Ultrafast polarized fluorescence dynamics in an organic dendrimer

The excited state relaxation processes of a nitrogen-cored distyrylbenzene- stilbene (A-DSB) dendrimers and the analogous linear model compound (bis-MS B) were investigated by polarized fluorescence upconversion spectroscopy. T he fluorescence anisotropy (FA) of A-DSB was found to decay to a value clos e to zero in less than 200 fs after excitation. For the model compound bis- MSB the FA initial value was close to 0.4 and showed a relatively slow deca y (82 ps) corresponding to the overall rotational diffusion of the molecule . The results are interpreted in terms of fast transition dipole reorientat ion during relaxation of the excited states of the branched molecules. (C) 2000 American Institute of Physics. [S0003-6951(00)02334-2].