Time-resolved thermally activated delayed fluorescence in C-70 and 1,2-C70H2

Thermally activated delayed fluorescence (TDF) emission from C-70 and 1,2-C 70H2 has been time-resolved to provide thermodynamic and kinetic informatio n on excited electronic states. The energy gap between S-1 and T-1 states w as deduced from the temperature dependence of initial TDF intensities and i ndependently from the ratio of TDF intensity to time-integrated prompt fluo rescence. S-1-T-1 gaps were found to be approximately 2470 cm(-1) for C-70 and 2180 cm(-1) for 1,2-C70H2, with relative uncertainties of 2-3%. Time-re solved TDF measurements from fullerene samples immobilized in PMMA films re vealed lifetimes for triplet state decay unaffected by bimolecular deactiva tion processes. The intrinsic triplet lifetimes at 298 K were found from bo th TDF and transient absorption measurements to be 24.5 +/- 1.5 ms for C-70 and 1.95 +/- 0.1 ms for 1,2-C70H2.