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Issue 48, 2011
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Optical absorption and excitonic coupling in azobenzenes forming self-assembled monolayers: a study based on density functional theory

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Abstract

Based on the analysis of optical absorption spectra, it has recently been speculated that the excitonic coupling between individual azobenzene-functionalized alkanethiols arranged in a self-assembled monolayer (SAM) on a gold surface could be strong enough to hinder collective trans–cisisomerization—on top of steric hindrance [Gahl et al., J. Am. Chem. Soc., 2010, 132, 1831]. Using models of SAMs of increasing complexity (dimer, linear N-mers, and two-dimensionally arranged N-mers) and density functional theory on the (TD-) B3LYP/6-31G* level, we determine optical absorption spectra, the nature and magnitude of excitonic couplings, and the corresponding spectral shifts. It is found that at inter-monomer distances of about 20 Å and above, TD-B3LYP excitation frequencies (and signal intensities) can be well described by the frequently used point-dipole approximation. Further, calculated blue shifts in optical absorption spectra account for the experimental observations made for azobenzene/gold SAMs, and hint to the fact that they can indeed be responsible for reduced switching probability in densely packed self-assembled structures.

Graphical abstract: Optical absorption and excitonic coupling in azobenzenes forming self-assembled monolayers: a study based on density functional theory

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Publication details

The article was received on 02 Sep 2011, accepted on 19 Oct 2011 and first published on 09 Nov 2011


Article type: Paper
DOI: 10.1039/C1CP22793A
Citation: Phys. Chem. Chem. Phys., 2011,13, 21608-21614
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    Optical absorption and excitonic coupling in azobenzenes forming self-assembled monolayers: a study based on density functional theory

    M. Utecht, T. Klamroth and P. Saalfrank, Phys. Chem. Chem. Phys., 2011, 13, 21608
    DOI: 10.1039/C1CP22793A

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