Abstract

The self-organizing capability of a family of newly synthesized ‘free-base', H₂(OASPz), and metal porphyrazines, M(OASPz) (OASPz²⁻ = 2,3,7,8,12,13,17,18-octakis(alkenylthio)-5,10,15,20-tetraazaporphyrinato dianion, n = 4, 5, 6, 8; M = Co, Ni, Cu), into columnar, discotic liquid crystals, has been investigated by differential scanning calorimetry (DSC), optical microscopy and X-ray diffraction. It is found that of the metal-free porphyrazines only those with n = 4 or 5 show, as indicated by X-ray and optical microscopy studies, characteristic stable and discotic nematic mesophases. All the metallated porphyrazines show a discotic liquid crystalline behavior and those with the largest values of n present, consistent with the X-ray results, hexagonal columnar packing. Comparing the mesomorphic behavior of these compounds with those of the parent compounds peripherally substituted with saturated alkyl(sulfanyl)-chains it is seen that the effect of the increased stiffness at the periphery of the chains, induced in the title tetrapyrroles by the terminal double bonds, results in a decrease of the clearing temperature, T_i, and also of the mesophase temperature stability range, ΔT. This effect is larger in H₂ and Ni than in Cu and especially in Co porphyrazines, where the axial coordinating capability of the Co seems to counterbalance the effect of this perturbation.