The strategy of rendering an unreactive molecular solid reactive by doping is illustrated for the case of phthalonitrile doped with diiminoiso-indoline. The doped solid undergoes thermal reaction, and the product of the reaction is identified as phthalocyanine by solution spectrophotometry. The possible crystal chemistry associated with this new reaction is discussed. X-ray powder diffraction of phthalonitrile and its doped phases indicates the presence of multiple crystalline phases. The solid state decomposition of phenyliminoisoindoline has been studied, and some of the reaction products were identified.