TY  - JOUR
A1  - Bleger, David
A1  - Dokic, Jadranka
A1  - Peters, Maike V.
A1  - Grubert, Lutz
A1  - Saalfrank, Peter
A1  - Hecht, Stefan
T1  - Electronic decoupling approach to quantitative photoswitching in linear multiazobenzene architectures
JF  - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry
N2  - A strategy to optimize the photoswitching efficiency of rigid, linear multiazobenzene constructs is presented. It consists of introducing large dihedral angles between azobenzene moieties linked via aryl-aryl connections in their para positions. Four bisazobenzenes exhibiting different dihedral angles as well as three single azobenzene reference compounds have been synthesized, and their switching behavior has been studied as well as experimentally and theoretically analyzed. As the dihedral angle between the two azobenzene units increases and consequently the electronic conjugation decreases, the photochromic characteristics improve, finally leading to individual azobenzene switches operating independently in the case of the perpendicular ortho,ortho,ortho',ortho'-tetramethyl biphenyl linker. The electronic decoupling leads to efficient separation of the absorption spectra of the involved switching states and hence by choosing the appropriate irradiation wavelength, an almost quantitative E -> Z photoisomerization up to 97% overall Z-content can be achieved. In addition, thermal Z -> E isomerization processes become independent of each other with increasing decoupling. The electronic decoupling could furthermore be proven by electrochemistry. The experimental data are supported by theory, and calculations additionally provide mechanistic insight into the preferred pathway for the thermal Z,Z -> Z,E -> E,E isomerization via inversion on the inner N-atoms. Our decoupling approach outlined herein provides the basis for constructing rigid rod architectures composed of multiple azobenzene photochromes, which display practically quantitative photoswitching properties, a necessary prerequisite to achieve highly efficient transduction of light energy directly into motion.
Y1  - 2011
U6  - https://doi.org/10.1021/jp2044114
SN  - 1520-6106
VL  - 115
IS  - 33
SP  - 9930
EP  - 9940
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Dokic, Jadranka
A1  - Gothe, Marcel
A1  - Wirth, Jonas
A1  - Peters, Maike V.
A1  - Schwarz, Jutta
A1  - Hecht, Stefan
A1  - Saalfrank, Peter
T1  - Quantum chemical investigation of thermal cis-to-trans isomerization of azobenzene derivatives : substituent effects, solvent effects, and comparison to experimental data
N2  - Quantum chemical calculations of various azobenzene (AB) derivatives have been carried out with the goal to describe the energetics and kinetics of their thermal cis -> trans isomerization. The effects of substituents, in particular their type, number, and positioning, on activation energies have been systematically studied with the ultimate goal to tailor the switching process. Trends observed for mono- and disubstituted species are discussed. A polarizable continuum model is used to study, in an approximate fashion, the cis -> trans isomerization of azobenzenes in solution. The nature of the transition state(s) and its dependence on substituents and the environment is discussed. In particular for push-pull azobenzenes, the reaction mechanism is found to change from inversion in nonpolar solvents to rotation in polar solvents. Concerning kinetics, calculations based on the Eyring transition state theory give usually reliable activation energies and enthalpies when compared to experimentally determined values. Also, trends in the resulting rate constants are correct. Other computed properties such as activation entropies and thus preexponential rate factors are in only moderate agreement with experiment.
Y1  - 2009
UR  - http://pubs.acs.org/journal/jpcafh
U6  - https://doi.org/10.1021/jp9021344
SN  - 1089-5639
ER  -