DYNAMICS OF 2ND-HARMONIC GENERATION AT THE C-60 QUARTZ INTERFACE/

The dynamics of electronic excited states is studied for thin C-60 fil ms on quartz by second harmonic generation. Time resolved measurements show that for films thicker than 100 nm a single excited state is obs erved, which is occupied in faster than 45 ps and decays over 20 ns or longer. Spectroscopic studies reveal that the state can be excited ov er the entire visible range following the C-60 absorbance down to 1.6 eV. This indicates that excitonic states below the band gap, most like ly the lowest singlet and triplet states, determine the suppression me chanism. 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 C-60/substrate interface and gives access to the coupling between C-60 excitonic states and the immediate environment of the molecule.