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

Content Provider	Royal Society of Chemistry (RSC)
Author	Marian, Christel M. Salzmann, Susanne
Copyright Year	2009
Abstract	(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 ST 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 (S1) potential energy hypersurface (PEH) with electronic structures 1(nπ) and 1(ππ), corresponding to the dark 1 1A″ (S1) state and the nearly degenerate, optically bright 2 1A′ (S2) state in the vertical absorption spectrum, respectively. In the vacuum the minimum of the 1(nπ) electronic structure is clearly found below that of the 1(ππ) electronic structure. Population transfer from 1(ππ) to 1(nπ) may proceed along an almost barrierless pathway. Hence, in the vacuum, internal conversion (IC) between the 2 1A′ and the 1 1A″ state is expected to be ultrafast and fluorescence should be quenched completely. The depletion of the 1(nπ) 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(nπ) state and the red shift of the 1(ππ) state. However, the minimum of the 1(nπ) state still is expected to be found on the S1 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(nπ*) state is anticipated to participate in the deactivation process and to partially quench the fluorescence.
Starting Page	1655
Ending Page	1666
Page Count	12
File Format	HTM / HTML PDF
ISSN	1474905X
Volume Number	8
Issue Number	12
Journal	Photochemical & Photobiological Sciences
DOI	10.1039/b9pp00022d
Language	English
Publisher	Royal Society of Chemistry
Access Restriction	Open
Subject Keyword	Atari ST Absorption spectroscopy Hypersurface Multireference configuration interaction Molecular Hamiltonian Fluorescence Kohn Configuration interaction Potential energy surface Population transfer PEH Blueshift Laser ISC Density functional theory Intersystem crossing Internal conversion Spin\u2013orbit interaction
Content Type	Text
Resource Type	Article
Subject	Physical and Theoretical Chemistry

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