TY  - JOUR
A1  - Utecht, Manuel Martin
A1  - Klamroth, Tillmann
A1  - Saalfrank, Peter
T1  - Optical absorption and excitonic coupling in azobenzenes forming self-assembled monolayers a study based on density functional theory
JF  - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2  - 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 that they can indeed be responsible for reduced switching probability in densely packed self-assembled structures.
Y1  - 2011
U6  - https://doi.org/10.1039/c1cp22793a
SN  - 1463-9076
VL  - 13
IS  - 48
SP  - 21608
EP  - 21614
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Luo, Ying
A1  - Utecht, Manuel Martin
A1  - Dokic, Jadranka
A1  - Korchak, Sergey
A1  - Vieth, Hans-Martin
A1  - Haag, Rainer
A1  - Saalfrank, Peter
T1  - Cis-trans isomerisation of substituted aromatic imines a comparative experimental and theoretical study
JF  - ChemPhysChem : a European journal of chemical physics and physical chemistry
N2  - The cis-trans isomerisation of N-benzylideneaniline (NBA) and derivatives containing a central C=N bond has been investigated experimentally and theoretically. Eight different NBA molecules in three different solvents were irradiated to enforce a photochemical trans (hv) -> cis isomerisation and the kinetics of the thermal backreaction cis (Delta)-> trans were determined by NMR spectroscopy measurements in the temperature range between 193 and 288 K. Theoretical calculations using density functional theory and Eyring transition-state theory were carried out for 12 different NBA species in the gas phase and three different solvents to compute thermal isomerisation rates of the thermal back reaction. While the computed absolute rates are too large, they reveal and explain experimental trends. Time-dependent density functional theory provides optical spectra for vertical transitions and excitation energy differences between trans and cis forms. Together with isomerisation rates, the latter can be used to identify "optimal switches" with good photochromicity and reasonable thermal stability.
KW  - density functional calculations
KW  - imines
KW  - isomerization
KW  - photochemistry
KW  - thermochemistry
Y1  - 2011
U6  - https://doi.org/10.1002/cphc.201100179
SN  - 1439-4235
VL  - 12
IS  - 12
SP  - 2311
EP  - 2321
PB  - Wiley-VCH
CY  - Weinheim
ER  -