We have studied thin films of C 60 , [6,6]-phenyl-C61-butyric acid methyl ester, and fullerenol by Near-Edge X-ray Absorption Fine Structure Spectroscopy at the C1s edge. The advantage of this technique is the sensitivity to unoccupied π states within the sp 2 chemical bond structure. In particular, we focus on the relative intensity of the C1s→π*(p-p) transitions. Upon adding functional groups to the C 60 molecular frame, the intensity of these bands is reduced or almost vanished accompanied by increasing C1s→π*(s-p) transitions. This finding is confirmed by Xray photoemission data in the valence band region where the peaks according to the occupied π states disappeared particularly in the fullerenol films. These data in combination with the quantitative analysis of the C1s core level data suggest that C=C double bonds are broken when binding two OH-groups correlated to a change of the carbon bonding state from sp 2 to sp 3 .