Structure and magnetic alignment of metalloporphyrazine columnar aggregates in their mesophases and crystalline phases

Abstract

The response of a series of metalloporphyrazine liquid crystals to external magnetic fields has been investigated. Small-angle neutron scattering (SANS) data of the octa(n-decylthio)-porphyrazine complexes of the diamagnetic late first-row transition elements (Ni, Zn) reveal a perpendicular orientation of the columnar directors with respect to applied magnetic fields as low as 0.50 T when the samples are cooled from their isotropic phases. The threshold aligning field for the analogous cobalt derivative is half that of the diamagnetic complexes, while the copper porphyrazine exhibits no preferred alignment at fields as high as 1.02 T. We account for these observations on the basis of the competing diamagnetic and paramagnetic moments of the complexes. Correlated solid state and mesophase C-13 NMR studies on the nickel and zinc complexes indicate time-averaged disk tilt angles of 27degrees with respect to the columnar directors in the liquid-crystalline phase.