Send to

Choose Destination
See comment in PubMed Commons below
Photochem Photobiol Sci. 2009 Dec;8(12):1655-66. doi: 10.1039/b9pp00022d. Epub 2009 Oct 7.

The photophysics of alloxazine: a quantum chemical investigation in vacuum and solution.

Author information

Institute of Theoretical and Computational Chemistry, Heinrich Heine University Düsseldorf, Universitätsstr. 1, D-40225, Düsseldorf, Germany.


(Time-dependent) Kohn-Sham density functional theory and a combined density functional/multi-reference configuration interaction method (DFT/MRCI) were employed to explore the ground and low-lying electronically excited states of alloxazine, a flavin related molecule. Spin-orbit coupling was taken into account using an efficient, nonempirical mean-field Hamiltonian. Intersystem crossing (ISC) rate constants for S --> T transitions were computed, employing both direct and vibronic spin-orbit coupling. Solvent effects were mimicked by a conductor-like screening model and micro-hydration with up to six explicit water molecules. Multiple minima were found on the first excited singlet (S(1)) potential energy hypersurface (PEH) with electronic structures (1)(npi*) and (1)(pipi*), corresponding to the dark 1 (1)A'' (S(1)) state and the nearly degenerate, optically bright 2 (1)A' (S(2)) state in the vertical absorption spectrum, respectively. In the vacuum the minimum of the (1)(npi*) electronic structure is clearly found below that of the (1)(pipi*) electronic structure. Population transfer from (1)(pipi*) to (1)(npi*) may proceed along an almost barrierless pathway. Hence, in the vacuum, internal conversion (IC) between the 2 (1)A' and the 1 (1)A'' state is expected to be ultrafast and fluorescence should be quenched completely. The depletion of the (1)(npi*) state is anticipated to occur via competing IC and direct ISC processes. In aqueous solution this changes, due to the blue shift of the (1)(npi*) state and the red shift of the (1)(pipi*) state. However, the minimum of the (1)(npi*) state still is expected to be found on the S(1) PEH. For vibrationally relaxed alloxazines pronounced fluorescence and ISC by a vibronic spin-orbit coupling mechanism is expected. At elevated temperatures or excess energy of the excitation laser, the (1)(npi*) state is anticipated to participate in the deactivation process and to partially quench the fluorescence.

PubMed Commons home

PubMed Commons

How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for Royal Society of Chemistry
    Loading ...
    Support Center