Ultrafast dynamics of electronic excitations in a light-harvesting phenylacetylene dendrimer

Femtosecond degenerate pump-probe spectroscopy is used to investigate the ultrafast dynamics of electronic excitations in the nanostar dendrimer. The laser wavelength was chosen to preferentially excite the 2-ring peripheral phenylacetylene chromophores, or the 3-ring intermediate phenylacetylene chromophores. The transients reveal several components with relaxation times ranging from several hundred femtoseconds to tens of picoseconds, depending on the excitation wavelength. The experimental transients resulting from excitation of the 2-ring chromophores are interpreted in terms of Forster energy transfer, which predicts energy transfer rates that are consistent with the experimental measurements.