In order to elucidate reaction mechanisms of free radical photo-sensitive materials, flash photolytic investigations are made on the following systems; diphenylamine, N-phenyl-l-naphthylamine-tetrabromomethane, tribromomethane, dibromomethane, 1, 2-dibromoethane, benzylbromide, tetrachloromethane, trichloromethane. On all systems, the absorption spectra and decay of the amine cation radicals are observed. Also on diphenylamine-tetrachloromethane and trichloromethane systems, it is observed that the N type radical of diphenylamine is made from diphenylamine cation radical quantitatively. According to these results, it is confirmed that the common photochemical process via exciplex formation, charge separation, dissociation to amine cation radical and anion radical of corresponding halogenated compound takes place on every system. Also it is confirmed that the first nonionic intermediates of dye forming reactions are the aromatic amine N type radical and the radical A · of halogenated compound AX. Moreover the refined and more elaborate reaction mechanisms are presented.