Tuning electron transfer in supramolecular nano-architectures made of fullerenes and porphyrins

The current work focuses on self-assembled nano-architectures in which metal–ligand coordination between a zinc tetraphenyl-porphyrin (ZnP) and a zinc tetrakis(4-((1,3-dithiol-2-ylidene)methyl)phenyl)-porphyrin (ZnP-TDP), as electron donors, and functionalized fullerenes (C60) featuring different conjugated pyridine substituents as electron acceptors have been designed and investigated. Stoichiometric ratios and binding constants were derived from absorption and fluorescence measurements. Important insight into the free-energy change of charge separation and recombination was obtained from differential pulse voltammetry studies. Compelling evidence for energy transfer, charge separation and recombination was obtained from femtosecond and nanosecond transient-absorption measurements in a wide temperature range. Intramolecular energy transfer is found to take place from TDP to ZnP followed by intramolecular charge transfer from ZnP to C60. Semiempirical and density-functional theory calculations were used to help understand the excited-state deactivation mechanisms.