@unpublished{LambertVoelkerKochetal.2015,
  author    = {Lambert, Christoph and V{\"o}lker, Sebastian F. and Koch, Federico and Schmiedel, Alexander and Holzapfel, Marco and Humeniuk, Alexander and R{\"o}hr, Merle I. S. and Mitric, Roland and Brixner, Tobias},
  title     = {Energy Transfer Between Squaraine Polymer Sections: From helix to zig-zag and All the Way Back},
  series = {Journal of the American Chemical Society},
  journal   = {Journal of the American Chemical Society},
  doi       = {10.1021/jacs.5b03644},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-159607},
  year      = {2015},
  abstract  = {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.},
  language  = {en}
}
@unpublished{AuerhammerSchulzSchmiedeletal.2019,
  author    = {Auerhammer, Nina and Schulz, Alexander and Schmiedel, Alexander and Holzapfel, Marco and Hoche, Joscha and R{\"o}hr, Merle I. S. and Mitric, Roland and Lambert, Christoph},
  title     = {Dynamic exciton localisation in a pyrene-BODIPY-pyrene dye conjugate},
  series = {Physical Chemistry Chemical Physics},
  journal   = {Physical Chemistry Chemical Physics},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-198718},
  year      = {2019},
  abstract  = {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.},
  language  = {en}
}
@article{TurkinHolzapfelAgarwaletal.2021,
  author    = {Turkin, Arthur and Holzapfel, Marco and Agarwal, Mohit and Fischermeier, David and Mitric, Roland and Schweins, Ralf and Gr{\"o}hns, Franziska and Lambert, Christoph},
  title     = {Solvent Induced Helix Folding of Defined Indolenine Squaraine Oligomers},
  series = {Chemistry—A European Journal},
  volume    = {27},
  journal   = {Chemistry—A European Journal},
  number    = {32},
  doi       = {10.1002/chem.202101063},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256869},
  pages     = {8380-8389},
  year      = {2021},
  abstract  = {A protecting group strategy was employed to synthesise a series of indolenine squaraine dye oligomers up to the nonamer. The longer oligomers show a distinct solvent dependence of the absorption spectra, that is, either a strong blue shift or a strong red shift of the lowest energy bands in the near infrared spectral region. This behaviour is explained by exciton coupling theory as being due to H- or J-type coupling of transition moments. The H-type coupling is a consequence of a helix folding in solvents with a small Hansen dispersity index. DOSY NMR, small angle neutron scattering (SANS), quantum chemical and force field calculations agree upon a helix structure with an unusually large pitch and open voids that are filled with solvent molecules, thereby forming a kind of clathrate. The thermodynamic parameters of the folding process were determined by temperature dependent optical absorption spectra.},
  language  = {en}
}