Berlin 2014 – scientific programme
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MO: Fachverband Molekülphysik
MO 21: Photochemistry
MO 21.7: Talk
Friday, March 21, 2014, 12:00–12:15, BEBEL HS213
Quantumchemical studies on the decay of photoexcited 4,4’-Dihydroxythioindigo and its methylated counterpart — •Sven Oesterling1, Marc Dittmann2, Franziska F. Graupner3, Benjamin Maerz3, Wolfgang Zinth3, Martin Engelhard2, Wolfgang Lüttke4, and Regina de Vivie-Riedle1 — 1LMU München, Dept. Chemie, München, Germany — 2MPI für Molekulare Physiologie, Dortmund, Germany — 3LMU München, Fakultät für Physik, München, Germany — 4GAU Göttingen, Fakultät für Chemie, Göttingen, Germany
The Thioindigo derivates 4,4’-Dihydroxythioindigo (DHTI) and 4,4’-Dimethoxythioindigo (DMTI) show different behaviour after photoexcitation. Both exhibit strong fluorescence, but the lifetime of the excited state of DHTI (50 ps) is roughly 200 times shorter than the one of DMTI (11 ns). Contrary to DHTI, in DMTI a cis-trans-isomerization around the central double bond can be observed, which stems from a deactivation pathway, known for thioindigo itself, too.
Our quantumchemical calculations on CASSCF/PT2 level of theory reveal a different route to reach the ground state for DHTI, mediated through an excited state intramolecular proton transfer (ESIPT). Although the corresponding conical intersection lies below the Franck-Condon energy in DMTI, too, this path is obstructed for DMTI, where, instead of a proton, a methylcation had to be transferred.
Marc Dittmann et al., Angew. Ch. Int. Ed. 2013, 52, 1-5