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Testing Electron Transfer within Molecular Associates Built around Anionic C 60 and C 70 Dendrofullerenes and a Cationic Zinc Porphyrin
Author(s) -
Sarova Ginka H.,
Hartnagel Uwe,
Balbinot Domenico,
Sali Sevda,
Jux Norbert,
Hirsch Andreas,
Guldi Dirk M.
Publication year - 2008
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.200701462
Subject(s) - chemistry , electron transfer , excited state , photochemistry , quenching (fluorescence) , microsecond , porphyrin , aqueous solution , photoinduced electron transfer , cationic polymerization , ultrafast laser spectroscopy , fluorescence , atomic physics , polymer chemistry , spectroscopy , physics , quantum mechanics , astronomy
Mono‐ and bis‐functionalized C 60 and C 70 fullerene derivatives ( DF , 1 – 10 ) that carry one or two oligoanionic dendritic termini in their malonate addends and an oligocationic octapyridinium zinc porphyrin salt ( ZnP ) were found to self‐assemble in buffered aqueous solution to yield a novel series of 1:1 and/or 1:2 electron transfer hybrid associates. Remarkably high association constants—typically on the order of 10 8 M −1 —were derived that corroborate stable complex formations. A combination of electrostatic and charge‐transfer interactions that are operative between the electron‐accepting DF and the electron‐donating ZnP is considered to contribute to the uniquely high complex stability. First insight into intracomplex excited state interactions came from steady‐state and time‐resolved fluorescence quenching experiments that were performed with the molecular ZnP / DF hybrid associates. Excited state quenching processes are, for example, evident in form of a bi‐exponential fluorescence decay of ZnP —corresponding to a distribution of associated and non‐associated ZnP . Unambiguous evidence for an intracomplex electron transfer quenching, namely, formation of ZnP .+ /C 60 .− and ZnP .+ /C 70 .− radical ion pairs, was gathered in time‐resolved transient absorption measurements. Lifetimes of these radical ion‐pairs range from nanoseconds to a few microseconds.