Dynamics of second harmonic generation at the C60/quartz interface

The dynamics of electronic excited states is studied for thin C60 films on quartz by second harmonic generation. Time resolved measurements show that for films thicker than 100 nm a single excited state is observed, which is occupied in faster than 45 ps and decays over 20 ns or longer. Spectroscopic studies reveal that the state can be excited over the entire visible range following the C60 absorbance down to 1.6 eV. this indicates that excitonic states below the band gap, most likely the lowest singlet and triplet states, determine the suppression mechanism. For thin films below 100 nm thickness a second excited state with a substantially reduced lifetime of 70 ps is observed. This state is attributed to the C60/substrate interface and gives access to the coupling between C60 excitonic states and the immediate environment of the molecule.