Femtosecond luminescence dynamics in a nonlinear optical organic dendrimer

The ultrafast intrinsic dynamics of an organic dendrimer in solution and in a thin film is reported using fluorescence upconversion spectroscopy. Femt osecond decay is detected at higher emission energies, while at lower energ ies a fluorescence rise time (similar to 3 ps) was observed that is depende nt on the solvent's polarity. A strong excitation energy dependence of the decay pattern was also observed. Different synthetic functional groups that comprise the macromolecular dendrimer structure were investigated. The mec hanism, which describes the complex dynamics in the dendrimer system, was f ound to be associated with the excitation of the attached chromophore nitro aminostilbene. These results indicate the absence of excited-state interact ions of functional groups within the dendrimer macromolecule. A model, whic h includes the existence of an intermediate nonradiative state, is proposed to describe the complex ultrafast fluorescence dynamics in the dendrimer s ystem.