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Photochemical Z-->E isomerization of a hemithioindigo/hemistilbene omega-amino acid
Thorben Cordes1, Björn Heinz, Nadja Regner
1Lehrstuhl für BioMolekulare Optik, Department für Physik, Ludwig-Maximilians-Universität, Oettingenstr. 67, 80538 München, Germany.
Abstract:
The molecule HTI, which combines hemithioindigo and hemistilbene molecular parts, allows reversible switching between two isomeric states. Photochromic behaviour of the HTI molecule is observed by irradiation with UV/Vis light. The photochemical reaction, a Z/E isomerization around the central double bond connecting the two molecular parts, is investigated by transient absorption and emission spectroscopy. For a special HTI molecule, namely, an omega-amino acid, the Z-->E isomerization process occurs on a timescale of 30 ps. In the course of the reaction fast processes on the 1-10 ps timescale are observed which point to motions of the molecule on the potential-energy surface of the excited state. The combination of transient absorption experiments in the visible spectral range with time-resolved fluorescence and infrared measurements reveal a photochemical pathway with three intermediate states. Together with a theoretical modelling procedure the experiments point to a sequential reaction scheme and give indications of the nature of the involved intermediates.
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