title: Structural relaxation in the singlet excited state of star-shaped oligofluorenes having a truxene or isotruxene as a core.
abstract: Oligofluorenes attract wide attention due to their excellent fluorescent properties. For the detailed understanding of the excited state properties, ultrafast processes have to be clarified. Here, we have investigated the structural relaxation in the singlet excited state of star-shaped oligofluorenes with a truxene or isotruxene core, to which oligofluorenes (n = 1-4) were attached. The transient absorption peak showed red-shift with time upon excitation. The fluorescence decay profiles in the picosecond domain showed the fast component in addition to the component corresponding to the singlet excited state lifetime. These ultrafast phenomena can be attributed to the structural relaxation, i.e., planarization, in the singlet excited state. The planarization process was supported by the theoretical calculation based on the time-dependent density functional theory. Furthermore, dependence of two-photon absorption cross section on the core of the star-shaped oligofluorene has been elucidated.
authors: The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan. fuji@sanken.osaka-u.ac.jp
authors: Mamoru
authors: M
authors: Fujitsuka
authors: Dae Won
authors: DW
authors: Cho
authors: Hsin-Hau
authors: HH
authors: Huang
authors: Jye-Shane
authors: JS
authors: Yang
authors: Tetsuro
authors: T
authors: Majima