Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 11, Issue 2, Pages 767-775Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.200400323
Keywords
electrochemistry; electrochromic material; hybrid film; ruthenium; tungsten trioxide
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A tungsten trioxide (WO3)/tris(2,2'-bipyridine)ruthenium(II) ([Ru(bPY)(3)](2+); bpy = 2,2'-bipyridine)/poly(sodium 4-styrenesulfonate) (PSS) hybrid film was prepared by electrodeposition from a colloidal triad solution containing peroxcitungstic acid (PTA), [Ru(bPY)(3)](2+), and PSS. A binary solution of [Ru(bpy)(3)](2+) and PTA (30 vol % ethanol in water) gradually gave an orange precipitate, possibly caused by the electrostatic interaction between the cationic [Ru(bPY)(3)](2+) and the anionic PTA. The addition of PSS to the binary PTA/[Ru(bpy)(3)](2+) solution remarkably suppressed this precipitation and caused a stable, colloidal triad solution to form. The spectrophotometric measurements and lifetime analyses of the photoluminescence from the excited [Ru(bPY)(3)](2+) ion in the colloidal triad solution suggested that the [Ru(bpy)(3)](2+) ion is partially shielded from electrostatic interaction with anionic PTA by the anionic PSS polymer chain. The formation of the colloidal triad made the ternary [Ru(bpy)(3)](2+)/PTA/PSS solution much more redox active. Consequently, the rate of electrodeposition of WO3 from PTA increased appreciably by the formation of the colloidal triad, and fast electrodeposition is required for the unique preparation of this hybrid film. The absorption spectrum of the [Ru(bpy)(3)](2+) ion in the film was close to its spectrum in water, but the photoexcited state of the [Ru(bPY)(3)](2+) ion was found to be quenched completely by the presence of WO3 in the hybrid film. The cyclic voltammogram (CV) of the hybrid film suggested that the [Ru(bpy)(3)](2+) ion performs as it is adsorbed onto WO3 during the electrochemical oxidation. An ohmic contact between the [Ru(bpy)(3)](2+) ion and the WO3 surface could allow the electrochemical reaction of adsorbed [Ru(bPY)(3)](2+). The composition of the hybrid film, analyzed by electron probe microanalysis (EPMA), suggested that the positive charge of the [Ru(bpy)(3)](2+) ion could be neutralized by partially reduced WO3 ions, in addition to Cl- and PSS units, based on the charge balance in the film. The electrostatic interaction between the WO3- ion and the [Ru(bpy)(3)](2+) ion might be responsible for forming the electron transfer channel that causes the complete quenching of the photoexcited [Ru(bpy)(3)](2+) ion, as well as the formation of the ohmic contact between the [Ru(bpy)(3)](2+) ion and WO3. A multicolor electrochromic performance of the WO3/[Ru(bpy)(3)](2+)/PSS hybrid film was observed, in which transmittances at 459 and 800 nm could be changed, either individually or at once, by the selection of a potential switch. Fast responses, of within a few seconds, to these potential switches were exhibited by the electrochromic hybrid film.
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