Mainz 2017 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 1: Photochemistry
MO 1.2: Vortrag
Montag, 6. März 2017, 15:00–15:15, N 6
Photocleavage of coumarin dimers studied by uv ultrafast transient absorption spectroscopy — •Man Jiang1, Nicholas Paul1, Nikolai Bieniek2, Tiago Buckup1, Norbert Hampp2, and Marcus Motzkus1 — 1Institute of Physical Chemistry, Im Neuenheimer Feld 229, University of Heidelberg, D-69120 Heidelberg — 2Department of Chemistry, Hans-Meerwein-Str. 4, University of Marburg, D-35032 Marburg
The photoinduced cleavage of a coumarin dimer into its two monomers is a promising mechanism for laser controlled medical applications. In order to understand the underlying dynamics of the cleavage reaction in details and develop strategies for an increase of the reaction efficiency, UV transient absorption spectroscopy was applied to three unsubstituted coumarin dimer isomers, the anti-head-to-head dimer, the syn-head-to-head dimer and the syn-head-to-tail dimer. The experiments performed under 280 nm pumping and broadband (300-650 nm) probing reveal that the cleavage reaction of coumarin dimers occurs via non-radiative short-lived singlet states. Two branched kinetic models were developed, which describe the formation of monomers and relaxation dynamics of dimers, from which we were able to explore the precise time-scale of coumarin monomers formation and the quantum yields of the dimer splitting. The anti-hh dimer shows the highest cleavage efficiency with a value of about 20 %. The differences of cleavage efficiency for three dimer isomers are interpreted in terms of different steric hindrances of substitution groups attached to the cyclobutane ring and charge delocalization on the intermediate state.