Broad Hexagonal Columnar Mesophases Formation in Bioinspired Transition-Metal Complexes of Simple Fatty Acid meta-Octaester Derivatives of meso-Tetraphenyl Porphyrins.

A series of meta-substituted fatty acid octaester derivatives and their transition-metal complexes of meso- tetraphenyl porphyrins (TPP-8OOCR, with R=C _n−1H_{2 n−1}, n=8, 12, or 16) have been prepared through very simple synthesis protocols. The thermotropic phase behavior and the liquid crystalline (LC) organization structures of the synthesized porphyrin derivatives were systematically investigated by a combination of differential scanning calorimetry (DSC), polarized optical microscopy (POM), and variable-temperature small-angle X-ray scattering/wide-angle X-ray scattering (SAXS/WAXS) techniques. The shorter octanoic acid ester substituted porphyrin (C8-TPP) did not show liquid crystallinity and its metal porphyrins exhibited an uncommon columnar mesophase. The lauric acid octaester (C12-TPP) and the palmitic acid octaester (C16-TPP) series porphyrins generated hexagonal columnar mesophase Col_h. Moreover, the metal porphyrins C12-TPPM and C16-TPPM with M=Zn, Cu, or Ni, exhibited well-organized Col_h mesophases of broad LC temperature ranges increasing in the order of TPPNi<TPPCu≤TPPZn with their increased effective ionic radii in the square-planar coordination. The simplicity in synthesis, the well intercolumnar organization of Col_h mesophase, the broadness of the discotic LC range, and the specific UV/Vis absorption and fluorescence emission behaviors make the symmetrically substituted fatty acid octaester porphyrins and their metal complexes very attractive for variant applications. [ABSTRACT FROM AUTHOR]