UNUSUAL PHOTOLUMINESCENCE BEHAVIOR OF C-70

Well-resolved photoluminescence (PL) spectra of C-70 and C-13(70) in a glassy methylcyclohexane matrix have been obtained over the range 10000-16000 cm(-1) at temperatures between 4 and 77 K. The PL spectrum consists of a short-lived, red fluorescence system extending from 14 000 to 15 500 cm(-1) and a longer-lived, IR phosphorescence system extending from 10000 to 12500 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 C-70, we have attempted to correlate vibrational frequencies in the IR and Raman spectra of C-70 and C-13(70) with the vibronic intervals observed in the PL spectra. The study of C-13(70) enabled a more detailed analysis of the vibronic structure of the fluorescence and phosphorescence spectra.