Supramolecular porphyrin assemblies through amidinium-carboxylate salt bridges and fast intra-ensemble excited energy transfer

Well-defined supramolecular assemblies of Zn and free-base porphyrins are constructed through the formation of amidinium-carboxylate salt bridges. A one-to-one donor-acceptor pair and a four-to-one antenna-type assembly are investigated. The steady-state and time-resolved fluorescence measurements unequivocally showed that efficient singlet-singlet excited energy transfer from the Zn-porphyrin complex to the free-base porphyrin takes place in these assemblies. Indeed, the observed energy-transfer rates in both types of assemblies are much faster than those the Förster mechanism would suggest, implying the involvement of an intermolecular through-bond mechanism.