title: Dendritic metalloporphyrin-fullerene conjugates: changing the microenvironment around redox-active centers and its impact on charge-transfer reactions.
abstract: Photophysical investigations on a series of (2,4,6)-tris-substituted metalloporphyrin-fullerene conjugates revealed the effects of an electron-rich microenvironment surrounding the electron-donating porphyrin as a function of the metal center. On one hand, for all conjugates-water-soluble and non-water-soluble-ultrafast charge separation was observed upon photoexcitation. On the other hand, when examining the charge recombination dynamics for the non-water-soluble conjugates it becomes obvious that the (2,4,6)-tris-substitution stabilizes the radical-ion-pair state relative to the mono-substitution in the ortho-, meta-, and para-position. The more efficient protection of the electron-donating porphyrin from solvation is thought to be the major cause for this impact. Nevertheless, the situation is slightly different for the water-soluble conjugates. At first glance, the radical-ion-pair state lifetimes are, also in the case of the (2,4,6)-tris-substitution, longer than for the mono-substituted ortho-, meta- and para-conjugates. Upon closer inspection, they fail, however, to exhibit any metal dependence. Competing with the protection from solvation of the dendrons, dipole-charge interactions impact the stabilization in the polar aqueous environment and, in turn, become the dominant force governing the electron-transfer dynamics.
authors: Department of Chemistry and Pharmacy and Interdisciplinary Center of Molecular Materials (ICMM), Friedrich-Alexander Universität Erlangen Nürnberg, Egerlandstrasse 3, 91058 Erlangen, Germany.
authors: Evangelos
authors: E
authors: Krokos
authors: Fabian
authors: F
authors: Spänig
authors: Michaela
authors: M
authors: Ruppert
authors: Andreas
authors: A
authors: Hirsch
authors: Dirk M
authors: DM
authors: Guldi
mesh_terms: D050091:Dendrimers / Q000737:chemistry; D037741:Fullerenes / Q000737:chemistry*; D017136:Ion Transport; D008665:Metalloporphyrins / Q000737:chemistry*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D014867:Water / Q000737:chemistry*
chemical_list: D050091:Dendrimers; D037741:Fullerenes; D008665:Metalloporphyrins; D014867:Water