Research On Preparation, Structure & Characterization Of Meso-tetra-(p-acyloxyphenyl) Porphyrin Liquid Crystal

Metalloporphyrins have been extensively studied in many functional chemistry fields such as photosensisers, photoconductors, optical actuator and chemical sensors. A great deal of research is being devoted to the understanding of systems, biomimetic and otherwise, that self-assemble into organized structures. Liquid crystals represent one of the best known classes of self-organizing materials, exhibiting properties that range from surfactants that can form micelles, monolayers, and membranes, to the rodlike molecules used in liquid crystal displays, to the recently discovered disc-like liquid crystals. In all of the studies of mesogenic porphyrins, the extended disc-like core has been periphrrally substituted and therefore used as the basis for the construction of discotic materials. All of these compounds will form ordered but fluid structures, and more fluid phases tend to reorder themselves. In this communication, we reported on the synthesis of meso-tetra ( 4-decanoylphenyl ) porphyrin, meso-tetra ( 4-lauroyloxyphenyl ) porphyrin, meso-tetra (4-mystoyloxyphenyl) porphyrin, meso-tetra (4-palmitoyloxy phenyl) porphyrin and its derivatives.Meso-tetra (4-acyloxyphenyl) pophyrin was prepared by usual procedure from acyl chloride and meso-tetra ( 4-hydroxyphenyl ) porphyrin in benzene and obtained in 86.4% yield. Treatment of the free base with zinc chloride in dimethyl formamide (DMF)-dichloromethane(CH2Cl2) yielded corresponding zinc porphyrin complex. The spectral data (UV-visJR/H-NMR) and elemental analysis are in agreement with the assigned structures. The physical behaviors of TDPPH2, TLPPH2, TMPPH2, TPPPH2 and TDPPZn, TLPPZn, TMPPZn, TPPPZn by differential scanning calorimetric (DSC). The results show that four porphyrin free bases and its zinc porphyrins exhibit liquid crystal behaviors. On cooling from the isotropic liquid, TDPPH2, TLPPH2, TPPPH2 gave two broad LC phases separated by sharp peaks in the DSC. TMPPH2 gave a single, highly viscous, birefringent mesophase. The TMPPZn showed single liquid crystalline phase, TDPPZn and TLPPZnshowed two liquid crystalline phases, TPPPZn showed three liquid crystalline phases between the isotropic liquid and crystalline phase, and the phases were separated by sharp peak in the DSC. According to the DSC thermogram of compounds, the free base porphyrin (TPPPHi) has a low phase transformation temperature 14.36?, TMPPH/z has a high phase transformation temperature 52.04 ?. The zinc complex TLPPZn has a low phase transformation temperature - 36.40 ?, TPPPZn has a phase transformation temperature 15.84?. The free base porphyrin TPPPH2 has a narrow mesophase from 14.36? to 65.85? (51.49?) , TLPPH2 has a broad mesophase from 25.95 ? to 134.51? (108.56?) . The zinc complex TLPPZn has a narrow mesophase from -36.40? to 39.78? (76.18 ?), TDPPZn has a broad mesophase from -8.99? to 166.0? (175 ?).The electrochemical behaviors of the porphyrin free base and metal complexes were invesrigated by cyclic voltammorgrans and OTTLE.The effect of central metal was' investigated, the results showed that the central metal ( Zn ) has a dramatic effect on mesophase formation in the porphyrin complex, which was absent the corresponding free base.The thermotropic behavior of these compounds has been investigated as a function of length of the meso-side carbon chain. The results showed that a function of length of the side chain has a dramatic effect on mesophase formation in the porphyrin free base and complex.The optical textures of the porphyrin free bases and zinc complexes was observed by microscopy and resembles that of a columnar discotic phase.