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Editor: Greta Heydenrych; Editorial Board Chairs: Christian Amatore, Michael Grätzel, Michel Orrit
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Online ISSN: 1439-7641
Cover Picture: The Brightest Fullerene: A New Isotope Effect in Molecular Fluorescence and Phosphorescence (ChemPhysChem 7/2011)
The cover picture shows the effect of 13C on the excited-state kinetics of the fullerene C70, described on p. 1247 by C. Baleizão and M. N. Berberan-Santos. Substitution of 12C by 13C in C70 leads to major changes in its delayed fluorescence and phosphorescence properties. Delayed fluorescence lifetime (τDF) as a function of delayed fluorescence intensity (IDF/IPF) is shown in the graph for 12C70 (squares) and 13C70 (stars) in polystyrene, and from the linear fit to the experimental points it is possible to obtain the quantum yield of triplet formation: 0.994 for 13C70 and 0.990 for 12C70. The hitherto unknown effect of 13C on molecular luminescence, also observed for C60, decreases the internal conversion and T1So intersystem crossing rates by a mass effect, and increases the S1T1 back intersystem crossing rate by a nuclear magnetic effect. A small increase (0.4%) in the quantum yield of triplet formation leads to the doubling of the high-temperature fluorescence quantum yield. As a consequence, 13C70 is by far the brightest fullerene known, attaining a maximum fluorescence quantum yield of 9%. This upper value (equation depicted on the right) results from a large number of excited-state cycles of the type S1T1S1 (as many as 170, on average) that increase the probability of decay through fluorescence. The strong delayed fluorescence intensities and long delayed fluorescence lifetimes of 13C70 render this isotopologue a serious candidate for optical oxygen sensors with unprecedented detection limits at the ppbv level.