Adsorption and Aggregation of a Cationic Cyanine Dye on Smectites

of aqueous dye solutions by low cost adsorbents. Rashmi Sanghi , Bani Bhattacharya. Coloration Technology 2002 118 (10.1111/cte.2002.118.issue-5),...
0 downloads 0 Views 258KB Size
Download PDF
16218

J. Phys. Chem. 1996, 100, 16218-16221

Adsorption and Aggregation of a Cationic Cyanine Dye on Smectites Makoto Ogawa,*,†,‡ Ryo Kawai,§ and Kazuyuki Kuroda§,⊥ The Institute of Physical and Chemical Research (RIKEN), Hirosawa 2-1, Wako-shi, Saitama 351-01, Japan; Department of Applied Chemistry, Waseda UniVersity, Ohkubo-3, Shinjuku-ku, Tokyo 169, Japan; and Kagami Memorial Laboratory for Materials Science and Technology, Waseda UniVersity, Nishiwaseda 2-8-26, Shinjuku-ku, Tokyo 169, Japan ReceiVed: January 24, 1996; In Final Form: July 5, 1996X

The adsorption and aggregate formation of a cationic cyanine dye, 1,1′-diethyl-2,2′-cyanine, on montmorillonite and saponite have been investigated for aqueous suspensions and cast films. In aqueous suspensions, the cyanine dye cations formed J-aggregates on montmorillonite, while they distribute molecularly on saponite. On the other hand, the dye formed J-aggregates on both montmorillonite and saponite in the cast films. Thus, the spectroscopic features of the cyanine dye reflected the difference between montmorillonite and saponite in organizing guest species. This difference suggests that the cyanine dye can be organized in a controlled manner by the selection of host materials. The J-aggregates formed on the layered silicates may be useful for the study of optical properties of the aggregates because of their stable and confined microstructure.

Introduction

SCHEME 1

Construction of ordered molecular assembly is a current topic from a wide range of scientific and practical viewpoints.1 Intercalation of guest species into layered inorganic solids is a way to produce ordered inorganic-organic assemblies with unique microstructures controlled by host-guest and guestguest interactions.2 Among possible layered solids, the smectite group of layered clay minerals provides attractive features such as the large surface area, the swelling behavior, and the ion exchange properties in organizing organic guest species.3,4 The organization of photoactive species on the silicate surfaces is a way to construct novel photofunctional supramolecular systems.5,6 It has been reported that the adsorbed states of guest species on the silicate surfaces are controlled by the layer charge density, the type of isomorphous substitution,7 and coadsorption of photoinactive species.8 Since the characteristics of the photoprocesses are sensitive to the environment where the photoactive species are adsorbed, various important information on the nature and the microstructures of the host-guest systems have been clarified by such studies. In this study, we investigated the adsorption of a cationic cyanine dye, 1,1′-diethyl-2,2′-cyanine (pseudoisocyanine; abbreviated as PIC, whose molecular structure is shown in Scheme 1), on smectites (montmorillonite and saponite). We found an important difference in the states of the adsorbed cyanine dye on montmorillonite and synthetic saponite in aqueous suspensions and cast films. It is well-known that the spectral properties of cyanine dyes are strongly affected by the aggregation.9,10 These aggregates (so called J- and H-aggregates) have attracted much attention for the spectral sensitization of photographic processes11 and useful optical properties.12 The organization of cyanine dyes on silver halides,13 surfactant aggregates,14 colloidal silica,15 and polyelectrolytes16 has been investigated so far to understand the structure and the properties of the dye * To whom correspondence should be addressed. † RIKEN. ‡ Present address: PRESTO, JRDC and Institute of Earth Science, Waseda University, Nishiwaseda 1-6-1, Shinjuku-ku, Tokyo 169-50, Japan. § Department of Applied Chemistry, Waseda University. ⊥ Kagami Memorial Laboratory for Materials Science and Technology, Waseda University. X Abstract published in AdVance ACS Abstracts, September 1, 1996.

S0022-3654(96)00261-4 CCC: $12.00

aggregates. The organization of the cyanine dye and their spectroscopic features are expected to give new information on the nature of the present host-guest systems. Experimental Section Materials. Sodium-saponite (Sumecton SA supplied from Kunimine Industries Co., synthesized by a hydrothermal reaction) and sodium-montmorillonite (Kunipia F, Kunimine Industries Co.; Reference Clay Sample of The Clay Science Society of Japan) were used as the host materials. The cation exchange capacities of Na-saponite and Na-montmorillonite are 70 and 119 mequiv/100 g of host, respectively. PICBr was purchased from Nippon Kanko Shikiso Co. Sample Preparation. By addition of an aqueous suspension of montmorillonite into an aqueous solution of PICBr (with the final concentration of 5 × 10-6 M), a stable aqueous suspension was obtained. The amount of PIC cation in this mixture was 2.5 mmol/100 g of montmorillonite, which was much smaller than the cation exchange capacity of the montmorillonite. Consequently, most sodium ions remained unexchanged, so that the suspension was very stable without flocculation. The relative amounts of PICBr to host varied from 2.5 mmol/100 g of host to 50 mmol/100 g of host. The clay particles tend to flocculate at higher loading amount of PIC to the host, so that the spectra of the suspensions were recorded immediately after the magnetic stirring. Thin films were prepared by casting the aqueous mixtures on a glass substrate and dried in air at room temperature. Sodium-saponite was also used as the host material. Characterization. Absorption spectra of the suspensions and the cast films were recorded on a Shimadzu UV-3100PC spectrophotometer. Fluorescence spectra were recorded on a © 1996 American Chemical Society

Cationic Cyanine Dye on Smectites

Figure 1. Absorption spectra of the (a) 5 × 10-6 M PICBr aqueous solution and aqueous mixtures containing (b) 20, (c) 10, (d) 5, and (e) 1 mg of montmorillonite and 100 mL of 5 × 10-6 M PICBr aqueous solution.

Figure 2. Luminescence spectra of the aqueous mixtures containing (a) 20, (b) 10, (c) 5, and (d) 1 mg of montmorillonite and 100 mL of 5 × 10-6 M PICBr aqueous solution. The excitation wavelength is 520 nm.

Hitachi F-4500 spectrofluorophotometer. X-ray diffraction patterns of the cast films were recorded on a Mac Science MXP3 diffractometer with monochromatic Cu KR radiation. Results and Discussion The absorption spectrum of the aqueous mixture containing 20 mg of montmorillonite and 100 mL of 5 × 10-6 M PICBr aqueous solution (the amount of PIC is 2.5 mmol/100 g of montmorillonite) is shown in Figure 1b. (The absorption spectrum of a 5 × 10-6 M PICBr aqueous solution is shown in Figure 1a, in which the absorption band of monomeric PIC appeared at around 520 nm.) In the absorption spectrum, a new absorption band appeared at 567 nm which is red-shifted relative to the monomer absorption at 522 nm. The emission spectrum of the aqueous mixture is shown in Figure 2a. (The excitation wavelength is 520 nm.) The luminescence spectrum consists of an intense resonance band at around 570 nm. These absorption and luminescence bands are characteristic of Jaggregates of PIC.9,10 Thus, it was revealed that the PIC formed J-aggregates on the surface of montmorillonite in the aqueous mixture. Similar absorption and luminescence spectra were obtained for the aqueous mixtures containing different amounts of montmorillonite (10, 5, and 1 mg/100 mL of PICBr aqueous solution). The absorption and luminescence spectra are shown in Figures 1 and 2. The adsorption of the cyanine dye by

J. Phys. Chem., Vol. 100, No. 40, 1996 16219

Figure 3. Absorption spectra of the cast films prepared from the aqueous mixtures containing 100 mL of 5 × 10-6 M PICBr aqueous solution and 20 (a), 10 (b), 5 (c), and 1 mg (d) of montmorillonite.

montmorillonite, which is probably by the mechanism of cation exchange, gives rise to a red shift of the 522 nm band to 567 nm. This great shift indicates the formation of Jaggregates of PIC on the silicate surfaces irrespective of the loading amount of PIC. It was thought that the guest-guest interactions between the dye ions led to the aggregated states even at the low amount of the dyes on the silicate surfaces. Similar aggregation behavior has been observed for the tris(2,2′-bipyridine)ruthenium(II) complex ions adsorbed on the smectites.5,6,17 The distribution of the negative charge on the silicate surfaces, the size of tris(2,2′-bipyridine)ruthenium(II) complex ion, and the guest-guest interactions are thought to play a dominant role for the aggregation. The aqueous suspensions are stable when the loading amount of PIC is low, while they tend to flocculate when the degree of saturation is high. As a result of flocculation, the PIC cation may form an aggregate at interparticle space. The absorbance decreases with decreasing concentration of montmorillonite, showing that the silicate particles flocculate when the loading amounts of PIC are relatively high. In order to understand the adsorption behavior of PIC on the silicates further, thin films were prepared by casting the aqueous mixtures on a glass substrate. The absorption spectra of the films are shown in Figure 3. The absorption spectrum of the film prepared from the aqueous mixture containing 20 mg of montmorillonite and 100 mL of 5 × 10-6 M PICBr aqueous solution (Figure 3a) showed the absorption band characteristic of monomeric PIC at around 520 nm together with minor J-band while that (Figure 1b) of the aqueous suspension showed the presence of J-aggregates. The X-ray diffraction pattern of the cast film is shown in Figure 4a. The basal spacing of the film is ca. 1.3 nm, showing the interlayer spacing of ca. 0.3 nm. This value indicates that the PIC cations distribute on the external surface of the silicate, or they form monolayer with their molecular planes parallel to the silicates sheets. In the aqueous mixture, the adsorbed PIC cations are mobile and cluster to form J-aggregates through guest-guest interactions on the silicate surfaces. These observations indicate that the arrangement of the adsorbed PIC cations on the silicate surface changed with evaporation of solvents from the J-aggregated state to a monomeric state. The amount of PIC cations is 2.5 mmol/ 100 g of montmorillonite in this system. Such a small amount of PIC cations can be adsorbed on the silicate surface without aggregation in the cast film.

16220 J. Phys. Chem., Vol. 100, No. 40, 1996

Figure 4. X-ray diffraction patterns of the cast films prepared from the aqueous mixtures containing 100 mL of 5 × 10-6 M PICBr aqueous solution and 20 (a), 5 (b), and 1 mg (c) of montmorillonite.

Small red shifts of π-π* absorption have been observed upon adsorption of the cationic dyes on smectites.7,11 These bathochromic shifts have been attributed to the increased polar environment of the interlayer space compared with water. In the present system, the absorption band red-shifted slightly (from 522 to 524 nm) upon adsorption on montmorillonite, suggesting that the possible interactions between the silicate layers and PIC cations. During the drying, the contact between the aromatic rings of PIC and the oxygen plane of silicate layer were thought to become more significant, resulting in the interactions between the oxygen plane and the PIC. On the other hand, the absorption spectrum (Figure 3d) of the film prepared from the aqueous mixture containing 1 mg of montmorillonite and 100 mL of 5 × 10-6 M PICBr aqueous solution showed an absorption band at 568 nm which is characteristic of the J-aggregate of PIC. In this case, the amount of PIC cations is 50 mmol/100 g of montmorillonite. The large amount of PIC cations was thought to be forced into close proximity in the interlayer space of montmorillonite. The XRD pattern is shown in Figure 4c. The d001 spacing of the cast film is 1.6 nm, which shows the interlayer spacing of ca. 0.6 nm, showing that the PIC cations form a monolayer in the interlayer space of montmorillonite with π interactions between adjacent dye cations to give J-aggregated state. The X-ray diffraction pattern and the absorption spectrum of the cast film prepared from the aqueous mixture containing 5 mg of montmorillonite and 100 mL of 5 × 10-6 M PICBr aqueous solution are shown in Figures 4b and 3c, respectively. At the loading level of PIC (10 mmol of PIC/100 g of montmorillonite), the absorption band due to the J-aggregate of PIC appeared in the absorption spectrum. The X-ray diffraction pattern showed the basal spacing of 1.3 nm, indicating that the adsorbed PIC cations cannot form J-aggregate in the interlayer space. These observations suggest that the PIC cations form J-like aggregate at the external surface of montmorillonite. The possibility that the expanded interlayer spacing cannot be detected by the X-ray diffraction pattern may be of concern. The absorption spectra of the cast films showed the absorption bands at around 490 and 520 nm ascribable to unassociated PIC monomers together with that of the Jaggregates at around 570 nm. These absorption spectra suggest the presence of unassociated PIC monomers and J-aggregated PIC on the cast films. Interestingly, the spectroscopic features of PIC were different when synthetic saponite was used. The absorption spectrum

Ogawa et al.

Figure 5. Absorption spectra of the aqueous mixture containing 100 mL of 5 × 10-6 M PICBr and 20 (a) and 1 mg (b) of saponite and those of the cast films prepared from the aqueous mixture containing 100 mL of 5 × 10-6 M PICBr and 20 (c) and 1 mg (d) of saponite.

of the aqueous mixtures containing 20 mg of saponite and 100 mL of 5 × 10-6 M PICBr aqueous solution is shown in Figure 5a. The absorption band due to monomeric PIC Br red-shifted slightly upon the addition of saponite, showing that the PIC cations distributed molecularly in the aqueous mixture with possible interaction with highly polar silicate layers. When the amount of saponite was changed (1 mg/100 mL corresponds to the 50 mmol of PIC/100 g of saponite) in the aqueous mixture, a shoulder appeared at 570 nm ascribable to the J-aggregate of PIC together with the absorption bands of monomeric PIC in the absorption spectrum (Figure 5b). However, the main bands in this spectrum were ascribable to the monomeric PIC, showing that only a part of PIC formed a J-aggregate. On the contrary, the cast films of PIC/saponite containing different amounts of PIC gave a result similar to that observed for PIC/montmorillonite system. The absorption spectra of the cast films prepared from the aqueous mixture of saponite and 5 × 10-6 M PICBr are also shown in Figure 5. When the amount of PICBr is 2.5 mmol/100 g of saponite, the absorption spectrum of the cast film (Figure 5c) showed the absence of J-aggregate of PIC. On the other hand, when the amount of PIC was increased to 50 mmol of PIC/100 g of saponite, the band due to monomeric PIC disappeared, and the J-band appeared at around 570 nm in the absorption spectrum of the cast film (Figure 5d). The basal spacings of the PIC/saponite films were ca. 1.3 and 1.7 nm for the compounds with 2.5 and 50 mmol of PIC/100 g of saponite, respectively. As suggested for the states of PIC cations adsorbed on montmorillonite in the cast films, the PIC cations distribute molecularly on the surface of saponite when the loading amount was low. The higher loading amount of dye resulted in the J-aggregated state of the PIC cations in the interlayer space of saponite. The relative contribution of 490 and 520 nm varied depending on the sample conditions. Since these bands do not show concentration dependence in aqueous solution, it is difficult to discuss the relative contribution of these two bands. The possible H-aggregation and dimerization on the silicate surfaces may be of concern. Thus, in the aqueous suspension, the adsorbed states of the cyanine dye varied depending on the layered silicates. On the contrary, the states of the cyanine dyes adsorbed on montmorillonite and saponite are similar in the cast films. This difference suggests that so-called “house of cards structure” of the silicate particles in the aqueous suspension is responsible for the states of PIC cation as has been reported for the adsorption and metachromasy of cationic dyes on laponite

Cationic Cyanine Dye on Smectites (synthetic hectorite).18 In the aqueous suspension, the adsorbed PIC cations distributed molecularly without aggregation on the colloidal particle of synthetic saponite. In the cast film, the silicate particles of synthetic saponite stacks to form an oriented aggregate, so that the adsorbed dye ions formed J-aggregates on the silicate surfaces. On the other hand, relatively large particles of montmorillonite offer an environment for the PIC cation to form the J-aggregate even in the aqueous suspension. The types of isomorphous substitution of the layered silicates, the octahedral substitution in montmorillonite, and the tetrahedral substitution in saponite may also be the reasons for the difference in the adsorption behavior of PIC cations. The J-aggregates formed on the layered silicates may be useful for the study of optical properties of the aggregates because of their stable and confined microstrutucre. Studies on the adsorption of cyanine dyes on various layered solids with different layer charge density and surface property are in progress and will be reported subsequently. Conclusion The adsorption and aggregate formation of PIC cations on montmorillonite and saponite have been investigated for aqueous suspensions and cast films. The spectroscopic features of the dye reflected the difference between montmorillonite and saponite in organizing guest species. This difference suggests that PIC cations can be organized in a controlled manner by using layered host materials as organizing media. The change in the state of adsorbed cyanine dyes during the evaporation of solvent has also been revealed. The J-aggregates formed on the layered silicates may be useful for the study of optical properties of the aggregates because of their stable and confined microstructure. Acknowledgment. This work was supported by a grant for “Special Researcher’s Basic Science Program” from the Science and Technology Agency of the Japanese Government and Grant-

J. Phys. Chem., Vol. 100, No. 40, 1996 16221 in-Aid for Scientific Research, from the Ministry of Education, Science and Culture of Japan. The authors are grateful to the referees for the helpful comments. References and Notes (1) Photochemistry in Organized & Constrained Media; Ramamurthy, V., Ed.; VCH Publishers: New York, 1991. (2) Intercalation Chemistry; Whittingham, M. S., Jacobson, A. J., Eds.; Academic Press: New York, 1982. (3) Theng, B. K. G. The Chemistry of Clay Organic Reactions; Adam Hilger: London, 1974. (4) Van Olphen,H. An Introduction to Clay Colloid Chemistry, 2nd ed.; Wiley-Interscience: New York, 1977. (5) Ogawa, M.; Kuroda, K. Chem. ReV. 1995, 95, 399. (6) Thomas, J. K. Acc. Chem. Res. 1988, 21, 275. (7) Cenes, J.; Schoonheydt, R. A. Clays Clay Miner. 1988, 36, 214. Grauer, Z.; Avnir, D.; Yariv, S. Can. J. Chem. 1984, 62, 1889. Grauer, Z.; Grauer, G. L.; Avnir, D.; Yariv, S. J. Chem. Soc., Faraday Trans. 11987, 83, 1685. Lo´pez Arbeloa, F.; Tapia Este´vez, M. J.; Lo´pez Arbeloa, T.; Lo´pez Arbeloa, I. Langmuir 1995, 11, 3211. (8) Ogawa, M.; Aono, T.; Kuroda, K.; Kato, C. Langmuir 1993, 9, 1529., Ogawa, M.; Inagaki, M.; Kodama, N.; Kuroda, K.; Kato, C. J. Phys.Chem. 1993, 97, 3819. Ogawa, M.; Handa, T.; Kuroda, K.; Kato, C.; Tani, T. J. Phys. Chem. 1992, 96, 8116. Usami, H.; Takagi, K.; Sawaki, Y. J. Chem. Soc., Faraday Trans. 1992, 88, 77. Tomioka, H.; Itoh, T. J. Chem. Soc., Chem. Commun. 1991, 532. (9) Jelley, E. E. Nature 1936, 138, 1009; 1937, 139, 631. (10) Scheibe, G. Angew. Chem. 1936, 49, 563. (11) Herz, A. H. AdV. Colloid Interface Sci. 1977, 8, 237. (12) Mo¨bius, D. AdV. Mater. 1995, 7, 437. (13) Muenter, A. A.; Brumbaugh, D. V.; Apolito, J.; Horn, L. A.; Spano, F. C.; Mukamel, S. J. Phys. Chem. 1992, 96, 2783. (14) Lehman, U. Thin Solid Films 1988, 160, 257. Sato, T.; Yonezawa, Y.; Hada, H. J. Phys. Chem. 1989, 93, 14. Nakashima, N.; Kunitake, T. J. Am. Chem. Soc. 1982, 104, 4261. (15) Quiteves, E. L.; Horng, M.-L.; Chen, S.-Y. J. Phys. Chem. 1988, 92, 256. (16) Horng, M. L.; Quiteves, E. L. J. Phys. Chem. 1993, 97, 12408. (17) Ghosh, P. K.; Bard, A. J. J. Phys.Chem. 1984, 88, 5519. Yamagishi, A. J. Coord. Chem. 1987, 16, 131. (18) For example: Yariv, S.; Nasser, A.; Bar-on, P. J. Chem. Soc., Faraday Trans. 1990, 86, 1593.

JP960261O