Hannover 2010 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 15: Photochemistry II

MO 15.2: Vortrag

Mittwoch, 10. März 2010, 14:15–14:30, F 142

A Molecular Movie of Hemithioindigo Z/E-Isomerization — •Artur Nenov, Thorben Cordes, Teja Herzog, Wolfgang Zinth, and Regina de Vivie-Riedle — Ludwig-Maximilians-Universität, München, Germany

Hemithioindigo (HTI) shows a photochromic behavior due to a photoinduced Z/E-isomerization on a picosecond timescale[1]. The fast switching speed, spectral characteristics and thermal stability makes it a promising candidate for a molecular switch[2]. As both isomers exhibit different spectroscopic properties the question arises how the photochemical behavior is influenced by the molecular structure. We present a quantum chemical study of the isomerization in gas phase at CASSCF level of theory, uncovering a complex excited state (ES) decay mechanism, mediated by a number of conical intersections (CoIns). Furthermore a manifold of energetically low lying CoIns forming a seam was optimized. We could relate the variety of CoIn structures and the characteristics of the reaction to the donating and withdrawing properties of the heteroatoms. MO analysis revealed that the driving force for the ES decay can be rationalized by charge separation and recombination as postulated in the theory of weakly and strongly heterosymmetric biradicaloids[3]. The complete both-way isomerization process could be reconstructed by combining theory and experiment.

[1] T. Cordes et al., Chem. Phys. Lett., 455, 197 (2006) [2] T. Cordes et al., Chem. Phys. Lett., 428, 167, (2006) [3] J. Michl, V. Bonačić-Kouteckŷ, In Electronic Aspects of Organic Photochemistry 1990, VCH: NY