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Controllable Adsorption and Ideal H-Aggregation Behaviors of Phenothiazine Dyes on the Tungsten Oxide Nanocolloid Surface Kenta Adachi,*,† Tomohiro Mita,† Taiki Yamate,† Suzuko Yamazaki,† Hideaki Takechi,‡ and Hitoshi Watarai‡ †
Department of Environmental Science & Engineering, Graduate School of Science & Engineering, Yamaguchi University, Yamaguchi 753-8512, Japan, and ‡Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan Received June 17, 2009. Revised Manuscript Received July 17, 2009
The monomer-aggregate equilibrium of four phenothiazine (PN) dyes, containing thionine (TH), methylene blue (MB), new methylene blue (NMB), and 1,9-dimethylmethylene blue (DMB), in the tungsten(VI) oxide (WO3) nanocolloid solution has been investigated by means of UV-vis spectroscopy. Addition of PN dye into the WO3 nanocolloid solution brought about significant changes in the absorption spectrum, suggesting the formation of H-type (face-to-face fashion) trimer on the WO3 nanocolloid surface. The adsorptivity of PN dyes onto the WO3 nanocolloid surface was diminished by the raising the ionic strength, indicating the evidence of the electrostatic interaction between cationic PN dye and negatively charged WO3 nanocolloids. The detail analysis of each spectral data provided insight into the effect of molecular structure of PN dyes on the adsorption and aggregation behaviors on the WO3 nanocolloid surface. Moreover, in situ measurement of PN dye aggregation using the centrifugal liquid membrane (CLM) technique revealed that the aggregation of PN dyes on the WO3 nanocolloid surface proceeded in a two-step three-stage (monomer f dimer f trimer) formation. The aggregation mechanism of PN dyes on the WO3 nanocolloid surface was discussed on the basis of Kasha’s exciton theory.
1. Introduction The self-assemblies of molecules are ubiquitous in nature where they help, perform, and control all the important functions and processes of life.1,2 For instance, chlorophylls are organized as nanometer-sized rod-shaped aggregates and act as an initiator of photosynthesis in green plants.3-5 The aggregation of dye molecules is known to affect spectroscopic behaviors due to the coherent coupling of molecular excitons6 and eventually leads to the distinct optical properties that the corresponding monomeric dyes do not show.7,8 The structure and spectroscopy of the dye aggregates are of much interest because of the special properties and possible technological applications of the mesoscopic materials which are intermediate between molecules and solids.9,10 One of the important tasks in this field is how to prepare a stable dye aggregate of predetermined size and to regulate its aggregated structure. In recent years, significant interest has been shown in the study of the photophysical and photochemical behavior of dye aggregates on the inorganic semiconductor surfaces in order to create *To whom correspondence should be addressed: e-mail k-adachi@ yamaguchi-u.ac.jp; Fax þ81-83-933-5731. (1) Watson, J. D.; Crick, F. H. C. Nature 1953, 171, 737–738. (2) Tsai, C. D.; Ma, B.; Kumar, S.; Wolfson, H.; Nussinov, R. Crit. Rev. Biochem. Mol. Biol. 2001, 36, 399–433. (3) McDermott, G.; Prince, S. M.; Freer, A. A.; Hawthornthwaite-Lawless, A. M.; Papiz, M. Z.; Cogdell, R. J.; Isaacs, N. W. Nature 1995, 374, 517–521. (4) Olson, J. M. Photochem. Photobiol. 1998, 67, 61–75. (5) Zhang, J.-P.; Fujii, R.; Qian, P.; Inaba, T.; Mizoguchi, T.; Koyama, Y.; Onaka, K.; Watanabe, Y.; Nagae, H. J. Phys. Chem. B 2000, 104, 3683–3691. (6) McRae, E. G.; Kasha, M. J. Chem. Phys. 1958, 28, 721–722. (7) Daehne, L.; Kamiya, K.; Tanaka, J. Bull. Chem. Soc. Jpn. 1992, 65, 2328– 2332. (8) Place, I.; Perlstein, J.; Penner, T. L.; Whitten, D. G. Langmuir 2000, 16, 9042–9048. (9) Kobayashi, T., Ed. J-aggregates; World Scientific Publishing: Singapore, 1996. (10) Wang, M.; Silvia, G. L.; Armitage, B. A. J. Am. Chem. Soc. 2000, 122, 9977–9986.
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new strategies for optical and electronic devices.11-14 Such organic/inorganic hybrid composite materials have numerous possible applications in developing efficient light energy conversion systems, optical devices, and sensors.15,16 Additionally, the composites of dye aggregates and inorganic semiconductors play an important role in biological sensing and imaging applications (e.g., coherent anti-Stokes Raman scattering (CARS) microscopy).17,18 The adsorption and aggregation behaviors of dye molecules on the inorganic semiconductor surfaces should be characterized in detail because fundamental understanding of such behaviors becomes invaluable guidance for practical applications. There have been several literature reports on the dye-metal oxide nanoparticle interactions,19-21 but only limited quantitative information is available on the adsorption and aggregation mechanism. To investigate the adsorption and aggregation behaviors in a dye-inorganic semiconductors hybrid material, we have chosen the phenothiazine (PN) dye and the colloidal tungsten(VI) oxide (WO3) solution systems in this study. PN dyes containing methylene blue (MB) and thionine (TH) are an important group (11) Zhang, Q.; Atay, T.; Tischler, J. R.; Bradley, M. S.; Bulovic, V.; Nurmikko, A. V. Nat. Nanotechnol. 2007, 2, 555–559. (12) Murai, M.; Furube, A.; Yanagida, M.; Hara, K.; Katoh, R. Chem. Phys. Lett. 2006, 423, 417–421. (13) Galoppini, E. Coord. Chem. Rev. 2004, 248, 1283–1297. (14) Linke-Schaetzel, M.; Bhise, A. D.; Gliemann, H.; Koch, T.; Schimmel, T.; Balaban, T. S. Thin Solid Films 2004, 451-452, 16–21. (15) Daniel, M.-C.; Astruc, D. Chem. Rev. 2004, 104, 293–346. (16) Khazraji, A. C.; Hotchandani, S.; Das, S.; Kamat, P. V. J. Phys. Chem. B 1999, 103, 4693–4700. (17) van Manen, H.-J.; Otto, C. Nano Lett. 2007, 7, 1631–1636. (18) M€uller, M.; Zumbusch, A. Chem. Phys. Chem. 2007, 8, 2156–2170. (19) Thomas, K. G.; Kamat, P. V. Acc. Chem. Res. 2003, 36, 888–898. (20) Chandrasekharan, N.; Kamat, P. V.; Hu, J.; Jones, G. J. Phys. Chem. B 2000, 104, 11103–11109. (21) Eckenrode, H. M.; Jen, S.-H.; Han, J.; Yeh, A.-G.; Dai, H.-L. J. Phys. Chem. B 2005, 109, 4646–4653.
Published on Web 08/20/2009
DOI: 10.1021/la902174s
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of organic compounds which have a variety of industrial and scientific applications, for example, as sensitizers in solar energy conversion, redox mediators in catalytic oxidation reactions, active species in electrochromism and dye lasers, ingredients in pharmaceutical preparation, and candidates for cancer photodynamic therapy by intercalating between DNA base layers.22-25 On the other hand, WO3 is one of the important inorganic semiconductor materials, characterized by high chemical and thermal stability and proper energy bandgaps (
