Study of the Needle-Like Morphologies of Two β-Phthalocyanines

The needle morphology of the commercial blue pigments copper phthalocyanine and metal-free phthalocyanine is studied using computer simulations and is compared with vapor grown crystals. Both phthalocyanines grow from the vapor at 700 K as very thin needles. The crystals are faceted along the needle axis, having one basal face and several side faces, and are not faceted at the top. The structures of the two phthalocyanines are similar and highly anisotropic leading to one preferred direction of growth. Conventional morphology methods fail to predict the correct morphology and aspect ratio of the needles. The morphology of the metal-free phthalocyanine crystals was simulated using the attachment energy method, kinetic Monte Carlo simulations, and a new morphology tool, STEPLIFT, based on a step energy approach. Kinetic Monte Carlo simulations give the most accurate representation of the experimental morphology, explaining also the variety of the observed side faces. STEPLIFT gives reasonable results in a much shorter time.