title: Unraveling excited-state dynamics in a polyfluorene-perylenediimide copolymer.
abstract: Insight into the exciton dynamics occurring in a polyfluorene-perylenediimide (PF-PDI) copolymer with a reaction mixture ratio of 100 fluorene units to 1 N,N'-bis(phenyl)-1,6,7,12-tetra(p-tert-octylphenoxy)-perylene-3,4,9,10-tetracarboxylic acid diimide (PDI) is presented here. Time-correlated single photon counting and femtosecond transient absorption spectroscopy measurements on the PF-PDI copolymer have been employed to investigate the excited-state properties of the polyfluorene subunit where the exciton is localized (PF) and the incorporated PDI chromophore. The experimental results were compared with those obtained from a polyfluorene polymer (model PF) and a N,N'-bis(2,6-diisopropylphenyl)-1,6,7,12-tetra(p-tert-octylphenoxy)-perylene-3,4,9,10-tetracarboxylic acid diimide (model PDI) which were used as reference compounds. Because of the high polydispersity of the PF-PDI copolymer, there is a polymer fraction present that contains no PDI chromophores (polyfluorene polymer fraction (PF polymer fraction)), and wide-field imaging of single polymers chains of the synthesized PF-PDI copolymer was used to estimate this PF polymer fraction. Following the primary excitation of the PF in the PF-PDI copolymer, energy hopping between PF's can occur. A fraction of the energy of the absorbed photons will be transferred to a PDI chromophore via energy transfer from a PF. In a polar solvent, a charge transfer state having the S(1) of the PDI moiety as a precursor state is found to form with high efficiency on a nanosecond time scale. The data suggest that a fraction of the absorbed energy is directed, transferred, and used in charge separation, providing a clear view of a multistep mechanism of exciton dissociation into charges.
authors.affiliation: Department of Chemistry and Institute for Nanoscale Physics and Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200F, 3001 Heverlee, Belgium.
authors.forename: Eduard
authors.initials: E
authors.lastname: Fron
authors.forename: Ania
authors.initials: A
authors.lastname: Deres
authors.forename: Susana
authors.initials: S
authors.lastname: Rocha
authors.forename: Gang
authors.initials: G
authors.lastname: Zhou
authors.forename: Klaus
authors.initials: K
authors.lastname: Müllen
authors.forename: Frans C
authors.initials: FC
authors.lastname: De Schryver
authors.forename: Michel
authors.initials: M
authors.lastname: Sliwa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Uji-i
authors.forename: Johan
authors.initials: J
authors.lastname: Hofkens
authors.forename: Tom
authors.initials: T
authors.lastname: Vosch