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.…
Author details: | Manuel Martin UtechtORCiDGND, Tillmann KlamrothORCiDGND, Peter SaalfrankORCiDGND |
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DOI: | https://doi.org/10.1039/c1cp22793a |
ISSN: | 1463-9076 |
Title of parent work (English): | Physical chemistry, chemical physics : a journal of European Chemical Societies |
Publisher: | Royal Society of Chemistry |
Place of publishing: | Cambridge |
Publication type: | Article |
Language: | English |
Year of first publication: | 2011 |
Publication year: | 2011 |
Release date: | 2017/03/26 |
Volume: | 13 |
Issue: | 48 |
Number of pages: | 7 |
First page: | 21608 |
Last Page: | 21614 |
Funding institution: | Deutsche Forschungsgemeinschaft [Sonderforschungsbereich 658] |
Organizational units: | Mathematisch-Naturwissenschaftliche Fakultät / Institut für Chemie |
Peer review: | Referiert |