Düsseldorf 2007 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 13: Photochemistry
MO 13.4: Vortrag
Montag, 19. März 2007, 17:15–17:30, 6B
Intersystem Crossing Driven by Vibronic Spin-Orbit Coupling: A Case Study on Psoralen — •Jörg Tatchen, Martin Kleinschmidt, and Christel Marian — Institute of Theoretical Chemistry, Heinrich-Heine University, Universitätsstraße 1, D-40225 Düsseldorf
Psoralens are used in combination with UVA radiation in the treatment of several skin diseases. In order to understand the mechanisms behind the therapeutical action and undesired side effects, insight into the photophysics of psoralens is highly desirable. By means of quantum chemical methods, we investigate the mechanisms of singlet-triplet (S T) intersystem crossing (ISC) in photoexcited psoralen.
Our results [1,2,3] show that the dominant channel of S T ISC for psoralen is S1 (π → π*) T1 (π → π*) even though the corresponding spin-orbit matrix element (SOME) ⟨ S1 | HSO| T1 ⟩ at the planar S1 state equilibrium geometry is negligible. Efficient S1 T1 ISC takes place due to vibronic spin-orbit coupling which is included by a Herzberg-Teller type expansion of the coupling SOMEs. In addition, a conical intersection between the S1 and T1 state potential energy surfaces near the S1 minimum geometry brings about favorable Franck-Condon factors for the S1 T1 ISC.
References
Tatchen, J.; Kleinschmidt, M.; Marian, C. M.: J. Photochem. Photobiol. A, 167, 201-212 (2004).
Tatchen, J.; Marian, C. M.: Chem. Phys. Phys. Chem. , 8, 2133-2144 (2006).