@article{WeigelDobryakovKlaumuenzeretal.2011,
  author    = {Weigel, A. and Dobryakov, A. and Klaum{\"u}nzer, Bastian and Sajadi, M. and Saalfrank, Peter and Ernsting, N. P.},
  title     = {Femtosecond stimulated raman spectroscopy of flavin after optical excitation},
  series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry},
  volume    = {115},
  journal   = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry},
  number    = {13},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1520-6106},
  doi       = {10.1021/jp1117129},
  pages     = {3656 -- 3680},
  year      = {2011},
  abstract  = {In blue-light photoreceptors using flavin (BLUF), the signaling state is formed already within several 100 ps after illumination, with only small changes of the absorption spectrum. The accompanying structural evolution can, in principle, be monitored by femtosecond stimulated Raman spectroscopy (FSRS). The method is used here to characterize the excited-state properties of riboflavin and flavin adenine dinucleotide in polar solvents. Raman modes are observed in the range 90-1800 cm(-1) for the electronic ground state S-0 and upon excitation to the S-1 state, and modes >1000 cm(-1) of both states are assigned with the help of quantum-chemical calculations. Line shapes are shown to depend sensitively on resonance conditions. They are affected by wavepacket motion in any of the participating electronic states, resulting in complex amplitude modulation of the stimulated Raman spectra. Wavepackets in S-1 can be marked, and thus isolated, by stimulated-emission pumping with the picosecond Raman pulses. Excited-state absorption spectra are obtained from a quantitative comparison of broadband transient fluorescence and absorption. In this way, the resonance conditions for FSRS are determined. Early differences of the emission spectrum depend on excess vibrational energy, and solvation is seen as dynamic Stokes shift of the emission band. The ne state is evidenced only through changes of emission oscillator strength during solvation. S-1 quenching by adenine is seen with all methods in terms of dynamics, not by spectral intermediates.},
  language  = {en}
}
@article{KlaumuenzerKroenerLischkaetal.2012,
  author    = {Klaum{\"u}nzer, Bastian and Kr{\"o}ner, Dominik and Lischka, Hans and Saalfrank, Peter},
  title     = {Non-adiabatic excited state dynamics of riboflavin after photoexcitation},
  series = {Physical chemistry, chemical physics : a journal of European Chemical Societies},
  volume    = {14},
  journal   = {Physical chemistry, chemical physics : a journal of European Chemical Societies},
  number    = {24},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {1463-9076},
  doi       = {10.1039/c2cp40978j},
  pages     = {8693 -- 8702},
  year      = {2012},
  abstract  = {Flavins are chromophores in light-gated enzymes and therefore central in many photobiological processes. To unravel the optical excitation process as the initial, elementary step towards signal transduction, detailed ultrafast (femtosecond) experiments probing the photo-activation of flavins have been carried out recently [Weigel et al., J. Phys. Chem. B, 2011, 115, 3656-3680.]. The present paper contributes to a further understanding and interpretation of these experiments by studying the post-excitation vibrational dynamics of riboflavin (RF) and microsolvated riboflavin, RF center dot 4H(2)O, using first principles non-adiabatic molecular dynamics. By analyzing the characteristic atom motions and calculating time-resolved stimulated emission spectra following pi pi* excitation, it is found that after optical excitation C-N and C-C vibrations in the isoalloxazine rings of riboflavin set in. The Franck-Condon (vertically excited) state decays within about 10 fs, in agreement with experiment. Anharmonic coupling leads to Intramolecular Vibrational energy Redistribution (IVR) on the timescale of about 80-100 fs, first to (other) C-C stretching modes of the isoalloxazine rings, then by energy spread over the whole molecule, including low-frequency in-plane modes. The IVR is accompanied by a red-shift and broadening of the emission spectrum. When RF is microsolvated with four water molecules, an overall redshift of optical spectra by about 20 nm is observed but the relaxation dynamics is only slightly affected. For several trajectories, a tendency for hydrogen transfer from water to flavin-nitrogen (N-5) was found.},
  language  = {en}
}
@article{KlaumuenzerKroener2009,
  author    = {Klaum{\"u}nzer, Bastian and Kroener, Dominik},
  title     = {N-Inversion in 2-azabicyclopentane derivatives : model simulations for a laser controlled molecular switch},
  issn      = {1144-0546},
  doi       = {10.1039/B812319e},
  year      = {2009},
  abstract  = {We report model quantum simulations for the nitrogen inversion in 2-azabicyclo[1.1.1] pentane derivates controlled by laser pulses proposing to use this class of molecules as molecular switches. The derivatives trans-5- fluoro-2-methyl-2-azabicyclo[1.1.1] pentane and cis-5-fluoro-2-methyl-2-azabicyclo[1.1.1] pentane are investigated by means of density functional theory and quantum wave packet dynamics. The molecules have two stable, i.e. energetically well-separated, conformers along the N-inversion coordinate. In 1D model simulations the transformation from one conformer to the other is accomplished in the electronic ground state by using two overlapping chirped linearly polarized IR laser pulses for the trans-and cis-isomer or alternatively via an electronic excited state employing a pump- dump sequence of ultrashort UV laser pulses.},
  language  = {en}
}