A study of thermally activated delayed fluorescence in C60

The existence of thermally activated delayed fluorescence in C60 is demonstrated by the study of the temperature dependence (291–353 K) of the fluorescence intensity of C60 degassed solutions. The determined singlet-triplet energy gap, 35 ± 2 kJ/mol, agrees with the value calculated from previously reported fluorescence and low temperature phosphorescence spectra for this molecule (35 kJ/mol). The estimated quantum yield of triplet formation, 0.8 ± 0.1, agrees with previous determinations. The fluorescence lifetime of C60, also measured, τ = 1.1 ns, does not change appreciably with excitation wavelength, degassing nor with temperature, in the range 243–343 K.