Spectroscopic evidence for excitonic localization in fractal antenna supermolecules

Direct experimental evidence is presented for the existence of localized excitations on fractal supermolecular structures that may serve as photonic antenna systems. For one dendrimer family the electronic spectra show no redshift with system size, indicating that the excitations are localized at the nodes of the Cayley trees describing these ordered structures. In contrast, similar dendrimers with varying lengths of the molecular branches exhibit a decrease in the band edge energy with a growing size of the system, consistent with a hierarchy of localization lengths. The latter corresponds to an energy funnel property of these ordered nanostructures.