Higher fullerenes such as C 84 present a rich variety of photophysical properties, due to their abundance of distinct geometric isomers. However, this multitude of isomers, along with their similar chromatographic properties, also creates difficulties in purifying and characterizing specific species of C 84 . In this paper, we present the application of an alternating-column HPLC technique to resolve C 84 isomers. We find that this technique presents markedly higher separation efficiency than the recycling HPLC method. Subsequent photophysical analysis of a previously uncharacterized isomer of C 84 , D 2d (I), shows its transient absorbance properties clearly differ from those of other C 84 isomers, in terms of both its spectral features (with maxima at 620 and 840 nm) and lifetime (ca. 45.6 μs). Singlet-oxygen quenching experiments demonstrate that the T 1 energy of D 2d (I) lies below 7880 cm -1 . Finally, the ground-state absorptivity of the D 2d (I) isomer has been characterized via quenching experiments with palladium octaethylporphyrin, showing an ε = 21,400 M -1 cm -1 at a local maximum of 590 nm.

Photophysical properties Of C-84 isomers have been measured separately and compared. Intrinsic triplet state lifetimes at room temperature are found to differ dramatically: 4.5 us for the D-2d(II) isomer, 125 mu s for C-s(a), and 640 mu s for D-2(IV). The triplet lifetime of D-2(IV) C-84 represents the second longest found to date among fullerenes. Measurements between 77 and 320 K reveal that the triplet decay kinetics of D-2d(II) is largely temperature-independent, whereas thermally activated channels dominate triplet decay in the D-2(IV) isomer. Oxygen-quenching studies suggest that the T, energy of D-2d(II) lies near 7600 cm(-1) but that of D-2(IV) exceeds 8000 cm(-1). These results highlight the importance of isomeric separation in exploring the rich photophysics of higher fullerenes.