Role of Hydrophobic Interaction in Controlling the Orientation of

Article pubs.acs.org/JPCC

Role of Hydrophobic Interaction in Controlling the Orientation of Dicationic Porphyrins on Solid Surfaces Miharu Eguchi,†,‡ Tetsuya Shimada,§ Donald A. Tryk,∥ Haruo Inoue,§,* and Shinsuke Takagi§,* †

Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571 Japan ‡ PRESTO (Precursory Research for Embryonic Science and Technology), Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama 332-0012 Japan § Department of Applied Chemistry, Graduate Course of Engineering, Tokyo Metropolitan University, 1-1 minami-ohsawa, Hachioji, Tokyo 192-0397 Japan ∥ Fuel Cell Nanomaterials Center, University of Yamanashi, 6-43 Miyamaecho, Kofu, Yamanashi 400-0021 Japan ABSTRACT: The adsorption orientational behavior of dicationic porphyrins on clay surfaces in various solvents was examined. Addition of aprotic solvents to the aqueous solution containing the clay−porphyrin complex induced a large spectral shift to shorter wavelength. The blue shift turned out to be due to the orientation angle change of porphyrin, which leads to the relaxation of molecular flattening. From dichroic measurements on a waveguide, the orientation of the porphyrin was directly observed and found to be parallel to the clay surface in water and to be at a tilt angle of 68° with respect to the clay surface in DMF. A thermodynamic study of the porphyrin orientation on the clay surface was undertaken. This analysis showed that the parallel orientation of the porphyrin was stabilized mainly by the entropy term, and the tilted orientation was stabilized mainly by the enthalpy term. Furthermore, the effects of different organic solvents on porphyrin orientation on the clay surface were examined, and strong correlation between hydrogen bonding parameters and orientation change was found. composed of synthetic clays and cationic dyes.35−53 Yamagishi et al. reported stereoselective adsorption on a clay surface modified by optically active metal complexes. The extremely flat clay surface and its interaction with adsorbed molecules provide a means of tuning the functionality of the composite.30,31 We have been able to prepare unique complexes in which porphyrin molecules adsorb on clay23−25 surfaces without any aggregation.41−53 The crucial factor for the high-density adsorption of porphyrins with controlled intermolecular distance is the matching of intercharge distances on the clay and the porphyrin, that is, the distance between negatively charged sites on the clay sheet and that between positively charged sites in the porphyrin molecule (sizematching effect). This technique is a novel methodology to control molecular alignment using specific host−guest interactions. In these complexes, the charge density on the clay surface controls the distances between porphyrins at 2.4 nm, at which there are discernible interactions between porphyrins in the ground state, and the excited state lifetimes for the porphyrins adsorbed on the clay are sufficiently long to allow photochemical reactions.42,48,51 Tetracationic porphyrins adsorb in a parallel orientation with respect to the clay surface.

1. INTRODUCTION Recently, nanotechnology has been attracting much interest in both scientific and technological fields.1,2 With the aim of structural control at the molecular level, techniques based on chemical interactions have been widely studied.3 Porphyrin derivatives have been frequently used as molecular units or building blocks due to their multifunctionality.4,5 Many methods have been developed to construct porphyrin assemblies, including: (i) self-assembly using guest−guest interactions such as van der Waals interaction and hydrogen bonding;6−10 (ii) supermolecules using covalent bonds;11−16 and (iii) self-assembly on single crystalline substrates.17−22 In these methods, the interactions between the porphyrin molecules determine the structure of the porphyrin assembly. Several researchers have also turned their attention to layered materials such as clay minerals to construct ordered molecular structures.23−34 Thus far, we have reported unique porphyrin assemblies on layered materials using specific host−guest interactions. Clay minerals provide unique inorganic surfaces. Their surfaces can possess anionic charge intrinsic to their structure, and they are extremely flat even at the atomic level. The typical particle sizes are in the 10 to ∼1000 nm range. In the case of synthetic clays, the purity is very high, and there is a complete lack of color. They can disperse in aqueous solvents with perfect transparency. Thus, many researchers have investigated complexes © 2013 American Chemical Society

Received: January 19, 2013 Revised: April 4, 2013 Published: April 11, 2013 9245

dx.doi.org/10.1021/jp400645d | J. Phys. Chem. C 2013, 117, 9245−9251

The Journal of Physical Chemistry C

Article

Figure 1. Structures of 4+ and 2+ charged cationic porphyrins.

porphyrin solutions. The less polar solvents, which were miscible with water, were added to the clay−SSA water dispersion. The SSA concentration was 20 mg L−1 unless otherwise noted. The loading level of porphyrin molecules was 10% versus the CEC of the clay. The concentration of anionic sites of clay in solution was calculated to be 2.0 × 10−5 eq L−1 from the CEC of the clay. By means of this procedure, the TMPyP4+ and trans-DPyP2+ and cis-DPyP2+ were combined with SSA respectively. Film Sample for Dichroic Measurements. Cast films for dichroic measurements were prepared as follows. The surface of a quartz waveguide was washed with concentrated H2SO4 to enhance the hydrophilicity. Subsequently, the quartz surface was rinsed with 1 M NaOH, 1 M HCl, and a large amount of ion-exchanged water. An aliquot of aqueous solution (3.5 μL) containing the nanolayered compound (1.0 × 10−4 eq L−1) was pipetted onto the hydrophilic quartz waveguide, and the water was allowed to evaporate at room temperature. Subsequently, an aliquot of aqueous porphyrin solution (1.0 × 10−5 M, 3.5 μL) was pipetted onto the cast film of nanolayered compound, and the excess was washed away with deionized water. The area on the quartz waveguide covered with the complex was approximately 1.5 cm2. The details of the sample preparation were reported in a previous article.45 Thus, a sample was obtained, in which the porphyrin−clay complex was mostly adsorbed on the waveguide as a monolayer parallel to the waveguide surface as shown in Figure 2.

In this article, the control of molecular orientation with respect to the substrate, as the next stage of advanced structure control following the control of molecular alignment, is described. Specifically, the dicationic porphyrin orientation angle on the clay surface was examined. A thermodynamic study of the porphyrin orientation on the clay surface was also carried out to rationalize the orientational behavior. Photochemical reaction efficiency at the surface of inorganic compounds such as electron transfer and energy transfer are believed to depend on their orientation. Nevertheless, they have not been studied well because of the complexity owing to the roughness of the inorganic compound surface. In this study, the clay surface was adopted as an ideal flat inorganic surface to elucidate the molecular adsorption behavior.

2. EXPERIMENTAL SECTION Chemicals. The tetracationic porphyrin (tetrakis(1-methylpyridinium-4-yl) porphyrin (TMPyP) was purchased from Aldrich; the counterion was replaced by chloride by use of an ion exchange column (ORGANO AMBERLITE IRA400JCL). The dicationic porphyrins ((cis-bis(N-methylpyridinium-4-yl)diphenylporphine (cis-DPyP) and trans-bis(N-methylpyridinium-4-yl)diphenylporphine) (trans-DPyP)) were purchased from Mid-Century Chemicals (Figure 1). The purity was checked by TLC. Sumecton SA (SSA) synthetic clay was obtained from Kunimine Industries Co., Ltd. The diameters of the clay particles were in the 20−50 nm range from AFM measurements. The sample was purified by repeated decantation from water and was washed with ethanol. The cation exchange capacity (CEC) was 99.7 meq/100 g. The amounts of water in the SSA and porphyrin reagent were measured by TG/ DTA (SHIMADZU DTG-60H). Their molecular weights were corrected according to the TG measurements. Water was deionized just before use with an ORGANO BB-5A system (PF filterX2+G-10 column). Organic solvents for spectroscopy were obtained from Kanto Chemical Co., Inc. (spectral grade) and used without further purification. Equipment. TG-DTA measurements were carried out with a SHIMADZU DTG-60H. AFM measurements were carried out with SPI4000 and SPA300HV systems (Seiko Instruments Inc.). Absorption spectra were obtained on a UV-2550 UV−vis spectrophotometer (SHIMADZU). Dichroic measurements on a quartz waveguide were performed with a SIS-50 BS surface/ interface spectrometer (System Instruments). The thickness of the waveguide was 0.2 mm. Sample Preparation. Dispersion Sample for Absorption Measurements. The samples for absorption spectra were prepared as follows. Clay (SSA)−porphyrin complexes were prepared by mixing the aqueous SSA solution and the aqueous

Figure 2. Experimental setup of the surface−interface spectrometer with a quartz waveguide. In the orientational control experiments, the sample was covered with solvent.

3. RESULTS & DISCUSSION Adsorption Orientation of cis-DPyP in Water and in Water−Organic Solvent Mixture. The λmax of the porphyrin Soret band on the clay surface in water was 455 nm, whereas that in water in the absence of clay was 419 nm. The λmax shifting on adsorption to the clay surface has been shown to mainly depend on the flattening of the meso-substituted conjugative groups so that they are coplanar with the porphyrin ring,54−56 and the aggregation behavior was completely 9246



Article

negligible in the present system.41,42 The flattening induces more extensive delocalization of π-electrons over the molecular plane including the meso-substituted aromatic groups, where the electron-withdrawing pyridinium groups enhance the πelectron delocalization and lead to the red shift in λmax. The parallel adsorption of cis-DPyP on the clay surface in water was confirmed by a dichroic measurement on the waveguide.44,47 According to quantum chemical calculations, it is expected that the dihedral angle between the porphyrin ring and the peripheral aromatic ring affects the λmax of the porphyrin.45,46,54 When the porphyrin adsorbs on the clay surface with a perpendicular orientation, the λmax of the porphyrin should shift to 419 nm due to molecular flattening relaxation. The effect of solvent composition changes on porphyrin orientation was observed by changes in the absorption spectra. Under these conditions, the solution maintained complete transparency. The absorption spectra of the clay−porphyrin complex were measured in organic solvent/water mixtures (90/ 10 (v/v)) mixtures (Figure 3). As the content of DMF

Figure 4. Schematic view of the orientation of cis-DPyP on the nanolayered compound surface with changes in solvent composition.

To determine the orientational angle for each species, a dichroic measurement on the waveguide was carried out under each solvent composition. The detailed procedures to measure the dichroic spectra of cis-DPyP on the clay surface are described in the Experimental Section and in previous reports.44,47 The absorption spectra of the cis-DPyP−clay complex on the quartz waveguide covered with water and DMF were measured with s- and p-polarized light. The dichroic spectra of the cis-DPyP−clay complex in DMF/water = 0/100 and 90/10 (v/v) are shown in Figure 5. In DMF/water = 90/ 10, with s-polarized light, a weaker absorption at 425 nm was observed. With p-polarized light, a stronger absorption at 425 nm was observed. The dichroic ratio (Absp/Abss) was 1.23. The tilt angle of cis-DPyP versus the clay surface was determined to be 68° by the quantitative analysis.45 In DMF/ water = 0/100, the tilt angle of cis-DPyP was determined to be less than 5°. Thus, we can conclude that a drastic change in tilt angle of cis-DPyP on the clay surface takes place between species P and T.

Figure 3. Absorption spectra of cis-DPyP in DMF/water (0/100 to 97/3 (v/v)).

increased, the λmax of the porphyrin shifted to shorter wavelength. The shifting of λmax to shorter wavelength indicates π-electron relocalization. There are two possibilities for the hypsochromic shift: (i) a change of orientational angle of the porphyrin to the clay surface, which induces relaxation of the porphyrin flattening; and (ii) desorption of porphyrin from the clay surface. To rule out the possibility of desorption of porphyrin, centrifugation and filtration of the clay−porphyrin complex were carried out. In the supernatant and filtrate respectively no porphyrin was detected by absorption spectroscopy. These observations clearly indicate that the porphyrin molecule changes its orientation on the clay surface with the change of solvent composition. This means that the addition of DMF changes the porphyrin orientation from parallel to tilted, thereby decreasing the porphyrin flattening, which leads to the shift of λmax to shorter wavelength. When the DMF content increased, the species P (parallel) at 455 nm decreased, and the species T (tilted) at 424 nm increased, with an isosbestic point at 444 nm although the isosbectic point was blurred slightly owing to the solvent effect. This spectral change indicates a two-level orientation change as shown in Figure 4. The parallel species and the tilted species are in equilibrium. Each spectrum can be well expressed by the linear sum of species P and species T. The tilting behavior of cis-DPyP on the clay surface is depicted in Figure 4.

Figure 5. Absorption spectra of cis-DPyP with s and p wave light on the quartz waveguide covered with water/DMF mixtures (DMF/water mixtures (DMF/water (v/v) = 0/100 (a), 90/10 (b)).

Thermodynamic Study of Changes in Porphyrin Orientation on the Clay Surface. To understand and thus learn to control the porphyrin orientation on the clay surface, a thermodynamic study was carried out. A temperature effect on the equilibrium between species P and T was observed. The absorption spectra of the cis-DPyP−clay complex measured in DMF/water = 60/40 (v/v) at 283, 293, 303, 313, 323, and 333 K are shown in Figure 6. As the temperature increased, species P (455 nm) increased and species T (424 nm) decreased. This process was not affected by temperature hysteresis. The concentration ratio of species P and T at each temperature was determined by spectral fitting. Each absorption spectrum was well fitted with a linear combination of absorption spectra of species P and T. The ratios at each temperature of T and P were shown in Figure 6. Thus, the equilibrium constant K (= [T]/[P]) at each temperature was determined. The van’t Hoff type plot is shown in Figure 7. The obtained plot can be analyzed by a straight line. According to eq 1, ΔH and ΔS can be determined from the slope and intercept of the plot. 9247



Article

Table 1. Summary of Thermodynamic Parameters on Porphyrin Orientation Change on the Clay Surface in DMF/ water = 60/40 (v/v)

a

ΔH/kJmol−1

ΔS/JK−1 mol−1

ΔG/kJmol−1a

−25.8

−77.6

−2.5

The values are at 300 K.

Table 2. Solvent Effect on λmax x of Porphyrin/SSA Complexa

Figure 6. Absorption spectra of the cis-DPyP−clay complex in DMF/ water (60/40) at 283, 293, 303, 313, 323, and 333 K.

ln K = ln

[T ] k ΔS ΔH = ln −1 = − [P] R RT k

aprotic solventb

λmax/nm

protic solventb

λmax/nm

1,4-dioxane THF acetone MeCN DMF DMSO pyridine

430 424 423 424 426 424 430

2-propanol EtOH MeOH 100% water

459 461 461 455

[SSA] = 2.0 × 10−5 eq L−1. Porphyrin loading level is 5.0% vs CEC of the clay. bSolvent/water (90/10 (v/v)). a

(1)

The calculated thermodynamic parameters from the van’t Hoff plot are summarized in Table 1. The both value of ΔH and ΔS in the reorientation from species P to species T are negative. Thus, we can conclude that species P is stabilized by the ΔS term, and species T is stabilized by the ΔH term. We have determined the thermodynamic parameters also in the case of DMF/water (v/v) = 70/30. The value of ΔH, ΔS, and ΔG are −29.4 kJmol−1, −77.2 JK−1mol−1, and −6.2 kJmol−1. As expected, the decrease of water content led to the decrease of ΔH that indicates the increase of electrostatic interactions. Effect of Different Organic Solvents on Porphyrin Orientational Behavior. To discuss the factors determining the ΔS value, the effects of different organic solvents on porphyrin orientation on the clay surface were examined. 1,4dioxane, tetrahydrofuran, acetone, acetonitrile, DMF, DMSO, pyridine, methanol, ethanol, and 2-propanol were adopted as water-miscible organic solvents. The λmax values of cis-DPyP in the clay complex in water/organic solvent mixtures (10/90 (v/ v)) are summarized in Table 2. Water (10% v/v) was added for adequate dispersion of clay sheets. The λmax values in protic solvents were around 460 nm, which indicates that the porphyrin molecule adsorbs on the clay surface in a parallel orientation. However, the values in aprotic solvents were around 425 nm, which indicates that the porphyrin molecule

adsorbs on the clay surface in a tilted orientation. These results suggest that the hydrogen bonding ability of the solvent should play some role in determining the porphyrin orientation. To examine the solvent effect on the porphyrin orientation, a quantitative analysis of the solvent effect was carried out. The λmax value of the porphyrin was plotted versus the volume fraction of organic solvent in water as shown in Figure 8.

Figure 8. Porphyrin λmax for various contents of organic solvent in water.

Figure 7. (a) Equilibrium between parallel and tilted orientation. (b) van’t Hoff plot of the cis-DPyP−clay complex in DMF/water mixtures (DMF/ water (v/v) = 60/40). 9248



Article

of such icebergs decreases the entropy of the system. To avoid the decrease of entropy, the hydrophobic surfaces tend to face each other in order to decrease their total surface area facing the solvent. Thus, a hydrophobic interaction, which is derived from the entropy term, would play an important role in protic solvents. The hydrophobic interaction makes the parallel orientation of the porphyrin stable compared to the tilted orientation. However, a hydrophobic interaction would not be effective in aprotic solvents. The results of the thermodynamic study and the strong correlation between the hydrogen bonding character of the solvent and the porphyrin orientation support the idea that a hydrophobic interaction plays an important role in the orientational change behavior of the porphyrin on the clay surface. Our interpretation suggests that the clay surface is sufficiently hydrophobic to induce a hydrophobic interaction. It is concluded that (i) the cationic pyridinium substituents of the porphyrin adsorb on the clay surface with electrostatic interactions, and the neutral phenyl portion of the porphyrin adsorbs on the clay surface, favored by a hydrophobic interaction that stabilizes the entropic energy term in protic solvents, and (ii) in aprotic solvents, the enthalpy term, which is mainly due to the electrostatic interaction between porphyrin and clay, and interactions between solvent molecule and clay/ porphyrin surfaces, stabilizes the tilted porphyrin orientation on the clay surface.

Although the porphyrin in the complex exhibited a spectral shift to shorter wavelength with increasing content of organic solvent, the points at which the orientational change occurred, defined as the content inducing the drastic λmax change, were different in different solvents. At OCP, the absorbance of [T] is nearly equal to that of [P]. The orientational change point (OCP) for acetone is shown with an arrow in Figure 8. In this case, OCP is 58%. A low OCP indicates that the solvent induces the porphyrin orientational change easily. The relationship between solvent parameters such as relative dielectric constant and dipole moment, and the OCP are shown in Figure 9. There is no apparent correlation between

Figure 9. Relationships between dielectric constant (left) and dipole moment (right), and the orientational change point.

either relative dielectric constant or dipole moment and the OCP. Other solvent parameters such as acceptor number and donor number also exhibited no correlation. The relationship between Hansen’s solubility parameters57 and the OCP are shown in Figure 10. Among various solvent parameters, only the hydrogen bonding parameter exhibits a good correlation with the OCP. As the hydrogen bonding parameter decreased, the OCP decreased. It is apparent that hydrogen bonding plays an important role in the porphyrin orientation. The tilted porphyrin orientation is more stable in solvents with lower hydrogen bonding parameters. In the case of protic solvents, a solvent iceberg network58 should form hydrogen bonding network on hydrophobic surfaces of the complex formed by porphyrin aromatic rings and clay. The clay such as SSA consists of two tetrahedral silicate layers, which hold an octahedral alumina layer between of them. The clay surface is thought to be hydrophobic because there are no dangling bonds at oxygen because each apex oxygen atoms is shared by two tetrahedral silicates at the surface of the clay. In fact, it is known that talc which has very low charge density is completely hydrophobic. The formation

4. CONCLUSIONS The adsorption orientational changes of cationic porphyrins on a synthetic clay surface were examined as a function of temperature and solvents. The orientation of the porphyrin on the clay surface was studied by absorption spectra and dichroic absorption spectra using evanescent light on the waveguide. These experiments showed that the porphyrin orientation could be controlled by solvent composition. Whereas parallel orientation with respect to the clay surface was stable in protic solvents, a tilted orientation was stable in aprotic solvents. Because an orientation change of the porphyrin induces a very large absorption spectral shift (∼30 nm), this orientation change behavior is, in fact, an example of solvatochromism. Thermodynamic parameters for the orientation change were obtained in water/DMF mixtures (DMF/water (v/v) = 60/40). We conclude that the balance of entropy, which is mainly due to a hydrophobic interaction, and enthalpy, which is mainly due to electrostatic interactions, determines the stability in the corresponding conditions.

Figure 10. Relationships between solvent characters and the orientational change point: (A) diffusion term [D]; (B) polarity term [P]; (C) hydrogen bonding term [H]. 9249



■

Article

(17) Kunitake, M.; Batina, N.; Itaya, K. Self-Organized Porphyrin Array on Iodine-Modified Au (111) in Electrolyte Solutions: In Situ Scanning Tunneling Microscopy Study. Langmuir 1995, 11, 2337− 2340. (18) Lei, S. B.; Wang, C.; Yin, S. X.; Wang, H. N.; Xi, F.; Liu, H. W.; Xu, B.; Wan, L. J.; Bai, C. L. Surface Stabilized Porphyrin and Phthalocyanine Two-Dimensional Network Connected by Hydrogen Bonds. J. Phys. Chem. B 2001, 105, 10838−10841. (19) Yokoyama, T.; Yokoyama, S.; Kamikado, T.; Okuno, Y.; Mashiko, S. Selective Assembly on a Surface of Supramolecular Aggregates with Controlled Size and Shape. Nature 2001, 413, 619− 621. (20) van den Bruele, F. J.; Elemans, J. A. A. W.; Rowan, A. E.; van Enckevort, W. J. P.; Vlieg, E. Self-Assembly of Porphyrins on a Single Crystalline Organic Substrate. Langmuir 2010, 26, 498−503. (21) Haq, S.; Hanke, F.; Dyer, M. S.; Persson, M.; Iavicoli, P.; Amabilio, D. B.; Raval, R. Clean Coupling of Unfunctionalized Porphyrin at Surfaces to Give Highly Oriented Organometallic Oligomers. J. Am. Chem. Soc. 2011, 133, 12031−12039. (22) Friesen, B. A.; Wiggins, B.; McHale, J. L.; Mazur, U.; Hipps, K. W. A Self-Assembled Two-Dimensional Zwitterionic Structure: H6TSPP Studied on Graphite. J. Phys. Chem. C 2011, 115, 3990−3999. (23) Ogawa, M.; Kuroda, K. Photofunctions of Intercalation Compounds. Chem. Rev. 1995, 95, 399−438. (24) Takagi, K.; Shichi, T. In Solid State and Surface Photochemistry; Marcel Dekker: New York, 2000; Vol. 5, p 31. (25) Shichi, T.; Takagi, K. Clay Minerals as Photochemical Reaction Fields. J. Photochem. Photobiol. C 2000, 1, 113−130. (26) Takagi, S.; Eguchi, M.; Tryk, D. A.; Inoue, H. Porphyrin Photochemistry in Inorganic/Organic Hybrid Materials: Clays, Layered Semiconductors, Nanotubes, and Mesoporous Materials. J. Photochem. Photobiol. C 2006, 7, 104−126. (27) Jacobs, K. Y.; Schoonheydt, R. A. Time Dependence of the Spectra of Methylene Blue-Clay Mineral Suspensions. Langmuir 2001, 17, 5150−5155. (28) Gessner, F.; Schmitt, C. C.; Neumann, M. G. Time-Dependent Spectrophotometric Study of the Interaction of Basic Dyes with Clays. I. Methylene Blue and Neutral Red on Montmorillonite and Hectorite. Langmuir 1994, 10, 3749−3753. (29) Bujdak, J.; Iyi, N.; Fujita, T. The Aggregation of Methylene Blue in Montmorillonite Dispersions. Clay Miner. 2002, 37, 121−133. (30) Yamagishi, A.; Soma, M. Optical Resolution of Metal Chelates by Use of Adsorption on a Colloidal Clay. J. Am. Chem. Soc. 1981, 103, 4640−4642. (31) Tanigichi, M.; Kaneyoshi, M.; Nakamura, Y.; Yamagishi, A.; Iwamoto, T. A Stopped-Flow Electric Dichroism Study on Adsorption of Metal Chelates by a Colloidal Clay. J. Phys. Chem. 1990, 94, 5896− 5900. (32) Yamagishi, A. Stereoselective Adsorption on a Clay Surface Modified by an Optically Active Nickel(II) Tris(1,10-Phenanthroline) Chelate. J. Chem. Soc., Chem. Commun. 1981, 1128−1129. (33) Czimerova, A.; Bujdak, J.; Gasplovsky, A. The Aggregation of Thionine and Methylene Blue Dye in Smectite Dispersion. Colloids Surf., A 2004, 243, 89−96. (34) Hideo Hata, H.; Kobayashi, Y.; Mallouk, T. E. Encapsulation of Anionic Dye Molecules by a Swelling Fluoromica through Intercalation of Cationic Polyelectrolytes. Chem. Mater. 2007, 19, 79−87. (35) Czimerova, A.; Jankovic, L.; Bujdak, J. Effect of the Exchangeable Cations on the Spectral Properties of Methylene Blue in Clay Dispersions. J. Colloid Interface Sci. 2004, 274, 126−132. (36) Kaneko, Y.; Iyi, N.; Bujdak, J.; Sasai, R.; Fujita, T. Effect of Layer Charge Density on Orientation and Aggregation of a Cationic Laser Dye Incorporated in the Interlayer Space of Montmorillonites. J. Colloid Interface Sci. 2004, 269, 22−25. (37) Umemura, Y.; Einaga, Y.; Yamagishi, A. Formation of a Stable Thin Sheet of Prussian Blue in a Clay-Organic Hybrid Film. Mater. Lett. 2004, 58, 2472−2475.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (S. T.), inoue-haruo@tmu. ac.jp (H. I.); fax: +80-426-53-3416. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS

■

REFERENCES

This work has been partly supported by a Grant-in-Aid for Precursory Research for Embryonic Science and Technology (PRESTO) from the Japan Science and Technology Agency (JST), and JSPS Research Fellow DC1 from Japan Society for the Promotion of Science.

(1) Aviram, A.; Rantner, M. A. Molecular Rectifiers. Chem. Phys. Lett. 1974, 29, 277−283. (2) Joachim, C.; Gimzewski, J. J.; Aviram, A. Electronics Using Hybrid-Molecular and Mono-molecular Devices. Nature 2000, 408, 541−548. (3) Lehn, J.-M. Cryptates: Inclusion Complexes of Macropolycyclic Recepter Molecules. Pure Appl. Chem. 1978, 50, 871−892. (4) The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic Press: New York, 1999. (5) Takagi, S.; Inoue, H. In Multimetallic and Macromolecular Inorganic Photochemistry; Ramamurthy, V., Schanze, K. S., Eds.; Marcel Dekker: New York, 1999; Vol. 6, p 215. (6) Prokhorenko, V. I.; Holzwarth, A. R.; Muller, M. G.; Schaffner, K.; Miyatake, T.; Tamiaki, H. Energy Transfer in Supramolecular Artificial Antennae Units of Synthetic Zinc Chlorins and CoAggregated Energy Traps. A Time-Resolved Fluorescence Study. J. Phys. Chem. B 2002, 106, 5761−5768. (7) Miyatake, T.; Tamiaki; Holzwarth, A. R.; Schaffner, K. Artificial Light-Harvesting Antennae: Singlet Excitation Energy Transfer from Zinc Chlorin Aggregate to Bacteriochlorin in Homogeneous Hexane Solution. Photochem. Photobiol. 1999, 69, 448−456. (8) Takahashi, R.; Kobuke, Y. Hexameric Macroring of GablePorphyrins as a Light-Harvesting Antenna Mimic. J. Am. Chem. Soc. 2003, 125, 2372−2373. (9) Yonehara, H.; Ogawa, K.; Pac, C. Kokagaku 1995, 19, 21−28. (10) Escudero, C.; Crusats, J.; Diez-Perez, I.; El-Hachemi, Z.; Ribo, J. M. Folding and Hydrodynamic Forces in J-Aggregates of 5-Phenyl10,15,20-Tris-(4-Sulfophenyl)Porphyrin. Angew. Chem., Int. Ed. 2006, 45, 8032−8035. (11) Aratani, N.; Osuka, A.; Cho, H. S.; Kim, D. Photochemistry of Covalently-Linked Multi-Porphyrinic Systems. J. Photochem. Photobiol., C 2002, 3, 25−52. (12) Imahori, H.; Norieda, H.; Yamada, H.; Nishimura, Y.; Yamazaki, I.; Sakata, Y.; Fukuzumi, S. Light-Harvesting and Photocurrent Generation by Gold Electrodes Modified with Mixed Self-Assembled Monolayers of Boron−Dipyrrin and Ferrocene−Porphyrin−Fullerene Triad. J. Am. Chem. Soc. 2001, 123, 100−110. (13) Miller, M. A.; Lammi, R. K.; Prathapan, S.; Holten, D.; Lindsey, J. S. A Tightly Coupled Linear Array of Perylene, Bis (Porphyrin), and Phthalocyanine Units that Functions as a Photoinduced EnergyTransfer Cascade. J. Org. Chem. 2000, 65, 6634−6649. (14) Choi, M.-S.; Aida, T.; Yamazaki, T.; Yamazaki, I. Dendritic Multiporphyrin Arrays as Light-Harvesting Antennae: Effects of Generation Number and Morphology on Intramolecular Energy Transfer. Chem.-Eur. J. 2002, 8, 2667−2678. (15) Gilat, S. L.; Adronov, A.; Frechet, J. M. Light Harvesting and Energy Transfer in Novel Convergently Constructed Dendrimers. Angew. Chem. Int. Ed. 1999, 38, 1422−1427. (16) Bar-Haim, A.; Klafter, J.; Kopelman, R. Dendrimerd as Controlled Artificial Energy Antennae. J. Am. Chem. Soc. 1997, 119, 6197−6198. 9250



Article

Strong Host-Guest Interaction due to the “Size-Matching Rule. J. Phys. Chem. C 2012, 116, 7879−7885. (57) Beerbower, A.; Jensen, W. B. The HSAB Principle and Extended Solubility Theory. Inorg. Chim. Acta 1983, 75, 193−197. (58) Frank, H. S.; Evans, M. W. Free Volume and Entropy in Condensed Systems III. Entropy in Binary Liquid Mixtures; Partial Molal Entropy in Dilute Solutions; Structure and Thermodynamics in Aqueous Electrolytes. J. Chem. Phys. 1945, 13, 507−532.

(38) Sumitani, M.; Takagi, S.; Tanamura, Y.; Inoue, H. Oxygen Indicator Composed of an Organic/Inorganic Hybrid Compound of Methylene Blue, Reductant, Surfactant and Saponite. Anal. Sci. 2004, 20, 1153−1157. (39) Okada, T.; Watanabe, Y.; Ogawa, M. Photoregulation of the Intercalation Behavior of Phenol for Azobenzene-Clay Intercalation Compounds. J. Mater. Chem. 2005, 15, 987−992. (40) Sasai, R.; Iyi, N.; Fujita, T.; Arbeloa, F. L.; Martines, V. M.; Takagi, K.; Ito, H. Luminescence Properties of Rhodamine 6G Intercalated in Surfactant/Clay Hybrid Thin Solid Films. Langmuir 2004, 20, 4715−4719. (41) Takagi, S.; Shimada, T.; Yui, T.; Inoue, H. High Density Adsorption of porphyrin onto Clay Layer without Aggregation: Characterization of Smectite-Cationic Porphyrin Complex. Chem. Lett. 2001, 30, 128−129. (42) Takagi, S.; Shimada, T.; Eguchi, M.; Yui, T.; Yoshida, H.; Tryk, D. A.; Inoue, H. High-Density Adsorption of Cationic Porphyrins on Clay Layer Surfaces without Aggregation: The size-Matching Effect. Langmuir 2002, 18, 2265−2272. (43) Takagi, S.; Tryk, D. A.; Inoue, H. Photochemical Energy Transfer of Cationic Porphyrin Complexes on Clay Surface. J. Phys. Chem. B 2002, 106, 5455−5460. (44) Eguchi, M.; Takagi, S.; Tachibana, H.; Inoue, H. The ‘Size Matching Rule’ in Di-, Tri-, and Tetra-Cationic Charged Porphyrins/ Synthetic Clay Complexes: Effect of the Inter-Charge Distance and the Number of Charged Sites. J. Phys. Chem. Solids 2004, 65, 403−407. (45) Eguchi, M.; Tachibana, H.; Takagi, S.; Tryk, D. A.; Inoue, H. Dichroic Measurements on Dicationic and Tetracationic Porphyrins on Clay Surfaces with Visible-Light-Attenuated Total Reflectance. Bull. Chem. Soc. Jpn. 2007, 80, 1350−1356. (46) Eguchi, M.; Tachibana, H.; Takagi, S.; Inoue, H. Microscopic Structures of Adsorbed Cationic Porphyrins on Clay Surfaces: Molecular Alignment in Artificial Light-Harvesting Systems. Res. Chem. Intermed. 2007, 33, 191−200. (47) Eguchi, M.; Takagi, S.; Inoue, H. The Orientation Control of Dicationic Porphyrins on Clay Surfaces by Solvent Polarity. Chem. Lett. 2006, 35, 14−15. (48) Takagi, S.; Eguchi, M.; Inoue, H. Light-Harvesting Energy Transfer and Subsequent Electron Transfer of Cationic Porphyrin Complexes on Clay Surfaces. Langmuir 2006, 22, 1406−1408. (49) Shiragami, T.; Nabeshima, K.; Yasuda, M.; Inoue, H. Roles of Axial Ligands on Intercalation of Cationic Metalloporphyrin into Smectite Clay Layers. Chem. Lett. 2003, 32, 148−149. (50) Shiragami, T.; Nabeshima, K.; Matsumoto, J.; Yasuda, M.; Inoue, H. Non-Aggregated Intercalation of Dicationic Tetraphenylporphyrinatoantimony(V) Complexes into Smectite Clay Layers. Chem. Lett. 2003, 32, 484−485. (51) Takagi, S.; Eguchi, M.; Yui, T.; Inoue, H. Photochemical Electron Transfer Reactions in Clay-Porphyrin Complexes. Clay Sci. 2006, 12 (Supplement2), 82−87. (52) Shiragami, T.; Nabeshima, K.; Matsumoto, J.; Takagi, S.; Inoue, H.; Yasuda, M. Effects of Axial Ligands on the Formation of a Layered Structure in Mono- and Di-Cationic Charged Tetraphenylporphyrinatoantimony(V)/Synthetic Clay Composites. Bull. Chem. Soc. Jpn. 2005, 78, 2251−2258. (53) Shiragami, T.; Mori, Y.; Matsumoto, J.; Takagi, S.; Inoue, H.; Yasuda, M. Non-Aggregated Adsorption of Cationic Metalloporphyrin Dyes onto Nano-Clay Sheets Films. Colloids Surf., A 2006, 284−285, 284−289. (54) Chernia, Z.; Gill, D. Flattening of TMPyP Adsorbed on Laponite. Evidence in Observed and Calculated UV-vis Spectra. Langmuir 1999, 15, 1625−1633. (55) Kuykendall, V. G.; Thomas, J. K. Photophysical Investigation of the Degree of Dispersion of Aqueous Colloidal Clay. Langmuir 1990, 6, 1350−1356. (56) Ishida, A.; Masui, D.; Shimada, T.; Tachibana, H.; Inoue, H.; Takagi, S. The Mechanism of the Porphyrin Spectral Shift on Inorganic Nanosheets: The Molecular Flattening Induced by the 9251


Role of Hydrophobic Interaction in Controlling the Orientation of

Recommend Documents