Unusual photoluminescence behavior of C₇₀

Well-resolved photoluminescence (PL) spectra of C₇₀ and ¹³C₇₀ in a glassy methylcyclohexane matrix have been obtained over the range 10 000-16 000 cm^-1 at temperatures between 4 and 77 K. The PL spectrum consists of a short-lived, red fluorescence system extending from 14000 to 15500 cm^-1 and a longer-lived, IR phosphorescence system extending from 10 000 to 12 500 cm^-1. The PL spectrum is unusual in several aspects: the line widths are nearly 10-fold narrower than those of catacondensed hydrocarbons under similar conditions, and the temperature dependence suggests the presence of multiple emitting states (of the same spin multiplicity) or several emitting species in the highly dilute glassy matrix. To better understand the photophysical behavior of C₇₀, we have attempted to correlate vibrational frequencies in the IR and Raman spectra of C₇₀ and ¹³C₇₀ with the vibronic intervals observed in the PL spectra. The study of ¹³C⁷⁰ enabled a more detailed analysis of the vibronic structure of the fluorescence and phosphorescence spectra.