title: Energy Transfer Between Squaraine Polymer Sections: From Helix to Zigzag and All the Way Back.
abstract: We provide a joint experimental and theoretical study of squaraine polymers in solution. The absorption spectra show evidence that two different conformations are present in the polymer: a helix and a zigzag 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. Here, we combine femtosecond transient absorption spectroscopy with time-resolved 2D electronic spectroscopy in order to demonstrate that ultrafast energy transfer within the squaraine polymer chains proceeds from initially excited helix segments to zigzag 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 the very small reorganization energy in these cyanine-like chromophores.
authors.affiliation: †Institut für Organische Chemie, ‡Center for Nanosystems Chemistry (CNC), and §Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Lambert
authors.affiliation: †Institut für Organische Chemie, ‡Center for Nanosystems Chemistry (CNC), and §Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
authors.forename: Federico
authors.initials: F
authors.lastname: Koch
authors.affiliation: †Institut für Organische Chemie, ‡Center for Nanosystems Chemistry (CNC), and §Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
authors.forename: Sebastian F
authors.initials: SF
authors.lastname: Völker
authors.affiliation: †Institut für Organische Chemie, ‡Center for Nanosystems Chemistry (CNC), and §Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Schmiedel
authors.affiliation: †Institut für Organische Chemie, ‡Center for Nanosystems Chemistry (CNC), and §Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
authors.forename: Marco
authors.initials: M
authors.lastname: Holzapfel
authors.affiliation: †Institut für Organische Chemie, ‡Center for Nanosystems Chemistry (CNC), and §Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Humeniuk
authors.affiliation: †Institut für Organische Chemie, ‡Center for Nanosystems Chemistry (CNC), and §Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
authors.forename: Merle I S
authors.initials: MI
authors.lastname: Röhr
authors.affiliation: †Institut für Organische Chemie, ‡Center for Nanosystems Chemistry (CNC), and §Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
authors.forename: Roland
authors.initials: R
authors.lastname: Mitric
authors.affiliation: †Institut für Organische Chemie, ‡Center for Nanosystems Chemistry (CNC), and §Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Brixner