Determining the Orientation and Molecular Packing of Organic Dyes on a TiO2 Surface Using X-ray Reflectometry

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• 作者：Matthew J. Griffith ; Michael James ; Gerry Triani ; Pawel Wagner ; Gordon G. Wallace ; David L. Officer
• 刊名：Langmuir
• 出版年：2011
• 出版时间：November 1, 2011
• 年：2011
• 卷：27
• 期：21
• 页码：12944-12950
• 全文大小：881K
• 年卷期：v.27,no.21(November 1, 2011)
• ISSN：1520-5827

文摘

The determination of the orientation and molecular density for several porphyrin dyes adsorbed on planar TiO₂ surfaces using X-ray reflectometry (XRR) is reported. Adsorption of nanoscale water layers occurred rapidly upon exposure of freshly prepared TiO₂ surfaces to ambient conditions; however, this was successfully eliminated, resulting in clearly discernible adsorbed dye layers for sensitized surfaces. Adsorbed dye orientations, determined from computations constrained by the measured dye layer thickness, were calculated to have a binding tilt angle of 35掳鈥?0掳. Combining the XXR data with the orientation models indicates that the porphyrins form densely packed surfaces with an intermolecular spacing of 3鈥? 脜, consistent with 蟺鈥撓€ stacking interactions. Changes in the molecular size of probe dyes were reflected in corresponding changes in the measured dye layer thickness, confirming the ability of this technique to resolve small variations in dye layer thickness and consequently adsorption orientation. Application of these results to understanding the behavior of dye-sensitized devices is discussed.