Details of the decay of the spot diffraction patterns from molecular crystals of copper phthalocyanine and some chlorinated derivatives have been studied as a function of radiation dose. To facilitate recording and storage of these electron intensities, a digital scanning diffractometer was constructed and is described briefly. Copper phthalocyanine is shown to have a radiation sensitivity typical of aromatic compounds, although some long range order persists for doses ≈1 to 2 C cm −2. The chlorinated derivatives have apparently a much greater stability, and an explanation of this and the dependence on the degree of chlorination is given. It is shown that molecular damage probabilities in chlorinated copper phthalocyanine depend on the molecular environment and crystal shape.