compounds, which are structural analogues of porphyrins (Pr), are the subject of intense research activity due to their useful catalytic, optical, and chemical sensing properties.17 In recent years, Pc and Pr self-assembled oligomers have been prepared as synthetic models for active sites of enzymes and mimic systems of photosynthesis or photoharvesting.18-22 Although a number of Pr and Pc compounds with chiral substituents have been synthesized so far, most of the studies have focused on their aggregation behavior in a solution or on the solid-state monolayer transferred from an air/liquid interface onto a substrate using Langmuir-Blodgett (LB) technique.23-25 A liquid-liquid interface has received a great deal of attention in various fields of chemistry and biochemistry.26 We have interest (11) Shinoda, S.; Okazaki, T.; Player, T. N.; Misaki, H.; Hori, K.; Tsukube, H. J. Org. Chem. 2005, 70, 1835. (12) Wu, Z.; Yang, G.; Chen, Q.; Liu, J.; Yang, S.; Ma, J. S. Inorg. Chem. Commun. 2004, 7, 249. (13) Kawamoto, T.; Hammes, B. S.; Haggerty, B.; Yap, G. P. A.; Rheingold, A. L.; Borovik, A. S. J. Am. Chem. Soc. 1996, 118, 285. (14) Morino, K.; Oobo, M.; Yashima, E. Macromolecules 2005, 38, 3461. (15) Goto, H.; Zhang, H. Q.; Yashima, E. J. Am. Chem. Soc. 2003, 125, 2516. (16) Nonokawa, R.; Yashima, E. J. Am. Chem. Soc. 2003, 125, 1278. (17) For example; (a) Leznoff, C. C., Lever, A. B. P., Eds. Phthalocyanines: Properties and Applications, Vol. 1; VCH: New York, 1989; Vol.2, 1992; Vol.3, 1993; Vol.4, 1996. (b) Okura, I.; Photosensitization of Porphyrins and Phthalocyanines; Gordon and Breach Science: Amsterdam, The Netherlands, 2000. (18) Furutsu, D.; Satake, A.; Kobuke, Y. Inorg. Chem. 2005, 44, 4460. (19) Takahashi, R.; Kobuke, Y. J. Org. Chem. 2005, 70, 2745. (20) Ishii, K.; Watanabe, Y.; Abiko, S.; Kobayashi, N. Chem. Lett. 2002, 450. (21) Kobayashi, N.; Muranaka, A.; Nemykin, V. N. Tetrahedron Lett. 2001, 42, 913. (22) Kimura, M.; Hamakawa, T.; Muto, T.; Hanabusa, K.; Shirai, H.; Kobayashi, N. Tetrahedron Lett. 1998, 39, 8471. (23) Kobayashi, N. Coord. Chem. ReV. 2001, 219-221, 99. (24) Engelkamp, H.; Middelbeek, S.; Nolte, R. J. M. Science 1999, 284, 785. (25) Kobayashi, N.; Higashi, R.; Titeca, B. C.; Lamote, F.; Ceulemans, A. J. Am. Chem. Soc. 1999, 121, 12018.

10.1021/la0526131 CCC: $33.50 © 2006 American Chemical Society Published on Web 01/21/2006

J-Aggregate of MgPc(SEtPh)8-Pd(II) Complexes Scheme 1. Reaction Routes for the Syntheses of Eight Chiral Thioether-Substituted Phthalocyaninatomagnesium(II)a

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dichroism (CD) measurements combined with the centrifugal liquid-membrane (CLM) apparatus.34,35 From the detailed investigations on the structure of the interfacial aggregates by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF/MS) and scanning electron microscope (SEM) techniques, the formation of suprahelical structure of MgPc(SEtPh)8 molecules bridged by Pd(II) coordination between the adjacent molecules was suggested.

2. Results and Discussion

a Lower illustrations are twisted conpormations of eight chiral thioether substituents.

in the liquid/liquid interface from the viewpoint of a novel twodimensional nanoreaction field like a biological membrane27,28 and investigated the adsorption and aggregation behaviors of dye molecule by means of various methods.29-31 Quite recently, we observed that the two-dimensional high-ordered J-aggregate of thioether-substituted phthalocyanine and subphthalocyanine derivatives were formed at the toluene/water interface upon the addition of Pd(II) into the system.32,33 Inspired by this finding, we extended the kind of strategy such as that in the present study by initially synthesizing novel phthalocyanine derivatives with eight chiral thioether substituents on the peripheral position of ((2,3,9,10,16,17,23,24-octakis-1phenylethylthiophthalocyaninato)magnesium(II) [MgPc(SEtPh)8], see Scheme 1), and by investigating their aggregation behaviors after the addition of Pd(II) in toluene and at the toluene/ water interface by means of UV-vis absorption and circular (26) Watarai, H., Teramae, N., Sawada, T., Eds. Interfacial Nanochemistry: Molecular Science and Engineering at Liquid-Liquid Interfaces (Nanostructure Science and Technology); Plenum: New York, 2005. (27) Volkov, A. G., Ed. Liquid Interfaces in Chemical, Biological and Pharmaceutical Applications; Marcel Dekker: New York, 1997. (28) Watarai, H.; Tsukahara, S.; Nagatani, H.; Ohashi, A. Bull. Chem. Soc. Jpn. 2003, 6, 1471. (29) Fujiwara, K.; Monjushiro, H.; Watarai, H. ReV. Sci. Instrum. 2005, 76, 023111. (30) Yulizar, Y.; Monjushiro, H.; Watarai, H. J. Colloid Interface Sci. 2004, 275, 560. (31) Fujiwara, N.; Tsukahara, S.; Watarai, H. Langmuir 2001, 17, 5337. (32) Adachi, K.; Watarai, H. J. Mater. Chem. 2005, 15, 4701. (33) Adachi, K.; Chayama, K.; Watarai, H. Soft Matter 2005, 1, 292.

2.1. Synthesis and Characterization of Phthalocyanine Derivatives with Chiral Thioether Substitutes. Optically active thioether-substituted magnesium phthalocyanines (MgPc(SEtPh)8) were synthesized as shown in Scheme 1. Linstead tetracyclization36 of the phthalocyanine precursors, Pn(SEtPh)2, in the presence of magnesium butoxide gave MgPc(SEtPh)8, which was soluble in a number of common organic solvents including chloroform, dichloromethane, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), and toluene, but insoluble in apolar hydrocarbon solvents such as n-hexane. The overall yield of this sequence was ca. 40-50% (see Experimental Section). These compounds were identified by 1H NMR and MALDI-TOF/MS spectra and elemental analyses. Generally, Pc compounds tend to interact with each other by attractive π-π stacking due to their extended flat aromatic surface, which prefers face-to-face aggregation.17,37,38 The aggregation of MgPc(SEtPh)8 compounds was detected using absorption spectroscopy, as shown in Figure 1b. At low concentrations of (R)-MgPc(SEtPh)8, the typical Q-band with D4h symmetry17 was observed at 710 nm, while at higher concentrations this peak disappeared and a new peak emerged around 680 nm with isosbestic points at 626, 648, 691, and 725 nm. The shape with the absorption maximum wavelength of the Q-band is known to be a sensitive probe in determining the Pc aggregation types.39 In this case, the blue-shifted, broad, and intensity lowered Q-band is indicative of the presence of the MgPc(SEtPh)8 dimer with face-to-face comformation.40,41 Other (S)- and (rac)-MgPc(SEtPh)8 systems showed similar spectral changes (not shown). To obtain the dimerization constant, Kd, of MgPc(SEtPh)8 compounds in toluene, the absorption coefficient at 710 nm was plotted as a function of MgPc(SEtPh)8 total concentration, assuming the following monomer (M) and dimer (D) equilibrium; Kd

2monomer y\z dimer Kd )

[D] [M]2

(1) (2)

Using the monomer molar absorptivity, M, obtained from the absorbance in the dilute solution (500 nm), suggesting that the aggregate of MgPc(SEtPh)8Pd(II) complexes tends to grow into a bundle of one-dimensional molecular wire and is stably formed. Since CD measurements confirmed the formation of optically chiral aggregate on the molecular level, it can be expected that the optical chirality should

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Adachi et al. Scheme 5. (a) Diagrammatic Representation of Exciton Coupling of the Left-handed Phthalocyanine J-Type Dimera and (b) Contribution of Exciton Coupling in Expected (Left) and Observed (Right) UV-Vis Absorption (Upper) and CD (Lower) Spectra

Figure 6. (a) MALDI-TOF mass spectra (positive ion) of the aggregate of (R)-MgPc(SEtPh)8-Pd(II) complexes formed at the toluene/water interface. The inset in a shows a closer view of hexamer [5MgPc(SEtPh)8-12(PdCl2)] peak region. (b) Possible structure of the interfacial aggregate of MgPc(SEtPh)8 with palladium(II) ion. The sphere represents a PdCl2. For the assignment of the peaks, see the text.

a The solid and broken arrows represent allowed and forbidden transitions, respectively.

Figure 7. Typical field-emission scanning electron microscope (FESEM) images of an interfacial aggregate of (a) (R)-MgPc(SEtPh)8Pd(II) and (b) (S)-MgPc(SEtPh)8-Pd(II) complexes. In b a slightly twisted fiber can be clearly seen.

generate any chiral morphology of the aggregate fibers. However, an observation of a particular chiral structure in the fibers was difficult because of the low degree of twisting and the lack of fiber length. Nevertheless, we fortunately found that the aggregate of (S)-MgPc(SEtPh)8-Pd(II) complexes with positive chirality have right-handed helical structure (Figure 7b). It should be emphasized that this result allows us, for the first time, to correlate the handedness of the supramolecular morphology of the interfacial aggregate to the sign of the optical CD spectra. 2.5. Absolute Configuration of Interfacial Aggregate from Exciton Chirality Theory. From the above results of UV-vis absorption, CD, and MALDI-TOF/MS spectra and SEM image, we now consider the exciton chiral effect that is induced in the Q-band region of MgPc(SEtPh)8 by interfacial aggregate of MgPc(SEtPh)8-Pd(II) complexes. As a typical case, we discuss on a

left-handed J-type dimer, as shown in Scheme 5a. The exciton splitting energy of the dimer depends on its geometry.56 In general, transition dipoles aligned to give a repulsive electrostatic interaction will result in a rising of the transition energy (blue shift), while the transition dipoles arranged to give an attractive electrostatic interaction will result in a lowering of the transition energy (red shift). Phthalocyanine compounds have orthogonal two transition dipoles for the lowest transitions (Q-band) on Pc skeleton plate.57,58 The mutual orientation of any couple of transition dipoles of the J-type dimer of MgPc(SEtPh)8-Pd(II) complexes formed at the interface may be streamlined into one exciton coupling energy diagram on the basis of Kasha’s theory,59 as shown in Scheme 5a, which can predict the absorption and CD spectra of the dimer. A couple of transition dipoles arranged in the head-to-tail configuration exhibits a red-shifted absorption band, because the excited state is most stabilized. In this case, since dipoles do not form a chiral array, no CD signals are observed. On the other hand, in the oblique orientations (chiral (56) Kobayashi, T., Ed. J-Aggregates; World Scientific: Singapore, 1996. (57) Lucia, E. A.; Verderame, F. D.; Taddei, G. J. Chem. Phys. 1970, 52, 2307. (58) Hush, N. S.; Woolsey, I. S. Mol. Phys. 1971, 21, 465. (59) Kasha, M.; Rawls, H. R.; El-Bayoumi, M. A. Pure Appl. Chem. 1965, 11, 371.

J-Aggregate of MgPc(SEtPh)8-Pd(II) Complexes

configurations), both exciton transitions are allowed. Thus, the absorption spectrum will be observed as two bands, and a bisignate CD curve will result from overlapping positive and negative Cotton effects. Thus, the estimated absorption spectrum has three bands that are correlated to the observed one with two shoulder peaks at 687 and 719 nm in the (R)-MgPc(SEtPh)8-Pd(II) system, regardless of the intensity of each absorption band. Furthermore, the estimated CD signal, having the negative chirality, is also in good agreement with experimental result, as shown in Scheme 5b. Moreover, in the case of a linear pentamer, which was observed in the stoichiometic analysis described in the above section, the pitch size corresponding to the distance between the centers of neighboring MgPc(SEtPh)8 molecules was calculated as ca. 10 Å from the exciton coupling model using the values of the blue shift (710 nm f 687 nm; 471 cm-1) and the red shift (710 nm f 719 nm; -176 cm-1) in the Q-band of the J-type linear pentamer.52 This pitch size seems to be reasonable from the view of the related MgPc crystal structure60 and the CPK model of the MgPc(SEtPh)8 molecule. The excellent agreement between the estimated and the observed spectra strongly supported the proposed helical J-aggregate structure for MgPc(SEtPh)8-Pd(II) complexes formed at the toluene/water interface.

3. Conclusion This study represented a new strategy to design chiral supramolecular assemblies of phthalocyanine (Pc) compound based on noncovalent interactions using a liquid/liquid interface. The experimental results indicated that the liquid/liquid interface is valuable as a two-dimensional reaction field where is accessible solvophobic or amphipathic compounds from the organic and aqueous phases. The self-assembly and Pd(II)-induced aggregate of the MgPc(SEtPh)8 compound in toluene showed a blue shift in the Q-band region and definite CD activity, suggesting the formation of a twisted H-type dimer. On the other hand, in the toluene/water system, the interfacial aggregate of MgPc(SEtP)8Pd(II) complexes indicated a red-shifted absorption spectrum and specific CD effect, resulting from helical J-aggregate formation. Interestingly, the difference in the form of aggregate between the dry toluene solution and the toluene/water interface suggests that the structure of the Pc aggregate can be controlled by using the liquid/liquid interface template. Moreover, we also have provided evidence in both systems that the helical arrangement of Pc aggregate can be tailor-made by the introduction of chiral substituents onto the peripheral position. The stoichiometric and aggregation number, and the structure of MgPc(SEtPh)8-Pd(II) complexes were investigated by means of CLM-Abs, CLM-CD, MALDI-TOF/MS, and SEM measurements, so that the most probable model for optically active helical aggregate could be proposed by comparing with the exciton chirality theory. However, to elucidate the detailed helical supramolecular structure of the Pc aggregate formed at the interface, further investigations on a series of Pc compounds with other chiral substituents will be necessary. We believe that these optically active metal-induced Pc aggregates would be useful not only as conventional chiral organic-inorganic materials but also as candidates for switch-functionalized assemblies (such as chiral memory) by magnetooptic effect, photochemical reactions, and elsewhere. 4. Experimental Section Unless specified in particular, all measurements in this study were carried out under the condition that the ionic strength and pH were fixed at 0.1 M (1 M ) 1 mol dm-3) and 2.0 with sodium chloride (60) Templeton, D. H.; Fischer, M. S.; Zalkin, A.; Calvin M. J. Am. Chem. Soc. 1971, 93, 2622.

Langmuir, Vol. 22, No. 4, 2006 1637 and sulfuric acid, respectively, in a thermostated room at 25 ( 2 °C. In this condition, Pd(II) exists as PdCl42- in the aqueous phase.61 4.1. Materials. 1-Butanol, tetrahydrofuran, chloroform, and toluene were purchased from Nacalai Tesque Inc. (Kyoto, Japan). 1-Butanol and tetrahydrofuran were freshly distilled after drying over molecular sieves before use. Chloroform was shaken three times with 2 M potassium hydroxide solution, followed by shaking three times with water, dried over calcium chloride, and then fractionally distilled. Toluene was purified according to a reported method,62 and then saturated with distilled water immediately before use. Water was distilled and deionized by a Milli-Q system (Millipore, USA). (R)- and (S)-1-Phenylethyl alcohol were purchased from Tokyo Kasei Kogyo Co., Ltd. (>99% ee, Tokyo, Japan). All other chemicals were of reagent grade from Wako Pure Chemicals (Osaka, Japan), and were used as received without further purification. 4.2. Synthesis of Optically Active Thio Ether-Substituted Phthalocyanine Derivatives. 1-Phenylethanethiol [PhEtSH]. The appropriate 1-phenylethanol (25.0 g, 0.20 mol) was dissolved in concentrated hydrochloric acid (150 mL); thiourea (22.8 g, 0.30 mmol) was then added and the reaction mixture refluxed for 18 h under nitrogen atmosphere. After cooling to room temperature, 6 M sodium hydroxide solution was added up to pH 10 and the reaction mixture heated to a gentle reflux for 3 h under nitrogen atmosphere. After the resulting suspension was acidified with concentrated hydrochloric acid, the crude reaction mixture extracted with diethyl ether and then dried over anhydrous sodium sulfate. After removal of the solvent, the residue was distilled under reduced pressure (10 Torr, 105-110 °C) and yielded PhEtSH as a colorless oil. (a) (R)-PhEtSH. Yield of the compound: 21.3 g (76.9% on the basis of (R)-1-phenylethanol); 1H NMR (300 MHz, CDCl3) δ 1.65 (d, 3H, -CH3), 1.95 (d, 1H, -SH), 2.53 (qd, 1H, Ph-CH-), 7.1-7.4 (m, 5H, Ph); 13C NMR (75 MHz, CDCl3) δ 48.1, 127.5, 128.1, 128.9, 143.7. (b) (S)-PhEtSH. Yield of the compound: 20.5 g (74.1% on the basis of (S)-1-phenylethanol); 1H NMR (300 MHz, CDCl3) δ 1.65 (d, 3H, -CH3), 1.95 (d, 1H, -SH), 2.53 (qd, 1H, Ph-CH-), 7.1-7.4 (m, 5H, Ph); 13C NMR (75 MHz, CDCl3) δ 48.1, 127.5, 128.1, 128.9, 143.7. (c) (rac)-PhEtSH. Yield of the compound: 22.2 g (80.3% on the basis of (rac)-1-phenylethanol); 1H NMR (300 MHz, CDCl3) δ 1.65 (d, 3H, -CH3), 1.95 (d, 1H, -SH), 2.53 (qd, 1H, Ph-CH-), 7.1-7.4 (m, 5H, Ph); 13C NMR (75 MHz, CDCl3) δ 48.1, 127.5, 128.1, 128.9, 143.7. 4,5-Bis(1-phenylethanethio)phthalonitrile [Pn(SEtPh)2]. 1,2Dichloro-4,5-nitrophthalonitrile (3.00 g, 15.2 mmol) was dissolved in anhydrous THF (50 mL) under nitrogen atmosphere, and the appropriate PhEtSH compound (6.20 g, 45.0 mmol) was added. After stirring for 30 min, finely ground anhydrous potassium carbonate (9.75 g, 70.7 mmol) was added in portions over 1 h with efficient stirring. The reaction mixture was stirred at 40 °C for 24 h under nitrogen atmosphere. Then the solution was poured into ice water (200 mL). The precipitate was filtered off, washed with water until the filtrate was neutral, and dried in vacuo. Purification of the product was accomplished by silica gel column chromatography (eluent: CHCl3:MeOH ) 9:1). Rotary evaporation of the solvent gave Pn(SEtPh)2 as a colorless crystalline solid. (a) (R)-Pn(SEtPh)2. Yield of the compound: 4.58 g (76.2% on the basis of (R)-1,2-dichloro-4,5-nitrophthalonitrile); 1H NMR (300 MHz, CDCl3) δ 1.65 (d, 3H, -CH3), 4.44 (q, 2H, S-CH-Ph), 7.157.25 (m, 12H, -Ph and Ar); 13C NMR (75 MHz, CDCl3) δ 23.3, 47.2, 111.9, 115.4, 127.1, 128.3, 129.1, 131.8, 141.2, 144.2; FT-IR (KBr, cm-1) 3055, 3024, 2979, 2921, 2865, 2229 (CtN), 1564, 1493, 1452, 1373, 1350, 1222 (C-S-C), 1100, 1058, 1025, 923, 767, 700, 529. Anal. Calcd for C24H20N2S2: C, 71.96; H, 5.03; N, 6.99%. Found: C, 72.17; H, 4.87; N, 6.52%. (b) (S)-Pn(SEtPh)2. Yield of the compound: 4.25 g (70.8% on the basis of (S)-1,2-dichloro-4,5-nitrophthalonitrile); 1H NMR (300 (61) Baes, C. F., Jr.; Mesmer, R. E. The Hydrolysis of Cations; John Wiley & Sons: New York, 1974. (62) Riddick, J. A.; Bunger, W. B.; Sakano, T. K. Organic SolVents, 4th ed.; John Wiley & Sons: New York, 1986.

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MHz, CDCl3) δ 1.65 (d, 3H, -CH3), 4.44 (q, 2H, S-CH-Ph), 7.147.30 (m, 12H, -Ph and Ar); 13C NMR (75 MHz, CDCl3) δ 23.3, 47.2, 111.9, 115.4, 127.1, 128.3, 129.1, 131.8, 141.2, 144.2; FT-IR (KBr, cm-1) 3061, 3019, 2977, 2924, 2863, 2225 (CtN), 1567, 1487, 1450, 1374, 1348, 1224 (C-S-C), 1102, 1058, 1022, 926, 765, 699, 525. Anal. Calcd for C24H20N2S2: C, 71.96; H, 5.03; N, 6.99%. Found: C, 71.97; H, 5.27; N, 7.22%. (c) (rac)-Pn(SEtPh)2. Yield of the compound: 4.36 g (72.5% on the basis of (rac)-1,2-dichloro-4,5-nitrophthalonitrile); 1H NMR (300 MHz, CDCl3) δ 1.65 (d, 3H, -CH3), 4.44 (q, 2H, S-CH-Ph), 7.167.27 (m, 12H, -Ph and Ar); 13C NMR (75 MHz, CDCl3) δ 23.3, 47.2, 111.9, 115.4, 127.1, 128.3, 129.1, 131.8, 141.2, 144.2; FT-IR (KBr, cm-1) 3059, 3023, 2974, 2925, 2864, 2226 (CtN), 1564, 1490, 1452, 1376, 1348, 1229 (C-S-C), 1108, 1058, 1024, 928, 765, 701, 527. Anal. Calcd for C24H20N2S2: C, 71.96; H, 5.03; N, 6.99%. Found: C, 72.25; H, 4.98; N, 7.34%. (2,3,9,10,16,17,23,24-Octakis-1-phenylethylthiophthalocyaninato)magnesium(II) [MgPc(SEtPh)8]. Following the classic procedure of Linstead macrocyclization,36 Mg turnings (0.416 g, 17.1 mmol) were stirred in 1-butanol (20 mL) at reflux under nitrogen atmosphere for 24 h with the aid of iodine crystal (ca. 0.1 g) as initiator. The appropriate Pn(SEtPh)2 compound (2.00 g, 5.00 mmol) was added to the resulting magnesium butoxide suspension, and the reaction mixture was stirred at reflux under nitrogen atmospheres for 6 h and allowed to cool to room temperature. Following rotary evaporation, the resulting green-black residue was dissolved in chloroform and filtered, and the resulting solution was washed with 25 mL of water four times, dried over anhydrous magnesium sulfate. Rotary evaporation and silica gel chromatography (eluent: CHCl3:MeOH ) 9:1) gave MgPc(SEtPh)8 as a dark green solid. (a) (R)-MgPc(SEtPh)8. Yield of the compound: 0.90 g (44.4% on the basis of (R)-Pn(SEtPh)2); 1H NMR (300 MHz, DMSO-d6) δ 2.07 (d, 24H, -CH3), 5.24 (q, 8H, S-CH-Ph), 7.30 (t, 8H, Ph(1)), 7.47 (t, 16H, Ph(2)), 7.82 (d, 16H, Ph(3)); MALDI-TOF/MS m/z 1626 (M+) [matrix: R-cyano-4-hydroxycinnamic acid (R-CHCA)]. Anal. Calcd for C96H80N8S8Mg: C, 70.89; H, 4.96; N, 6.89%. Found: C, 71.15; H, 4.98; N, 7.14%. UV-vis (toluene) λmax/nm (log /(M-1 cm-1)) 378 (4.80), 638 (4.49), 680 (sh), 710 (5.23). (b) (S)-MgPc(SEtPh)8. Yield of the compound: 0.98 g (48.3% on the basis of (S)-Pn(SEtPh)2); 1H NMR (300 MHz, DMSO-d6) δ 2.07 (d, 24H, -CH3), 5.24 (q, 8H, S-CH-Ph), 7.30 (t, 8H, Ph(1)), 7.47 (t, 16H, Ph(2)), 7.82 (d, 16H, Ph(3)); MALDI-TOF/MS m/z 1626 (M+) [matrix: R-cyano-4-hydroxycinnamic acid (R-CHCA)]. Anal. Calcd for C96H80N8S8Mg: C, 70.89; H, 4.96; N, 6.89%. Found: C, 70.65; H, 4.71; N, 7.12%. UV-vis (toluene) λmax/nm (log /(M-1 cm-1) 378 (4.82), 638 (4.50), 680 (sh), 710 (5.26). (c) (rac)-MgPc(SEtPh)8. Yield of the compound: 0.81 g (39.5% on the basis of (rac)-Pn(SEtPh)2); 1H NMR (300 MHz, DMSO-d6) δ 2.07 (d, 24H, -CH3), 5.24 (q, 8H, S-CH-Ph), 7.30 (t, 8H, Ph(1)), 7.47 (t, 16H, Ph(2)), 7.82 (d, 16H, Ph(3)); MALDI-TOF/MS m/z 1626 (M+) [matrix: R-cyano-4-hydroxycinnamic acid (R-CHCA)]. Anal. Calcd for C96H80N8S8Mg: C, 70.89; H, 4.96; N, 6.89%. Found: C, 70.77; H, 5.12; N, 7.25%. UV-vis (toluene) λmax/nm (log /(M-1 cm-1)) 378 (4.81), 638 (4.49), 680 (sh), 710 (5.24). 4.3. High-Speed Stirring (HSS) Method. The interfacial adsorption of MgPc(SEtPh)8 compounds in the toluene/water system was measured using the high-speed stirring (HSS) method.50 The principle of the HSS method was described elsewhere,63 and the analogous procedure was employed.37,64 Briefly, the toluene phase of MgPc(SEtPh)8 (50 mL) and the aqueous phase (50 mL) fixing pH 2 were agitated at a stirring rate of 5000 and 200 rpm in the glass stir cell. The toluene phase was continuously separated from the agitated mixture by means of a PTFE phase separator, and phase circulated through a flow cell at a flow rate of ca. 20 mL min-1 by an electric pump (Flumax Junior, Fluid Metering Inc., Japan). Absorption spectra of the separated organic phase were measured in the range of 300-850 nm using a photodiode-array UV-vis detector (SPD-M 6A, Shimadzu, Japan). We could determine the

interfacial concentration of MgPc(SR)8 derivatives by evaluating the difference between the absorbances of the toluene phase under a high-speed stirring (5000 rpm) and a low-speed stirring (200 rpm) at the absorption maximum wavelength. In the present system, Langmuir isotherm was given by65

(63) Watarai, H.; Cunnlngham, L.; Frelser, H. Anal. Chem. 1982, 54, 2390. (64) Ohashi, A.; Tsukahara, S.; Watarai, H. Anal. Chim. Acta 1998, 364, 53.

(65) Nagatani, H.; Watarai, H. Chem. Lett. 1997, 167. (66) Watarai, H.; Gotoh, M.; Gotoh, N. Bull. Chem. Soc. Jpn. 1997, 70, 957.

[MgPc(SEtPh)8]i )

aK′[MgPc(SEtPh)8]o a + K′[MgPc(SEtPh)8]o

(9)

where [MgPc(SEtPh)8]i and [MgPc(SEtPh)8]o denote the concentrations of MgPc(SEtPh)8 adsorbed at the toluene/water interface (mol/ dm2) and in the bulk toluene phase (mol/dm3), respectively. a and K′ are the saturated interfacial concentration (mol/dm2) and the interfacial adsorption constant of MgPc(SEtPh)8, respectively. The difference between the absorbances of the toluene phase under the high-speed (5000 rpm) and low-speed (200 rpm) stirring conditions, ∆A, and the absorbance of the bulk toluene phase, Ao, under high-speed stirring can be written as ∆A ) l[MgPc(SEtPh)8]i

Si Vo

Ao ) l[MgPc(SEtPh)8]o

(10) (11)

where , l, Si, and Vo are the molar absorptivity in toluene, the optical path length, the total interfacial area and the organic phase volume, respectively. The total interfacial area in the toluene/water system was reported as 2.0 × 102 dm2.66 4.4. UV-Vis Absorption and Circular Dichroism Spectra Measurement Using Centrifugal Liquid-Membrane (CLM) Technique. The interfacial formation of the optically active aggergate of MgPc(SEtPh)8-Pd(II) complexes in the toluene/water system was directly observed using the CLM-Abs and CLM-CD),34,35 in which the UV-vis spectrophotometer (8453, Agilent, USA) and spectropolarimeter (J-810E, JASCO, Japan) combined the CLM method to measure UV-vis absorption and CD spectra, respectively, of the interfacial species. The apparatus for the CLM-Abs and CLM-CD measurements were essentially the same with the one reported previously.35 A cylindrical cell, whose height and outer diameter were 3.3 and 2.1 cm, respectively, was placed horizontally in the sample chamber and rotated at 10 000 rpm by a speed-controlled electric motor (NE-22E, Nakanishi Inc., Japan). The toluene solution of MgPc(SEtPh)8 and the aqueous solution of Pd(II) (each 0.500 mL) were introduced into the cylindrical cell using a microsyringe. The sum of UV-vis absorption or CD spectra of both bulk phases and the interface was measured in the range of 330-850 nm. The values of the thickness of the toluene and aqueous phases were 293 and 289 µm, respectively. The interfacial area (Si) between two phases was calculated as 17.3 cm2. The aqueous phase with Pd(II) and the toluene phase without MgPc(SEtPh)8 in the CLM cell was used for a baseline measurement. 4.5. Sample Preparation and Characterization for MALDITOF/MS and SEM Measurements. The interfacial aggregate of MgPc(SEtPh)8-Pd(II) complexes at the toluene/water interface were deposited onto MALDI-TOF/MS sample plate (PT-100, PerSeptive Biosystems, U.K.) and a gold sputtered glass plate for MALDITOF/MS and SEM measurements, respectively, by using a previously reported method.32 Mass spectra of the interfacial aggregate of MgPc(SEtPh)8-Pd(II) complexes were recorded by Voyager DE-PRO instrument (PerSeptive Biosystems, U.K.) with 2,5-dihydroxybenzoic acid (DHB) as a matrix. The gold glass plate was then allowed to dry in air. This sample was coated with Pt using an auto fine coater (JEE-420T, JEOL, Japan). The morphology of the aggregate was confirmed by means of a field emission scanning electron microscopy (FE-SEM) microscope (JSM-6340F, JEOL, Japan) operating at 5 kV. 4.6. Other Apparatus. UV-visible and CD spectra in toluene solution were obtained on a V-570 spectrometer (JASCO, Japan)

J-Aggregate of MgPc(SEtPh)8-Pd(II) Complexes and J-810 spectropolarimeter (JASCO, Japan), respectively. NMR (CDCl3 and DMSO-d6 data were obtained at 298 K unless otherwise stated (δ (ppm) vs tetramethylsilane (TMS)) with Unity 300 spectrometer (Varian, USA). Elemental analyses were performed using a CHNS/O analyzer 2400 (Perkin-Elmer, USA). Chromatographic separations were obtained using Wakogel C-200 (silica gel, Wako, Japan). FT-IR spectra (KBr tablets) were recorded at room temperature on a MAGNA-IR 560 spectrometer (Nicolet, USA). pH values of the aqueous phase were conducted using a F-14 pH meter (HORIBA, Japan) equipped with a 6366-10D glass electrode.

Acknowledgment. This study was supported by the Grantin-Aid for Scientific Research (S) (No. 16105002) of the Ministry

Langmuir, Vol. 22, No. 4, 2006 1639

of Education, Culture, Sports, Science and Technology of Japan. K.A. thanks Dr. Shingo Ikeda for technical and helpful discussions about the FE-SEM measurements. K.A. is a Ph.D student supported by the MORESCO contact education program. Supporting Information Available: MALDI-TOF/MS spectrum of MgPc(SEtPh)8-Pd(II) aggregate formed in toluene, effect of various metal ions on absorption and CD spectra of MgPc(SEtPh)8 in toluene (PDF). This material is available free of charge via the Internet at http://pubs.acs.org. LA0526131