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  - 
TY  - JOUR
A1  - Mueller, Stefan
A1  - Lüttig, Julian
A1  - Malý, Pavel
A1  - Ji, Lei
A1  - Han, Jie
A1  - Moos, Michael
A1  - Marder, Todd B.
A1  - Bunz, Uwe H. F.
A1  - Dreuw, Andreas
A1  - Lambert, Christoph
A1  - Brixner, Tobias
T1  - Rapid multiple-quantum three-dimensional fluorescence spectroscopy disentangles quantum pathways
JF  - Nature Communications
N2  - Coherent two-dimensional spectroscopy is a powerful tool for probing ultrafast quantum dynamics in complex systems. Several variants offer different types of information but typically require distinct beam geometries. Here we introduce population-based three-dimensional (3D) electronic spectroscopy and demonstrate the extraction of all fourth- and multiple sixth-order nonlinear signal contributions by employing 125-fold (1⨯5⨯5⨯5) phase cycling of a four-pulse sequence. Utilizing fluorescence detection and shot-to-shot pulse shaping in single-beam geometry, we obtain various 3D spectra of the dianion of TIPS-tetraazapentacene, a fluorophore with limited stability at ambient conditions. From this, we recover previously unknown characteristics of its electronic two-photon state. Rephasing and nonrephasing sixth-order contributions are measured without additional phasing that hampered previous attempts using noncollinear geometries. We systematically resolve all nonlinear signals from the same dataset that can be acquired in 8 min. The approach is generalizable to other incoherent observables such as external photoelectrons, photocurrents, or photoions.
KW  - Atomic and molecular interactions with photons
KW  - Optical spectroscopy
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-202529
VL  - 10
ER  -