J. Phys. Chem. 1992,96,4279-4281
4279
Primary Process of Illumination Effect on the Ru(bpy)t+-Cataiyzed Beiousov-2 habotinskii Reaction M. Jinguji,* M. Ishihara, and T. Nakazawa Department of Chemistry, Medical University of Yamanashi, Tamaho, Nakakoma. Yamanashi 409-38, Japan (Received: November 18, 1991)
The primary process for the influence of light on the Ru(bpy),"-catalyzed Belousov-Zhabotinskii reaction system was investigated. The wavelength dependence of the illumination effect on oscillations was found to be in good correlation with the absorption spectrum of Ru(bpy)?+. The dynamic behavior of bromide ion was measured simultaneously with that of Ru(bpy)?+ during illumination on the oscillatory reaction and the acidic bromate-Ru(bpy)?+ systems. The results suggest that the inhibitory effect of illumination results from the formation of bromide ion in the reaction of the excited state of Ru(bpy),2t with bromate.
Introduction Much interest has recently been shown in the study of the light-sensitive oscillatory reaction systems, e.g., the BelousovZhabotinskii (BZ) reaction,'" the Bray-Liebhafsky reaction,' the Briggs-Rauscher reaction,*v9the pH oscillator,'OJl and the uncatalyzed chemical oscillators.I2 The BZ reaction containing R ~ ( b p y ) , ~as + catalyst is particularly interesting among the light-sensitive systems because of its peculiar photochemical and photophysical pr~perties.'~Gaspar et ale3reported that the period and amplitude of the oscillations are affected by the visible light and even inhibition of oscillations was observed. Kuhnert4Jstudied the illumination effects on wave propagation in the distributed oscillating system in the context of image processing and storage. More recently, Jinguji et ala6reported on the photoinduced formation of new patterns of traveling waves moving as straight lies. In these studies the visible light was assumed to affect the release of bromide ion by the photochemical reaction of the ruthenium complexes. In the present paper we investigated the primary process for the influence of light on the Ru(bpy),*+-catalyzed system. We measured the wavelength and intensity dependence of the illumination effect on temporal oscillations. Simultaneous measurements of Ru(bpy):+ and bromide ion were carried out during illumination on the oscillatory reaction and the acidic bromateRu(bpy):+ systems. It was found that the oxidation of Ru(bpy):+ to Ru(bpy)l+ was induced by illumination and at the same time bromide ion was formed.
Experimental Section Most of the experiments were performed in a spectrophotometric cell at room temperature. All chemicals were of analytical grade and used without further purification, and all solutions were prepared from distilled, deionized water. The initial composition (1) Vavilin, V. A.; Zhabotinskii, A. M.; Zaikin, A. N. Russ. J . Phys. Chem. 1968,42, 1649. (2) Busse, H.;Has, B. Nature 1973, 244, 203. (3) Gaspar, V.; Bazsa, G.; Beck, M. T. Z . Phys. Chem. (Leipziq) 1983, 264, 43. (4) Kuhnert, L. Nature 1986,319, 393; Natunuissenschafren 1986,73,96. (5) Kuhnert, L.; Agladze, K. I.; Krinsky, V. I. Nature 1989, 337, 244. (6) Jinguji, M.; Ishihara, M.; Nakazawa, T. J . Phys. Chem. 1990, 94, 1226. (7) Sharma, K. R.; Noyes, R. M. J . Am. Chem. SOC.1975, 97, 202. (8) Dulos, E.; De Kepper, P. Biophys. Chem. 1983, 18, 211. (9) Kumpinsky, E.; Eptein, I. R.; De Kepper, P. Inr. J. Chem. Kiner. 1985, 17, 345. (10) Rabai, G.; Kustin, K.; Epstein, I. R. J . Am. Chem. SOC.1989, ZZZ,
8271. (11) Mori, Y.; Srivastava, P. K.; Hanazaki, I. Chem. Lerr. 1991, 669. (12) Srivastava, P. K.; Mori, Y.; Hanazaki, I. Chem. Phys. Lett. 1991,177, 213. (13) Kalyanasundaram, K. Coord. Chem. Reu. 1982, 46, 159.
of the system was the following: [KBr0310= 0.06 M, [CH2(C00H)2]o = 0.25 M, [Ru(bpy),2+l0= 1 X lo4 M, and [H2SO4Io = 1 M. The solution was stirred magnetically at a constant rate throughout the experiment. The batch reaction was followed by measuring the light absorption of R ~ ( b p y ) , ~using + a spectrophotometer (JASCO WIDEC-500). In the measurements during illumination a suitable interference filter was attached to the window of its detector to remove the scattering of the illumination light. The reaction was also followed by measuring the potential from a bromide ion specific electrode (Horiba 8005-06T) simultaneously with the absorption measurement of Ru(bpy),2+. In this case, a cylindrical cell was used to allow the insertion of the electrodes. Ru(bpy)?+ was monitored by the transmittance at 488 nm from argon ion laser (NEC GLG-3050A). Illumination was carried out with a high-pressure mercury lamp (Ushio USH-500D) through a monochromator (Ritsu MC-25NP) or a band-pass filter. The light intensity was varied with a series of neutral-density filters (1-70%) and measured by a power meter (Ushio UIT-101) at the window of the cell.
Results and Discussion The oscillatory reaction occurs without the induction period when the BZ solutions are mixed in a spectrophotometric cell. Once oscillations begin, both the amplitude and period reach steady values about 10 min after and change very little during much of the reaction time in the dark. Oscillations were clearly observed in the absorptions corresponding to Ru(bpy):+ and Ru(bpy),'+, respectively, which were o p p i t e in phase due to the redox reaction in the oscillatory system. When the oscillating solution was illuminated with visible light, both the amplitude and period of the oscillations were changed and even inhibition of oscillations was observed. First we measured the light wavelength and intensity dependence of these illumination effects. Here we defined conveniently the efficiency of the illumination effect as the percentage of the change in the amplitude or the period of oscillations: AA (%) = (Ao- A ) / A o X 100 or AT (%) = (To- T)/To X 100, where A. and A or To and T a r e the amplitudes or the periods just before and after illumination, respectively. The oscillatory reaction was followed by measuring the absorbance of Ru(bpy):+ at 450 or 500 nm according to the wavelength of the illumination light. Figure 1 demonstrates the wavelength dependence of the efficiency, AA and AT. Light reduced the amplitude and shortened the period of the oscillatory reaction being studied. The wavelength dependence was found to be in good correlation with the absorption spectrum of Ru(bpy)?+ though the scattering of points was considerable. It should be pointed out here that there was little effect even when the solution was illuminated with the light (>600nm) using a cutoff filter instead of the monochromator, which corresponds to the first weak absorption band of Ru(bpy)?+.
0022-3654I92 12096-4279503.OO ,I O1 0 1992 American Chemical Society I
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4280 The Journal of Physical Chemistry, Vol. 96, No. 11, 1992
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