Düsseldorf 2007 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 11: Biomolecules

MO 11.2: Vortrag

Montag, 19. März 2007, 14:15–14:30, 6B

The Photophysics of 10-Methylisoalloxazine: A Quantum Chemical Investigation — •Susanne Salzmann and Christel Marian — Institute of Theoretical Chemistry and SFB663, Heinrich Heine Universität Düsseldorf, Universitätsstr. 1, 40225 Düsseldorf, Germany

In recent years flavins have recieved growing attention due to their decisive role as cofactors in phototropins. In the LOV (light, oxygen, and voltage sensitive) domain of the blue light receptor the primary step after light absorption involves a rapid decay of the excited singlet state to the lowest excited triplet state via an intersystem crossing (ISC) mechanism. In aqueous solution, the free flavin shows a different behaviour, the ISC efficiency decreases and the fluorescence increases in comparison to the LOV domain.

Vertical and adiabatic electronic spectra of 10-methylisoalloxazine have been investigated by means of combined density functional and multi-reference configuration interaction methods. Spectral shifts due to electrostatic interactions in aqueous solution are taken into account employing the conductor-like screening model. Spin-orbit interaction has been computed involving a nonempirical mean-field approach. On the basis of these calculations, we suggest that in the LOV domain the ISC takes place between the excited ¹(π → π^*) state (S₁) and the ³(n → π^*) state (T₂). In aqueous solution this ISC channel is not accessible due to the blue shift of the ³(n → π^*) state.