Mesophase behaviour and thermal stability of octa-alkoxy substituted phthalocyaninatocobalt(II) complexes

Abstract

Cobalt(II) phthalocyanines substituted with eight alkoxy chains in the peripheral (2, 3, 9, 10, 16, 17, 23, 24) positions were prepared. The alkoxy chain length was varied between n-butyloxy (C4H9O) and n-octadecyloxy (C18H37O). Studies by polarizing optical microscopy and high temperature X-ray diffraction revealed that all the complexes are liquid crystalline and that they exhibit a hexagonal columnar mesophase (Col(h)). Transition enthalpies were determined by differential scanning calorimetry. The clearing point could only be observed for compounds with a chain length longer than C13H27O. Both the melting and clearing points decrease with increasing chain length. The transition temperatures of these discotic metallo-mesogens are higher than those of the corresponding metal-free phthalocyanines, but are comparable with those of the corresponding copper(II) compounds. The thermal decomposition of the compounds was studied by thermogravimetry.