Synthesis and Mesogenic Properties of Porphyrin Octaesters

A new and efficient method of preparing 3,4-pyrrolediacetic esters 3 is reported, together with their conversion, according to the Lindsey procedure, to a series of octa- and dodeca-substituted porphyrins. This procedure, which consists of a palladium-catalysed oxidative alkoxycarbonylation of N-substituted dipropargylamine derivatives 1, works nicely for n-alkyl alcohols in the range C1 to C14. The thermotropic behaviour of this series of porphyrins (28 compounds) has been investigated using polarization microscopy, DSC, X-ray diffraction, and miscibility tests. The planarity of the macrocyclic core constitutes the major structural requirement for mesophase formation. The mesophase temperature range is controlled by the length of the side chains through the melting point and by the strength of π-π interactions among the cores through the clearing point. The same set of rules governing porphyrin packing in the solid state can be employed to predict mesophase formation and organization in porphyrin octaesters