Research Highlights: 2013
C. Gahl, D. Brete, F. Leyssner, M. Koch, E. McNellis, J. Mielke, R. Carley, L. Grill, K. Reuter, P. Tegeder, and M. Weinelt
Coverage- and Temperature-Controlled Isomerization of an Imine Derivative on Au(111)
Journal of the American Chemical Society 135, 4273 (2013)
Abstract. The isomerization behavior of photochromic molecular switches is strongly influenced by adsorption on metal surfaces. For (E)-3,5-di-tert-butyl-N-(3,5-di-tert-butylbenzylidene)aniline (abbreviated as TBI for tetra-tert-butyl imine) it is found that a layer adsorbed on Au(111) can undergo an isomerization from the trans- to the cis- and back to the trans-configuration when continuously increasing the sample temperature and accordingly decreasing the sample coverage. The conformation and adsorption geometry of TBI are determined from near-edge X-ray absorption fine structure measurements in agreement with density-functional-theory calculations taking into account the van der Waals interaction between adsorbate and metal surface. The coverage- and temperature-controlled conformational transitions are reversible and are driven by the higher packing density of the less stable cis-isomer in combination with the low thermal activation barrier of the trans to cis isomerization typical for imine derivatives. This unexpected scenario is corroborated by thermal desorption and vibrational spectroscopy, as well as scanning tunneling microscopy.
Mentioned in Angewandte Chemie 125, 826 (2013) as a high class contribution.
Slow relaxation: Exergonic high-spin→low-spin relaxation after photoexcitation has been found to be exceedingly slow in a class of iron(II) complexes with hexadentate imine ligands. The thermal activation barriers that arise between the quintet- and singlet-spin manifolds are the highest ever recorded for spin crossover of isolated molecules in free solution (see figure).
Abstract. Creating photoactive monolayers of photochromes is of considerable technological interest. This paper describes the construct of fulgimide monolayers on silicon surfaces and presents a quantitative IR analysis studies of their composition and switching properties. The scheme on top shows the structure of the starting C-form terminated Si(111) surface and the graph below sketches the surface composition at the photostationnary states under visisble and UV irradiation, as derived from in situ IR spectroscopy after several UV/vis irradiation cycles.
The editorial can be found here.