Single Component Self-Assembled Monolayers of Aromatic Azo-Biphenyl: Influence of the Packing Tightness on the SAM Structure and Light-Induced Molecular Movements

Authors

  • Mark Elbing,

    1. Forschungszentrum Karlsruhe GmbH Institute for Nanotechnology P.O. Box 3640, D-76021 Karlsruhe (Germany)
    2. Department of Chemistry and Biochemistry Center for Polymers and Organic Solids University of California, Santa Barbara, CA 93106-5090 (USA)
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  • Alfred Błaszczyk,

    1. Forschungszentrum Karlsruhe GmbH Institute for Nanotechnology P.O. Box 3640, D-76021 Karlsruhe (Germany)
    2. Faculty of Commodity Science Al. Niepodleglości 10, 60-967 Poznań (Poland)
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  • Carsten von Hänisch,

    1. Forschungszentrum Karlsruhe GmbH Institute for Nanotechnology P.O. Box 3640, D-76021 Karlsruhe (Germany)
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  • Marcel Mayor,

    Corresponding author
    1. Forschungszentrum Karlsruhe GmbH Institute for Nanotechnology P.O. Box 3640, D-76021 Karlsruhe (Germany)
    2. Department of Chemistry, University of Basel St. Johannsring 19, CH-4056 Basel (Switzerland)
    • Forschungszentrum Karlsruhe GmbH Institute for Nanotechnology P.O. Box 3640, D-76021 Karlsruhe (Germany).
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  • Violetta Ferri,

    1. Dipartimento di Chimica Università di Ferrara, I-44100 Ferrara (Italy)
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  • Christian Grave,

    1. Dipartimento di Chimica Università di Ferrara, I-44100 Ferrara (Italy)
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  • Maria Anita Rampi,

    Corresponding author
    1. Dipartimento di Chimica Università di Ferrara, I-44100 Ferrara (Italy)
    • Dipartimento di Chimica Università di Ferrara, I-44100 Ferrara (Italy).
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  • Giuseppina Pace,

    1. Institut de Science et d'Ingénierie Supramoléculaires/CNRS UMR 7006, Université Louis Pasteur 8 allée Gaspard Monge, F-67000 Strasbourg (France)
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  • Paolo Samorì,

    Corresponding author
    1. Institut de Science et d'Ingénierie Supramoléculaires/CNRS UMR 7006, Université Louis Pasteur 8 allée Gaspard Monge, F-67000 Strasbourg (France)
    2. Istituto per la Sintesi Organica e la Fotoreattività Consiglio Nazionale delle Ricerche Via Gobetti 101, I-40129 Bologna (Italy)
    • Institut de Science et d'Ingénierie Supramoléculaires/CNRS UMR 7006, Université Louis Pasteur 8 allée Gaspard Monge, F-67000 Strasbourg (France).
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  • Andrei Shaporenko,

    1. Angewandte Physikalische Chemie, Universität Heidelberg Im Neuenheimer Feld 253, D-69120 Heidelberg (Germany)
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  • Michael Zharnikov

    Corresponding author
    1. Angewandte Physikalische Chemie, Universität Heidelberg Im Neuenheimer Feld 253, D-69120 Heidelberg (Germany)
    • Angewandte Physikalische Chemie, Universität Heidelberg Im Neuenheimer Feld 253, D-69120 Heidelberg (Germany).
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  • This work was supported by the EU through the Marie Curie EST—SUPER (MEST-CT-2004-008128), LIMM (IST-2001-35503), the RTNs PRAIRIES (MRTN-CT-2006-035810), the ERA-Chemistry project SurConFold, the ESF-SONS2-SUPRAMATES project, the Regione Emilia-Romagna PRIITT Nanofaber Net-Lab, the DFG grant (ZH 63/9-2), the Swiss National Science Foundation (SNF), and the NCCR Nanoscience of the SNF. MZ thank M. Grunze for the support, C. Wöll for the technical cooperation at BESSY II, and BESSY II staff for the assistance during the experiments at the synchrotron. The experiments at MAX-lab were supported by the EU through the IA-SFS project within the Sixth Framework Programme. Supporting Information is available online from Wiley InterScience or from the author

Abstract

Aiming at modulating the packing density within functional self-assembled monolayers (SAMs), two azo-biphenyl derivatives AZO1 and AZO2 comprising a terminal sulfur anchor group have been designed and synthesized. While AZO1 allows for a coplanar arrangement of both biphenyl subunits, additional steric repulsion due to two methyl side groups attached to the footing biphenyl of AZO2 results in an increased intermolecular distance within the SAM, providing additional free volume. SAMs of both derivatives on gold and platinum substrates have been formed and thoroughly investigated by photoelectron (XPS) and near-edge absorption fine structure (NEXAFS) spectroscopy as well as cyclic voltammetry and scanning tunneling microscopy. These measurements confirmed the formation of tightly packed SAMs for AZO1, while AZO2 formed SAMs consisting of less organized and more loosely packed molecules. Optical investigations of both azo derivatives in solution as well as their SAMs displayed efficient photoisomerization in solution and in SAMs. Comparable maximal cis/trans ratios of ca. 0.9 have been observed in all cases upon irradiation at λ = 370 and 360 nm for AZO1 and AZO2, respectively. The thermally induced cis → trans back reaction on AZO1 was found to be slower by a factor of 3 in SAMs as compared to solution, while AZO2 displayed comparable rates of the back reaction in both environments. This behavior can be explained by the different nature of molecular isomerization in the two SAM systems: whereas the isomerization in AZO1 SAMs takes place in a highly coordinated, collective way and involves many adjacent molecules, AZO2 species behave rather individually even packed in SAMs, such that their isomerization process is similar in SAMs and in solutions.

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