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 - Schmidt, Roland A1 - Hagen, Sebastian A1 - Brete, Daniel A1 - Carley, Robert A1 - Gahl, Cornelius A1 - Dokic, Jadranka A1 - Saalfrank, Peter A1 - Hecht, Stefan A1 - Tegeder, Petra A1 - Weinelt, Martin T1 - On the electronic and geometrical structure of the trans- and cis-isomer of tetra-tert-butyl-azobenzene on Au(111) N2 - Near edge X-ray absorption. ne structure and X-ray photoelectron spectroscopy have been employed to follow the reversible trans to cis isomerization of tetra-tert-butyl-azobenzene (TBA) adsorbed on Au(111). For one monolayer the molecules adopt an adsorption geometry characteristic of the trans-TBA isomer. The azo-bridge (N = N) is aligned nearly parallel to the surface and the phenyl rings exhibit a planar orientation with a small tilt angle <= 4 degrees with respect to the surface normal. Illumination of the molecular layer at 455 nm triggers the trans to cis isomerization which is associated with a pronounced change of the geometrical and electronic structure. The N1s to pi* transition of the central azo-bridge shifts by 0.45 +/- 0.05 eV to higher photon energy and the transition dipole moment (TDM) is tilted by 59 +/- 5 degrees with respect to the surface normal. The pi-system of one phenyl ring is tilted by about 30 degrees with respect to the surface normal, while the second ring plane is oriented nearly perpendicular to the surface. This reorientation is supported by a shift and broadening of the C-H resonances associated with the tert-butyl legs of the molecule. These findings support a configuration of the photo-switched TBA molecule on Au(111) which is comparable to the cis-isomer of the free molecule. In the photo-stationary state 53 +/- 5% of the TBA molecules are switched to the cis configuration. Thermal activation induces the back reaction to trans-TBA. Y1 - 2010 UR - http://pubs.rsc.org/en/content/articlehtml/2010/cp/b924409c U6 - https://doi.org/10.1039/B924409c SN - 1463-9076 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 -