Thin solid films of C 6 0 and C 7 0 have been found to be sensitive to UV-visible light. In the absence of oxygen, which acts as a triplet state quencher, C 6 0 and C 7 0 have been observed to phototransform from a toluene-soluble to a toluene-insoluble state. This phototransformation has been studied via Raman and FTIR spectroscopies, UV-visible transmission spectroscopy and laser desorption mass spectroscopy. The results of these experiments have been interpreted as evidence for a phototransformation from a van der Waals solid to one in which the fullerenes are linked by covalent bonds. For C 6 0 , it is proposed that a transformation to a polymeric solid has occurred, whereas a similar flux of UV-visible light applied to C 7 0 is proposed to lead to a random dimerization of the lattice and a much smaller population of higher oligomers. For both phototransformed C 6 0 and C 7 0 , the covalent bonds between fullerenes can be broken thermally and the phototransformed material returns to the pristine, toluene-soluble state. UV-visible light can also be used to photochemically assist the diffusion of dioxygen into the interstitial voids in the solid C 6 0 and C 7 0 lattices. For C 6 0 , a photochemical enhancement of the O 2 diffusion rate by a factor of ~ 10 is observed by alpha particle backscattering, leading to a stoichiometry of ~ C 6 0 O 2 . Similar to C 6 0 -polyfullerene, C 6 0 (O 2 ) x is also toluene insoluble. As a result, these C 6 0 -based films might find photolithographic applications.