J . Phys. Chem. 1990, 94, 3766-3769
3766
of electronic structure over a surface and the association of different states with various surface defects and chemical contamination. These should be addressable by use of TS in the surface-scanning mode and are now under investigation. Acknowledgment. The support of this research by the Office
of Naval Research and the National Science Foundation (CHE8805865) is gratefully acknowledged. We appreciate the assistance of Dr. J. Kwak in the construction of the computer interface. Registry No. TiOz, 13463-67-7.
Aggregation of Azo Dyes Containing Pentafiuoroaniiine as a Diazo Component in Aqueous Solutions Kunihiro Hamada,*-+Toshiro Iijima,l Department of Polymer Science, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152, Japan
and Shigetoshi Amiya Central Research Laboratories, Kuraray Co. Ltd.. Sakazu 2045, Kurashiki 710, Japan (Received: September 29, 1989)
The aggregation of monoazo sulfonic dyes containing pentafluoroaniline as a diazo component in aqueous solutions was investigated by means of I9F NMR and electronic absorption spectroscopy. The five fluorine atoms attached to the benzene ring gave a NMR spectrum with one doublet and two triplets. With an increase in dye concentration, all the signals of the fluorines exhibited progressive shifts to lower magnetic field, indicating that the fluorine atoms in the aggregate are located outside the aromatic ring of an adjacent dye molecule. The direction of the shifts did not vary from dye to dye, but the extent did, depending on the number of sulfonic groups. The results are used to suggest a molecular model of dye aggregation. The visible absorption spectra of the dye solutions showed a single monomer/dimer equilibrium. This result permitted the calculation of aggregation constants, K. These K values agreed quite well with those determined by I9F NMR spectroscopy. The aggregation constants depended on the presence of fluorine atoms and the number of sulfonic groups. The mechanism of these effects on the aggregation is also discussed in detail.
Introduction It is well-known that aggregated molecules behave differently from their monomers. For example, the electronic absorption spectra of dye aggregates in aqueous solutions are quite different from those of dye monomers. Recently the characteristics of aggregates such as J-aggregated dyes have been studied exten~ i v e l y . ' - ~The authors of these studies tried to utilize photoconductivity and intense electroluminescence of J-aggregates as a sensitizer. Cyanine dyes have also recently been investigated in the same c o n n e ~ t i o n . The ~ ~ ~aggregation behavior of azo dyes is also a matter of interest and has been widely investigated.'-I2 Imae et al. studied the micellization of a surface-active azo dye in aqueous methanol solutions in detai1.I3$I4 Shimomura et al. prepared azobenzene-containing amphiphiles and investigated their aggregation behaviors in water by means of electron microscopy, differential scanning calorimetry, and absorption ~pectroscopy.'~ As a result, it was found that the aggregate structures depended on the length of the alkyl chain in the amphiphiles and were classified into H-aggregates and J-aggregates. We have studied the aggregation behavior of azo dyes containing one trifluoromethyl group in aqueous solutions by means of visible absorption spectra and 19F N M R measurements.I6-'* From the chemical shifts of the fluorine atoms, an aggregate model was proposed. Blears et al.,19*20 Veselkov et al.,21,22and Asakura et alez3applied IH N M R spectroscopy to aggregation studies, but the assignment of 'H N M R signals is more complicated and the change in the chemical shifts of IH N M R is smaller than that of I9F NMR. Furthermore, 19FNMR spectroscopy is a powerful technique for the exploration of the microenvironment in the vicinity of fluorine atoms. 'Present address: Faculty of Textile Science and Technology, Shinshu University, Ueda-shi, Nagano 386, Japan. 'Present address: Jissen Women's University, Hino-shi, Tokyo 191, Japan
0022-3654/90/2094-3766$02.50/0
In the present work, monoazo sulfonic dyes containing pentafluoroaniline as a diazo component were prepared, and their ( I ) Dan, P.; Willner, I.; Dixit, N. S.; Mackey, R. A. J. Chem. SOC.,Perkin Trans. 2 1984, 455. (2) Hada, H.; Hanawa R.; Haraguchi, A.; Yonezawa, Y. J. Phys. Chem. 1985. 89, 560. (3) Natoli, L. M.; Ryan, M. A,; Spitler, M. T. J . Phys. Chem. 1985,89, 1448. (4) Era, M.; Hayashi, S.; Tsutsui, T.; Saito, S. J . Chem. SOC.,Chem. Commun. 1985, 557. (5) Herz, A. H . Photogr. Sci. Eng. 1974, 18, 323. (6) Herz. A. H . Adu. Colloid Interface Sci. 1977. 8. 237. (7) Pugh, D.; Giles, C. H.; Duff, D. G.Trans. Faraday Soc. 1971,67, 563. (8) Duff, D. G . ;Kirkwood, D. J.; Stevenson, D. M. J . SOC.Dyers Colour. 1977, 93, 303. (9) Datyner, A.; Floers, A. G.; Pailthorpe, M. T. J . Colloid Interface Sci. 1980, 74, 7 1 , (IO) Jones, F.; Kent, D. R. Dyes Pigm. 1980, 1 , 39. ( 1 1) Reeves, R. L.; Maggio, M. S.; Harkaway, S. A. J. Phys. Chem. 1979, 83. 2359. . . -.. ~ ( I 2) Takagishi, T.; Fujii, S.; Kuroki, N. J . Colloid Interface Sci. 1983, 94, 114.
(13) Imae, T.; Mori, C.; Ikeda, S. J . Chem. SOC.,Faraday Trans. 1 1982, 78, 1359.
(14) Imae, T.; Mori, C.; Ikeda, S. J . Chem. SOC.,Faraday Trans. I 1982, 78, 1369.
( I S ) Shimomura, M.; Ando, R.; Kunitake, T. Eer. Bunsen-Ges. Phys. Chem. 1983, 87, 1134. (16) Hamada, K.; Kubota, H.; Ichimura, A,; Iijima, T.; Amiya, S. Eer. Bunsen-Ges. Phys. Chem. 1985, 89, 859. (17) Hamada, K.; Take, S.; lijima, T.; Amiya, S. J. Chem. Soc., Faraday Trans. I 1986, 82, 3141. ( 1 8 ) Skrabal, P . ; Bangerter, F.; Hamada, K.; Iijima, T. Dyes Pigm. 1987, 8, 371. (19) Blears, D. J.; Danyluk, S. S. J. Am. Chem. SOC.1966, 88, 1084. (20) Blears, D. J.; Danyluk, S. S . J. Am. Chem. SOC.1967, 89, 21. (21) Veselkov, A. N.; Dymant, L. N.; Kulikov, E. L. Khim. Fir. 1984.3, 1108.
(22) Veselkov. A. N.; Dymant, L. N.; Kulikov, E. L. Zh. Sfrucf.Khim. 1985, 26, 43.
0 1990 American Chemical Society
The Journal of Physical Chemistry, Vol. 94,No. 9, 1990 3167
Aggregation of Azo Dyes in Aqueous Solutions F
F
HO.
FA S
F,
\
S03Na
HO.
F
\
SOsNa
FAR
HO,
AS Figure 1. Dyes used.
\
S03Na
,Soda
\
AR
I
300
S03Na
400 500 Wavelengthhm
S03Na
1 600
Figure 2. Absorption spectra of aqueous dye solutions at 298 K: -, FAS (3.43 X IO-' mol dm"); ---, FAR (2.43 X lo-' mol dm-)); ---, AS mol dm-'); ----, AR (2.64 X IO-' mol dm-)). (2.52 X
aggregation behaviors were examined by means of electronic absorption and I9F NMR spectroscopy. The aggregation constants for these dyes were determined and compared with those for the corresponding monoazo sulfonic dyes containing aniline as a diazo component. The effects of fluorine atoms and charged groups in the dyes on the aggregation behavior are discussed. In addition, molecular models of the dye aggregates are proposed.
Experimental Section Four azo dyes, sodium salts of l-pentafluorophenylazo-2hydroxy-6-naphthalenesulfonic acid (FAS), l-pentafluorophenylazo-2-hydroxy-3,6-naphthalenedisulfonicacid (FAR), l-phenylazo-2-hydroxy-6-naphthalenesulfonicacid (AS), and 1-phenylazo-2-hydroxy-3,6-naphthalenedisulfonicacid (AR) were used (Figure 1). FAS and FAR were synthesized by coupling of pentafluoroaniline diazotized in 70% aqueous sulfuric acid solution with Schaeffer's acid (2-naphthol-6-sulfonic acid) and R acid (2-naphthol-3,6-disulfonicacid), respectively. The dyes obtained were purified by repeated recrystallization from methanol (FAS) and CH3COOH/n-BuOH/H20 (1 :4:2) solution (FAR), respectively. The purity was confirmed by elemental analysis and thin layer chromatography. AS (Crocein Orange G) and AR (Ponceau G) were purchased from Tokyo Kasei Co., and purified by repeated recrystallization from aqueous ethanol solution. I9F NMR and absorption spectra were measured at 298 K by using a JEOL GX-500 spectrometer and HITACHI 556 double-wavelength double-beam spectrophotometer, respectively. All the measurements were performed under the same conditions as in our previous paper.I6 Results and Discussion Visible Absorption Measurements. The visible absorption spectra of FAS, FAR, AS, and AR in water are shown in Figure (23) Asakura, T.;Ishida, M. J . Colloid Interface Sei. 1989, 130, 184.
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The Journal of Physical Chemistry, Vol. 94, No. 9, I990
Hamada et al.
:#:A
I I
N II
,
I
-85.6
I
-60
-70
I
-80 -90 -100 b/ppm
-85.8 6/ppm
A
F3
10‘ 0
I 600
I
I
200 400 A E /m‘ mol”
Figure 4. Plots of ( A c / C , ) ~ /against ~ A< at 298 K: 0, FAS (458 nm); 0, FAR (493 nm); A, A S (505 nm); A, AR (508 nm).
JL -75.4
I I
-75.6 bhpm
-80.3
-80.5 ~ I P P ~
Figure 6. I9F N M R spectrum for aqueous FAR solution (2.02X mol dm-’) at 298 K. -85 5
ti
-86 0 SW 11
-
5 -.
a
P
n
ln
10 -
-86.5 0
100
200
A E / m2.mol-’ Figure 5. Plots of (Ac/C,)’/~against At using different values of eD (493 nm) for aqueous FAR solutions at 298 K: 0, C D = 1310; A, CD = 1305; 0,fD =
1300 m2 mol-’. -4 -3 -2 log (Ca/mol.dm-l)
-5
TABLE I: K [dm3 mol-’] Determined by Visible Absorption Measurements FAS FAR AS AR m-FTSO m-FTRb
1180 f 50 70-140 590 f 30 300 f 20 510 f 50 260
* 20
Sodium 1-(3-(trifluoromethyl)phenylaz0)-2-hydroxy-6naphthalenesulfonate (see ref 16). bSodium 1-(3-(trifluoromethyl)phenylazo]-2-hydroxy-3,6-naphthalenedisulfonate(see ref 17). its range is given in the table. The K value for FAS was much larger than for AS, whereas that for FAR was smaller than for AR, indicating that the effects of the fluorine atoms depend on the number of sulfonic groups. Thus the fluorine atoms attached directly to the benzene ring affect the aggregation behavior in a complicated manner. On the other hand, the K values for the corresponding monoazo sulfonic dyes containing a trifluoromethyl group in the benzene ring at 3-position to the azo linkage, i.e., sodium salts of l-(3-(trifluoromethyl)phenylazo)-2-hydroxy-6naphthalenesulfonic acid (m-FTS) and 1-(3-(trifluoromethyl)phenylazo)-2-hydroxy-3,6-naphthalenedisulfonic acid (mFTR),I6,” were little different from those for AS and AR. The aggregation constant for sodium 1-(4-trifluoromethyl)phenylazo)-2-hydroxy-6-naphthalenesulfonate (p-FTS) was determined as 1520 dm3 mol-’ at 300 K,25 indicating that the trifluoromethyl group attached at 4-position to the azo linkage affects the aggregation behavior more greatly than that attached at 3-position. Thus the positions at which functional groups are attached to dye molecules must be considered in discussing their effects on aggregation behavior. In the dyes studied here, all hydrogen atoms (24) Dimicoli, J.-L.; Helene, C. J . Am. Chem. SOC.1973, 95, 1036. (25) Hamada. K.; Fujita, M.; Mitsuishi. M. Manuscript in preparation.
-1
Figure 7. Dependence of the chemical shift, 6, for the F-2 atoms on the dye concentration at 298 K: 0, FAS; 0, FAR. 6o
I
0‘ 0
I
I
1.o
0.5
5
A6/ppm
Figure 8. Plots of ( A I ~ / C , ) I /against ~ A6 for the F-2atoms at 2 FAS; 0, FAR.
:: 0,
in the benzene ring are displaced by fluorine atoms, so that it is possible to discuss the effects of the fluorine atoms without considering the displaced positions. I9F N M R Measurements. An example of I9F N M R spectra is shown in Figure 6 . The shapes of all the NMR spectra observed over the concentration range examined for both FAS and FAR were the same as in the figure. The signal consists of one doublet
J . Phys. Chem. 1990,94, 3769-3775 TABLE 11: K , 6~ 8q, and A8& Determined by I9F NMR Swctroscow F- 1 F-2 F-3 FAS K/dm3 mol-' 1200 f 140 1160 f 30 990 f 150 -87.150 -81.260 b/ppm -76.650 -85.827 -79.215 bD2/ppm -76.428 2.045 0.222 1.323 AgD2/ppm
FAR K/dm3 mol-' bD/ppm
83 f 4
-76.490 -74.781 1.709
bD,/ppm AbD*/pPm
88 f 3 -86.980 -84.725 2.255
88 f 6 -81.520 -79.610 1.910
and two triplets, which correspond to F-1, F-2, and F-3,respectively, as shown in Figure 6. Figure 7 shows the change of the chemical shifts for F-2 with dye concentration. All the other signals of the fluorines such as F-2 showed progressive shifts to lower magnetic field with increasing dye concentration. The aggregation constants, K, were also determined from the change of the chemical shifts given in Figure 7. Assuming a monomer/dimer equilibrium, as mentioned in the previous section, we obtain the following equation24
3769
where A6 = 16 - 6,1, AbD, = ISD, - hD1, and 6 is the observed chemical shift. 6, and, ,6 are the chemical shifts of the monomer and dimer species, respectively. The plots of (A6/Co)i/2against A6 gave straight lines (Figure 8), where extrapolated values to the extreme dilution in Figure 7 were used as .6, K, ,6, 6,, and As,, are given in Table 11. The K values determined from F-1, F-2, and F-3 agreed quite well within experimental errors and were consistent with those obtained from visible absorption measurements. The l9F NMR data gave us another prominent piece of information concerning the location of fluorine atoms. The change of the chemical shifts toward lower magnetic field with increasing dye concentration indicates that the fluorine atoms of the dyes are located outside the aromatic ring of an adjacent dye molecule in the aggregate. The relative spacial location between a fluorine atom and an aromatic ring probably determine the A64 value. Therefore, if we estimate the shape of the ring current in the dyes, we could elucidate the detailed structure of the dye aggregates. Registry No. FAS, 126217-29-6;FAR, 59245-81-7; AS, 1934-20-9; AR, 5859-00-7; 2-naphthol-6-sulfonicacid, 93-01-6; 2-naphthol-3,6-disulfonic acid, 148-75-4.
Formation of Head-to-Tail and Side-by-Side Aggregates of Photochromic Spiropyrans in Bilayer Membrane Takahiro Seki* and Kunihiro Ichimura Research Institute for Polymers and Textiles, 1 - 1 -4 Higashi, Tsukuba, Ibaraki 305, Japan (Received: October 2, 1989)
Aggregation phenomenon and thermal isomerization behaviors of photochromic spiropyran (SP) compounds in dioctadecyldimethylammonium (2Ci8N+2CI)bilayer membrane are reported. Spiropyran compounds having two alkyl chains form J-aggregate (head-to-tail) or H-aggregate (side-by-side) in the bilayer when they are converted to the photoinduced merccyanine form by UV light (PMC). The type of the aggregate depends on the chemical structure of this photochromic molecule. One type of PMC forms J-aggregate (J-PMC) at the mixing molar ratio of the spiropyran to 2C,,NC2C1 ( R ) of more than 0.01, and the other type forms H-aggregate (H-PMC) at R > 0.02. It is suggested in comparison with other isotropic media that an orientation effect of the anisotropic environment formed by the bilayer is essential for the controlled aggregate formation. J-PMC is stable in the bilayer regardless of the crystal F= liquid crystal phase change, and H-PMC, on the other hand, is formed only in the crystal (gel) phase. Aggregation retards the rate of the thermal isomerization (PMC SP) to large extents, depending on the aggregation type. This paper reports, for the first time, the aggregation phenomenon of photochromic spiropyran compounds in the bilayer matrix.
-
Introduction Aggregation behaviors of chromophores such as chlorophylls,' cyanines,2 merocyanines,2b and azobenzenes3 have been investigated in the systems of both naturally occurring and synthetic bilayer membranes. Bilayer membranes are composed of twodimensional amphiphile arrays and such matrices provide characteristic chromophore organization. From a viewpoint of biological interest, these systems may be useful for understanding membrane phenomena related to biological pigments. Aggregation (Hmanner, whether "head-to-tail" ( J - t y ~ e )or ~ ."side-by-side" ~ type),s depends on the combination of chromophores and chemical structure of bilayers in~estigated.'-~Dye aggregation in bilayers is frequently sensitive to the thermally induced fluidity change of membrane matrices termed as the crystal (gel) * liquid crystal phase transition (the temperature, T,) Kurihara et have demonstrated that side-by-side type dimer formation of a longchain cyanine dye in egg yolk phosphatidylcholine bilayer brings about reversible thermal changes in the absorption spectrum. Kunitake and co-workers have reported reversible J- and H-ag-
* To whom correspondence should be addressed. 0022-36S4/90/2094-3769$02.50/0
gregation (below T,) and dissociation (above T,) of ionic cyanine dyes absorbed onto a variety of synthetic bilayer membranes.2 This reversible process leads to drastic spectral changes between an aggregate band and a monomer band. Shimomura et aL3 synthesized a large number of bilayer-forming ammonium amphiphiles containing an azobenzene unit and demonstrated that the aggregation type of this chromophore is controlled by the methylene spacer length connecting the chromophore and the ammonium head group. As in the case of the above examples, aggregation of azobenzene units occurs in the temperature region below T,. (1) (a) Csorba, J.; Szabad, J.; Eldei, L.; Fafszi, C. Photochem. Photobiol. 1975, 21, 377. (b) Lee, A. G . Biochemistry 1975, 14, 4397. (2) (a) Kurihara, K.; Toyoshima, Y.; Sukigara, M. J . Phys. Chem. 1977, 81, 1833. (b) Nakashima, N.; Ando, R.; Fukushima, H.; Kunitake, T. J . Chem. SOC.,Chem. Commun. 1982, 707. (c) Nakashima, N.; Kunitake, T. Chem. Lett. 1983, 1577. (d) Ishikawa, Y.;Kunitake, T. J . Synth. Om. Chem., Jpn. 1989, 47, 535.
(3) Shimomura. M.; Ando. R.;Kunitake, T. Ber. Bunsen-Ges. Phys. Chem. 1983, 87, 1134 and references therein. (4) (a) Jelley, E. E. Nature 1936, 138, 1009. (b) Scheibe, G.Angew. Chem. 1936, 49, 563. (5) H e n , A. H. Photogr. Sci. Eng. 1974, 18, 323.
0 1990 American Chemical Society
