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

Abstract

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.