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

  • 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-cis isomerization-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 angstrom 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 thatBased 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-cis isomerization-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 angstrom 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.show moreshow less

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Metadaten
Author:Manuel Utecht, Tillmann Klamroth, Peter SaalfrankORCiDGND
DOI:https://doi.org/10.1039/c1cp22793a
ISSN:1463-9076 (print)
Parent Title (English):Physical chemistry, chemical physics : a journal of European Chemical Societies
Publisher:Royal Society of Chemistry
Place of publication:Cambridge
Document Type:Article
Language:English
Year of first Publication:2011
Year of Completion:2011
Release Date:2017/03/26
Volume:13
Issue:48
Pagenumber:7
First Page:21608
Last Page:21614
Funder:Deutsche Forschungsgemeinschaft [Sonderforschungsbereich 658]
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Chemie
Peer Review:Referiert