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

Graphical Metalloporphyrin liquid crystals : Well-organized hexagonal columnar mesophases of broad temperature ranges have been achieved in metal complexes of easily available fatty acid octaester substituted porphyrins. The liquid crystallinity of the free base and the metal porphyrins can be tuned with variant length side-chain substituents and different coordinated metal ions (see figure; TPP=tetraphenyl porphyrin). A series of meta -substituted fatty acid octaester derivatives and their transition-metal complexes of meso - tetraphenyl porphyrins (TPP-8OOCR, with R=C n −1 H 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