Testing electron transfer within molecular associates built around anionic C60 and C70 dendrofullerenes and a cationic zinc porphyrin |
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Authors: | Sarova Ginka H Hartnagel Uwe Balbinot Domenico Sali Sevda Jux Norbert Hirsch Andreas Guldi Dirk M |
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Institution: | Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials, University of Erlangen-Nuremberg, Egerlandstrasse 3, 91058 Erlangen, Germany. |
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Abstract: | 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. |
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Keywords: | electron transfer fullerenes porphyrinoids time‐ resolved transient‐absorption spectroscopy |
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