Luminescence properties and kinetic analysis of singlet oxygen from fullerene solutions

A systematic investigation on singlet oxygen (O2(a1Δ)) photoluminescence (PL) from fullerene (C60) solutions by using a pulsed Nd: YAG laser at 532 nm was reported. The results show that the O2(a1Δ) PL intensity first increases linearly, then declines fast, and eventually tends to level off with the increase of pump energy, while decreases monotonically with increasing irradiation time. The latter can evidently be attributed to the formation of photoinduced O2(a1Δ) quenchers, which was directly confirmed by the remarkable decrease of O2(a1Δ) lifetime with increasing irradiation time. Also, we further demonstrated that the O2(a1Δ) quencher should be C60O via electrospray ionization-mass spectrometry (ESI-MS) and a kinetic analysis on the formation rate of the O2(a1Δ) quenchers in irradiated C60 solutions. On this basis, the above pump-energy dependence of O2(a1Δ) PL was also rationalized kinetically. With the increase of pump energy, the initial linear increase is exactly attributable to the linear increase of O2(a1Δ) concentration, while the following drop should result from the fast formation of photoinduced O2(a1Δ) quenchers and the eventual smooth variation is evidently related to the inverse saturated absorption effect of C60.