Energy Transfer within Zn-Porphyrin Dendrimers: Study of the Singlet−Singlet Annihilation Kinetics

In this article, we explore energy transfer processes within a series of Zn-porphyrin-appended dendrimers by means of excitation intensity dependent transient absorption measurements. We report singlet-singlet annihilation on two distinct time scales of 18 +/- 5 ps and 130 +/- 10 ps in the dimer and the dendrimers. The two distinct processes reflect the presence of two structural conformer distributions. Analysis of the singlet-singlet annihilation transient kinetics shows that sequential annihilation occurs within subunits up to four Zn-porphyrins in the dendrimers. The onset of the singlet-singlet annihilation process depending on the size of the molecule reveals a difference in the number of communicating Zn-porphyrins. We further report a full characterization of the transient absorption kinetics of the monomer over a spectral range from 450 to 730 nm.