Temperature-resolved study of the structural behaviour of nickel octahexyl phthalocyanine up to the liquid crystal transition

This paper describes a temperature-resolved crystallographic investigation into the behaviour of the title compound as the temperature is increased stepwise from room temperature up to 418 K, which is the temperature at which a transition to a discotic columnar mesophase takes place. The experiments were conducted using synchrotron radiation on Station 9.8 at the SRS at the Daresbury Laboratory. An intermediate transition to a less well ordered crystal form was seen at 326 K and differential scanning calorimetry (DSC) measurements confirmed the transition temperature of this change. Also, a new improved room-temperature crystal structure was obtained, as well as further structure determinations at 323, 328 and 353 K. These showed that as the mobility, particularly of the hexyl groups, increases with temperature, the packing of the molecules adjusts from pseudohexagonal layers to a rectangular arrangement.