Correlation between Ground State Conformation and Excited State Dynamics in a Multichromophoric Dendrimer Studied by Excitation Wavelength Dependent Fluorescence Upconversion

A time-resolved fluorescence upconversion study on a polyphenylene dendrimer with 16 peryleneimide chromophores at the rim, in which the excitation wavelength is systematically varied while the detection wavelength is kept constant, is reported. A new setup is described which allows excitation at wavelengths as short as 320 nm and throughout the visible range up to 900 nm with a system prompt response on the order of 300 fs. In addition to results reported previously 13 which were obtained at shorter wavelengths indicating the initial formation of a locally excited state which then evolves further into a locally excited state on a 5 ps time scale, the newly obtained data at longer wavelength excitation show the existence of a ground state interaction leading under these conditions of excitation predominantly to a directly formed complex.