TY  - JOUR
A1  - Brixner, Tobias
A1  - Koch, Federico
A1  - Kullmann, Martin
A1  - Selig, Ulrike
A1  - Nuernberger, Patrick
A1  - Götz, Daniel C. G.
A1  - Bringmann, Gerhard
T1  - Coherent two-dimensional electronic spectroscopy in the Soret band of a chiral porphyrin dimer
JF  - New Journal of Physics
N2  - Using coherent two-dimensional (2D) electronic spectroscopy in fully noncollinear geometry, we observe the excitonic coupling of β,β'-linked bis[tetraphenylporphyrinato-zinc(II)] on an ultrafast timescale in the excited state. The results for two states in the Soret band originating from an excitonic splitting are explained by population transfer with approximately 100 fs from the energetically higher to the lower excitonic state. This interpretation is consistent with exemplary calculations of 2D spectra for a model four-level system with coupling.
KW  - optics
KW  - quantum optics
KW  - laser
Y1  - 2013
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-96139
ER  - 
TY  - JOUR
A1  - Dostál, Jakub
A1  - Fennel, Franziska
A1  - Koch, Federico
A1  - Herbst, Stefanie
A1  - Würthner, Frank
A1  - Brixner, Tobias
T1  - Direct observation of exciton–exciton interactions
JF  - Nature Communications
N2  - Natural light harvesting as well as optoelectronic and photovoltaic devices depend on efficient transport of energy following photoexcitation. Using common spectroscopic methods, however, it is challenging to discriminate one-exciton dynamics from multi-exciton interactions that arise when more than one excitation is present in the system. Here we introduce a coherent two-dimensional spectroscopic method that provides a signal only in case that the presence of one exciton influences the behavior of another one. Exemplarily, we monitor exciton diffusion by annihilation in a perylene bisimide-based J-aggregate. We determine quantitatively the exciton diffusion constant from exciton–exciton-interaction 2D spectra and reconstruct the annihilation-free dynamics for large pump powers. The latter enables for ultrafast spectroscopy at much higher intensities than conventionally possible and thus improves signal-to-noise ratios for multichromophore systems; the former recovers spatio–temporal dynamics for a broad range of phenomena in which exciton interactions are present.
KW  - energy transfer
KW  - self-assembly
KW  - optical spectroscopy
Y1  - 2018
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-226271
VL  - 9
ER  - 
TY  - INPR
A1  - Lambert, Christoph
A1  - Völker, Sebastian F.
A1  - Koch, Federico
A1  - Schmiedel, Alexander
A1  - Holzapfel, Marco
A1  - Humeniuk, Alexander
A1  - Röhr, Merle I. S.
A1  - Mitric, Roland
A1  - Brixner, Tobias
T1  - Energy Transfer Between Squaraine Polymer Sections: From helix to zig-zag and All the Way Back
T2  - Journal of the American Chemical Society
N2  - Joint experimental and theoretical study of the absorption spectra of squaraine polymers in solution provide evidence that two different conformations are present in solution: a helix and a zig-zag structure. This unique situation allows investigating ultrafast energy transfer processes between different structural segments within a single polymer chain in solution. The understanding of the underlying dynamics is of fundamental importance for the development of novel materials for light-harvesting and optoelectronic applications. We combine here femtosecond transient absorption spectroscopy with time-resolved 2D electronic spectroscopy showing that ultrafast energy transfer within the squaraine polymer chains proceeds from initially excited helix segments to zig-zag segments or vice versa, depending on the solvent as well as on the excitation wavenumber. These observations contrast other conjugated polymers such as MEH-PPV where much slower intrachain energy transfer was reported. The reason for the very fast energy transfer in squaraine polymers is most likely a close matching of the density of states between donor and acceptor polymer segments because of very small reorganization energy in these cyanine-like chromophores.
KW  - energy transfer dynamics
KW  - squaraine polymer
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-159607
UR  - http://dx.doi.org/10.1021/jacs.5b03644
N1  - This document is the unedited Author's version of a Submitted Work that war subsequently accepted for publication in Journal of the American Chemical Society, copyright American Chemical Society after peer review. To access the final edited and published work see doi:10.1021/jacs.5b03644.
ER  -