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 dendrime r with 16 peryleneimide chromophores at the rim, in which the excitation wa velength is systematically varied while the detection wavelength is kept co nstant, is reported. A new setup is described which allows excitation at wa velengths 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 result s reported previously(13) which were obtained at shorter wavelengths indica ting the initial formation of a locally excited state which then evolves fu rther 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.