PHOTOPHYSICAL PROPERTIES OF FULLERENES AND FULLERENE/N,N-DIETHYLANILINE CHARGE-TRANSFER COMPLEXES

Well-resolved fluorescence and phosphorescence spectra of fullerenes in methylcyclohexane and the determination of important photophysical parameters are reported. The fluorescence quantum yield depends on the excitation wavelength, which indicates the occurrence of a very rapid photoprocess directly from upper excited states, in competition with internal conversion to the lowest excited state. For C70 the fluorescence quantum yields are 6 x 10(-5) at 370 nm, 1.3 x 10(-4) at 378 nm, and 2.2 x 10(-4) at 471 nm. The singlet-triplet energy splitting for C70 is 7.0 kcal/mol. For C60 the fluorescence quantum yields are 1.9 x 10(-5) at 405 nm and 3.8 x 10(-6) at 370 nm. The singlet-triplet energy splitting for C60 is 5.5 kcal/mol. In the presence of N,N-diethylaniline (DEA), charge-transfer complexes between fullerenes and DEA for formed. In the excited state, luminescence from both the singlet and the triplet exciplex of C70 are observed.