Abstract In order to elucidate the effect of the crystal structure on the chemical behavior of 64Cu recoil atoms in copper phthalocyanine, the author studied the mixed system of copper and metal-free phthalocyanine. It was found that the initial retention increased both in the mixed crystal and in the mixed-disk target. The addition of metalfree phthalocyanine sensitized the target to the thermal annealing reaction, and the rate of the reaction in the mixed crystal was faster than that in the unmixed crystal. The electron acceptor in the target was also found to increase the initial retention. The results were discussed in terms of the electrical properties of the target, which were changed by the change in the spatial arrangement of the molecules.