Incorporation of the trimethoxyphenyl group at position 7 of flavin can drastically change the photophysical properties of flavin. We show unique fast singlet (π,π*) excited state deactivation pathway through nonadiabatic transition to the (n,π*) excited- state, and subsequent deactivation to the ground electronic state (S), closing the photocycle. This mechanism explains the exceptionally weak fluorescence and the short excited-state lifetime for the flavin trimethoxyphenyl derivative and the lack of excited triplet T state formation. Full recovery of flavin in its ground state takes place within a 15 ps time window after photoexcitation in a polar solvent such as acetonitrile. According to quantum chemical calculations, the C-O distance elongates by 0.16 Å in the (n,π*) state, with respect to the ground state. Intermediate-state structures are predicted by theoretical ab initio calculations and their dynamics are investigated using broadband vis-NIR time-resolved transient absorption and fluorescence up-conversion techniques.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC11487251PMC
http://dx.doi.org/10.1038/s41598-024-75239-xDOI Listing

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