title: Biphasic aggregation of a perylene bisimide dye identified by exciton-vibrational spectra.
abstract: The quantum efficiency of light emission is a crucial parameter of supramolecular aggregates that can be tuned by the molecular design of the monomeric species. Here, we report on a strong variation of the fluorescence quantum yield due to different phases of aggregation for the case of a perylene bisimide dye. In particular, a change of the dominant aggregation character from H- to J-type within the first aggregation steps is found, explaining the observed dramatic change in quantum yield. This behaviour is rationalised by means of a systematic study of the intermolecular potential energy surfaces using the time-dependent density functional based tight-binding (TD-DFTB) method. This provides a correlation between structural changes and a coupling strength and supports the notion of H-type stacked dimers and J-type stack-slipped dimers. The exciton-vibrational level structure is modelled by means of an excitonic dimer model including two effective vibrational modes per monomer. Calculated absorption and fluorescence spectra are found to be in reasonable agreement with experimental ones, thus supporting the conclusion on the aggregation behaviour.
authors.affiliation: Institut für Physik, Universität Rostock, Albert-Einstein-Str. 23-24, 18059 Rostock, Germany. oliver.kuehn@uni-rostock.de.
authors.forename: P-A
authors.initials: PA
authors.lastname: Plötz
authors.affiliation: Institut für Physik, Universität Rostock, Albert-Einstein-Str. 23-24, 18059 Rostock, Germany. oliver.kuehn@uni-rostock.de and Laboratory for Nonlinear Optics and Spectroscopy, Siberian Federal University, Svobodniy 79, 660041 Krasnoyarsk, Russia.
authors.forename: S P
authors.initials: SP
authors.lastname: Polyutov
authors.affiliation: Institut für Physik, Universität Rostock, Albert-Einstein-Str. 23-24, 18059 Rostock, Germany. oliver.kuehn@uni-rostock.de.
authors.forename: S D
authors.initials: SD
authors.lastname: Ivanov
authors.affiliation: Institut für Physik, Universität Rostock, Albert-Einstein-Str. 23-24, 18059 Rostock, Germany. oliver.kuehn@uni-rostock.de.
authors.forename: F
authors.initials: F
authors.lastname: Fennel
authors.affiliation: Institut für Physik, Universität Rostock, Albert-Einstein-Str. 23-24, 18059 Rostock, Germany. oliver.kuehn@uni-rostock.de.
authors.forename: S
authors.initials: S
authors.lastname: Wolter
authors.affiliation: Université Claude Bernard Lyon 1, CNRS, Institut Lumière Matière, F-69622, Villeurbanne, France.
authors.forename: T
authors.initials: T
authors.lastname: Niehaus
authors.affiliation: Institut für Organische Chemie & Center for Nanosystems Chemistry, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
authors.forename: Z
authors.initials: Z
authors.lastname: Xie
authors.affiliation: Institut für Physik, Universität Rostock, Albert-Einstein-Str. 23-24, 18059 Rostock, Germany. oliver.kuehn@uni-rostock.de.
authors.forename: S
authors.initials: S
authors.lastname: Lochbrunner
authors.affiliation: Institut für Organische Chemie & Center for Nanosystems Chemistry, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
authors.forename: F
authors.identifier: http://orcid.org/0000-0001-7245-0471
authors.initials: F
authors.lastname: Würthner
authors.affiliation: Institut für Physik, Universität Rostock, Albert-Einstein-Str. 23-24, 18059 Rostock, Germany. oliver.kuehn@uni-rostock.de.
authors.forename: O
authors.initials: O
authors.lastname: Kühn