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"The Hammett Relationship and Reactions in the Excited Electronic State: Hemithioindigo Z/E-Photoisomerization" T. Cordes, T. Schadendorf, B. Priewisch, K. Rück-Braun, and W. ZinthThe Journal of Physical Chemistry A 112 (2008) 581-588 Abstract: The photochemical reaction dynamics of a set of photochromic compounds based on thioindigo and stilbene molecular parts (hemithioindigos, HTI) are presented. Photochemical Z/E-isomerization around the central double bond occurs with time constants of 216 ps (Z to E) and 10 ps (E to Z) for a 5-methyl-hemithioindigo. Chemical substitution on the stilbene moiety causes unusually strong changes in the reaction rate. Electrondonating substituents in the position para to the central double bond (e.g., para-methoxy) strongly accelerate the reaction, while the reaction is drastically slowed by electron-withdrawing groups in this position (e.g., para-nitrile). We correlate the experimental data of seven HTI-compounds in a quantitative manner using the Hammett equation and present a qualitative explanation for the application of ground-state Hammett constants to describe the photoisomerization reaction. BMO authors (in alphabetic order): Thorben Cordes Wolfgang Zinth Assoziierte Projekte: Photoisomerizations  WWW-Version |