Self-assembly and liquid-crystalline properties of 5-fluoroalkylporphyrins.
We report three crystal structures of a synthetic 5-fluoroalkylporphyrin molecule that was programmed for self-assembly. All the X-ray structures of zincated and free-base porphyrins Zn2 b, Zn5 a, and 2 b revealed rigorous pi-pi stacking and extremely hydrophobic interactions. Other the other hand, the strong aggregation of 5-fluoroalkylporphyrins in solution was also found. Interestingly, the regular nanopore formation of the 5-fluoroalkylporphyrin was visualized by atomic force microscopy (AFM). Importantly, the 5-fluoroalkylporphyrins possess liquid-crystalline properties that were confirmed by using a combination of differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) techniques. By comparison, the self-assembly of non-fluorine-containing porphyrins with similar structure showed much lower aggregation ability, as investigated by NMR techniques. Additionally, no birefringent mesophase was observed for the non-fluorine-containing porphyrin.