Dynamical Orientation of Large Molecules on Oxide Surfaces and its Implications for Dye-Sensitized Solar Cells

Thomas P. Brennan, Jukka T. Tanskanen, Jonathan R. Bakke, William H. Nguyen, Dennis Nordlund, Michael F. Toney, Michael D. McGehee, Alan Sellinger, Stacey F. Bent

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15 Scopus citations


A dual experimental-computational approach utilizing near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and density functional theory-molecular dynamics (DFT-MD) is presented for determining the orientation of a large adsorbate on an oxide substrate. A system of interest in the field of dye-sensitized solar cells is studied: an organic cyanoacrylic acid-based donor-π-acceptor dye (WN1) bound to anatase TiO2. Assessment of nitrogen K-edge NEXAFS spectra is supported by calculations of the electronic structure that indicate energetically discrete transitions associated with the two π systems of the C-N triple bond in the cyanoacrylic acid portion of the dye. Angle-resolved NEXAFS spectra are fitted to determine the orientation of these two orbital systems, and the results indicate an upright orientation of the adsorbed dye, 63 from the TiO2 surface plane. These experimental results are then compared to computational studies of the WN1 dye on an anatase (101) TiO2 slab. The ground state structure obtained from standard DFT optimization is less upright (45 from the surface) than the NEXAFS results. However, DFT-MD simulations, which provide a more realistic depiction of the dye at room temperature, exhibit excellent agreement - within 2 on average - with the angles determined via NEXAFS, demonstrating the importance of accounting for the dynamic nature of adsorbate-substrate interactions and DFT-MD's powerful predictive abilities. © 2013 American Chemical Society.
Original languageEnglish (US)
Pages (from-to)4354-4363
Number of pages10
JournalChemistry of Materials
Issue number21
StatePublished - Nov 4 2013
Externally publishedYes

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): KUS-C1-015-21
Acknowledgements: This publication was based on work supported by the Center for Advanced Molecular Photovoltaics (CAMP) (Award No. KUS-C1-015-21), made by King Abdullah University of Science and Technology (KAUST). Portions of this research were carried out at the Stanford Synchrotron Radiation Lightsource, a Directorate of SLAC National Accelerator Laboratory and an Office of Science User Facility operated for the U.S. Department of Energy Office of Science by Stanford University under SSRL proposal #3338. T.P.B. would like to thank the Albion Walter Hewlett Fellowship for financial support. J.T.T. gratefully acknowledges the Academy of Finland (Grant 256800/2012) and the Finnish Cultural Foundation for financial support. J.R.B acknowledges funding from the National Science Foundation (NSF) Graduate Fellowship. We would like to thank Dr. Han Bo-Ram Lee for assistance with the ALD of TiO2.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.


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