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

Abstract

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.

Polymorph prediction of organic pigments

“…XRPD patterns obtained using standard laboratory based diffractometers are sufficient, even for very fine powders. The resulting structure is perfectly suitable as a starting model for the Rietveld refinement and for any calculation involving force fields for which the crystal structure is essential like morphology prediction [27]. …”

A design aid for crystal growth engineering

“…Bioavailability is central to pharmaceutical efficacy and can be impacted by the crystal shape [4][5][6]. Additionally, highaspect-ratio, needle-shaped crystals are typically undesirable for pharmaceutical applications, where the shape impacts downstream processing such as filtration [7][8], but can be preferred for the active layer morphology to enhance performance in electronic applications [9][10]. Figure 1.1 demonstrates a variety of crystal habits for pharmaceutical crystals; their faceted nature is evident with well-defined crystallographic planes.…”

Investigation into solid and solution properties of quinizarin

“…13). 36 The importance of the crystallization driving force in controlling needle growth in the gas phase for flat molecule stacked systems has also been demonstrated. The planes defined by the ribbons are 3.35 Å apart with the atoms of adjacent ribbons in van der Waals contact and this is typical of slipped π-stacked systems and similar to the packing in β-phthalocyanine and benzoic acid.…”