A STUDY OF THERMALLY ACTIVATED DELAYED FLUORESCENCE IN C-60

The existence of thermally activated delayed fluorescence in C-60 is d emonstrated by the study of the temperature dependence (291-353 K) of the fluorescence intensity of C-60 degassed solutions. The determined singlet-triplet energy gap, 35 +/- 2 kJ/mol, agrees with the value cal culated from previously reported fluorescence and low temperature phos phorescence spectra for this molecule (35 kJ/mol). The estimated quant um yield of triplet formation, 0.8 +/- 0.1, agrees with previous deter minations. The fluorescence lifetime of C-60, also measured, tau = 1.1 ns, does not change appreciably with excitation wavelength, degassing nor with temperature, in the range 243-343 K. (C) 1997 Elsevier Scien ce B.V.