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Dendritic Metalloporphyrin–Fullerene Conjugates: Changing the Microenvironment around Redox‐Active Centers and its Impact on Charge‐Transfer Reactions
Author(s) -
Krokos Evangelos,
Spänig Fabian,
Ruppert Michaela,
Hirsch Andreas,
Guldi Dirk M.
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201202110
Subject(s) - redox , fullerene , conjugate , charge (physics) , chemistry , photochemistry , combinatorial chemistry , organic chemistry , physics , mathematical analysis , mathematics , quantum mechanics
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.