The photochemical and photophysical properties of the three C-121 isomers (I, II, III) were investigated with MADLI-TOF-MS, UV-vis spectra, fluorescence spectra, absorption spectra of their DMA complexes, and theoretical calculations. The three isomers of C-121 (I, II, III) have different stabilities under laser irradiation, but isomer I and isomer II show good stability against the heat-induced conversion between different isomers: No conversion between the isomers was found after heating the mixture of isomer I and isomer II at 353 K for 12 h in Ar atmosphere. The results of UV-vis absorption and fluorescence spectra indicate that interactions between two C-60 moieties of C60CC60 in the ground and singlet states are not significant, C-121 (I, II, III) behaves as an electron-acceptor similar to C-60. These indicate that the formation of the fullerene chain structure (e.g., C60CC60) does not disturb the photochemical and photophysical properties of the C-60 monomer itself, even that the properties were enhanced by the formation of the polymer. This is significant for the C-60 polymer in photochemical or photoelectronic applications in which C60CC60 can be an excellent basic unit of polymers.