TY  - INPR
A1  - Auerhammer, Nina
A1  - Schulz, Alexander
A1  - Schmiedel, Alexander
A1  - Holzapfel, Marco
A1  - Hoche, Joscha
A1  - Röhr, Merle I. S.
A1  - Mitric, Roland
A1  - Lambert, Christoph
T1  - Dynamic exciton localisation in a pyrene-BODIPY-pyrene dye conjugate
T2  - Physical Chemistry Chemical Physics
N2  - The photophysics of a molecular triad consisting of a BODIPY dye and two pyrene chromophores attached in 2-position are investigated by steady state and fs-time resolved transient absorption spectroscopy as well as by field induced surface hopping (FISH) simulations. While the steady state measurements indicate moderate chromophore interactions within the triad, the time resolved measurements show upon pyrene excitation a delocalised excited state which localises onto the BODIPY chromophore with a time constant of 0.12 ps. This could either be interpreted as an internal conversion process within the excitonically coupled chromophores or as an energy transfer from the pyrenes to the BODIPY dye. The analysis of FISH-trajectories reveals an oscillatory behaviour where the excitation hops between the pyrene units and the BODIPY dye several times until finally they become localised on the BODIPY chromophore within 100 fs. This is accompanied by an ultrafast nonradiative relaxation within the excitonic manifold mediated by the nonadiabatic coupling. Averaging over an ensemble of trajectories allowed us to simulate the electronic state population dynamics and determine the time constants for the nonradiative transitions that mediate the ultrafast energy transfer and exciton localisation on BODIPY.
KW  - Exciton localization dynamics
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-198718
UR  - https://doi.org/10.1039/C9CP00908F
N1  - Accepted manuscript
ER  - 
TY  - INPR
A1  - Humeniuk, Alexander
A1  - Bužančić, Margarita
A1  - Hoche, Joscha
A1  - Cerezo, Javier
A1  - Mitric, Roland
A1  - Santoro, Fabrizio
A1  - Bonačić-Koutecky, Vlasta
T1  - Predicting fluorescence quantum yields for molecules in solution: A critical assessment of the harmonic approximation and the choice of the lineshape function
T2  - The Journal of Chemical Physics
N2  - For the rational design of new fluorophores, reliable predictions of fluorescence quantum yields from first principles would be of great help. However, efficient computational approaches for predicting transition rates usually assume that the vibrational structure is harmonic. While the harmonic approximation has been used successfully to predict vibrationally resolved spectra and radiative rates, its reliability for non-radiative rates is much more questionable. Since non-adiabatic transitions convert large amounts of electronic energy into vibrational energy, the highly excited final vibrational states deviate greatly from harmonic oscillator eigenfunctions. We employ a time-dependent formalism to compute radiative and non-radiative rates for transitions and study the dependence on model parameters. For several coumarin dyes we compare different adiabatic and vertical harmonic models (AS, ASF, AH, VG, VGF, VH), in order to dissect the
importance of displacements, frequency changes and Duschinsky rotations. In addition we analyze the effect of different broadening functions (Gaussian, Lorentzian or Voigt). Moreover, to assess the qualitative influence of anharmonicity on the internal conversion rate, we develop a simplified anharmonic model. We adress the reliability of these models considering the potential errors introduced by the harmonic approximation and the phenomenological width of the broadening function.
KW  - fluorescence quantum yield
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-199305
UR  - https://doi.org/10.1063/1.5143212
N1  - Accepted Manuscript.
N1  - This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in A. Humeniuk et al. J. Chem. Phys. 152, 054107 (2020); https://doi.org/10.1063/1.5143212 and may be found at https://doi.org/10.1063/1.5143212.
ER  -