Synthesis, Mesomorphic Behavior And Catalytic Polymerization Studies Of Porphyrin Derivatives

The recent advances in the field of porphyrin derivatives were summarized in the thesis. Porphyrin is a big conjugate annular compound with four nitrogen atoms which may coordinate with metal ions. Porphyrin derivatives have received considerable attention and attracted significant interest for their particular structure and unique physical and chemical properties. They have played an important roll in the field of biological chemistry, medical chemistry, analytical chemistry, catalytic chemistry, material chemistry, etc. Porphyrin derivatives have received considerable attention and attracted significant interest. The review showed the promising applications and the fundamental research trend, especially showed the progress in liquid crystals and catalytic polymerization.Since the first liquid crystalline porphyrin which shows mesomorphic behavior was synthesized by Goodby in 1980, liquid crystal porphyrins have received considerable attention for their unique photoeletronic property. Synthesized liquid crystal porphyrins have problems of bad stability of mesophase with higher phase transition temperatures and narrower mesophase range. As a result, the application of liquid crystalline porphyrin was restricted. Worthwhile, the periphery of porphyrin and its metal complexes has 12 active positions, which could link up different structures soft side chains. So, we would synthesize new type liquid crystal of porphyrin materials with better stability of mesophase by molecular design. Besides, metalloporphyrin as catalyst for polymerization of epoxides, cyclic carbonate, methacrylonitrile, etc. has been researched widely, but few metalloporphyrin for olefin polymerization has been reported yet. A. Sen reported metalloporphyrin catalyst for olefin polymerization in 2001, and then opened a new area of porphyrin catalyst.In this thesis, two series of porphyrin derivatives and their metal complexes were synthesized. The proposed molecular structure of the compounds has been confirmed with 1H NMR, elemental analysis, etc. Their mesomorphic behaviors have been researched by DSC, polarized microscopic observation (POM), and X-ray diffraction. Combined with molecular simulation and density studies, the structures of their mesophase were proposed. Besides, the electron transfer between mesomorphic porphyrin and CNTs upon non-covalent method using UV-Vis and fluorescent spectra was studied. Finally, the catalytic property of metal porphyrin was studied. Nickel tetraphenylporphyrin (Ni(II)TPP) was synthesized, and was used in catalytic styrene polymerization using MAO as cocatalyst. The mechanism of the polymerization was discussed and a special coordination mechanism was proposed.I. The synthesis and characterization of porphyrin derivativesIn this section, two types of liquid crystal porphyrins derivatives, benzoate-substituted porphyrins and benzoylamino-substituted porphyrins, and their metal complexes were synthesized. The proposed molecular structure was confirmed with elemental analyses, UV-Vis, FTIR, and 1H NMR. The two series of novel liquid crystalline porphyrins were summarized below:(1) Benzoate-substituted porphyrin: meso-tetra[4-(3,4,5-tri-n- alkoxy- benzoate)phenyl]porphyrins (n=7, 12, 16), and its nickel and zinc complexes (n=12);(2) Benzoylamino-substituted porphyrin: meso-tetra[4-(3,4,5-n-trialkoxy benzoyl amino)phenyl]porphyrins (n=12, 16), and its nickel and zinc complexes (n=12). II. The mesomorphic behaviors of porphyrin derivativesThe mesomorphic behaviors of porphyrin derivatives were researched by DSC, POM, and XRD. Combined with molecular simulation and density studies, their phase structure and molecular packing model was proposed.All the two series of porphyrin derivatives showed their mesophase under certain temperature and the molecules can self assembled in their mesophase with good stability including wide temperature range and low phase transition temperature. All of the porphyrin derivatives exhibited rectangular columnar phase. Their mesomophic behaviors were greatly dependent on the length of the alkyl chains and their central metal atom. The phase transition temperatures of crystal phase to liquid crystalline (LC) phase(Tm) and LC phase to isotropic phase (Tc) were summarized below: OMR12, Tm=-33 oC, Tc=146.5 oC; AMR12, Tm=-26.0 oC, Tc=225.7 oC; OMR16, Tm=17.5 oC; Tc=109.5 oC; AMR16, Tm=19.3 oC, Tc=189.3 oC; OMR12Zn, Tm=-28.5 oC, Tc=116 oC; AMR12Zn, Tm=-29.9 oC, Tc=203.1 oC; OMR12Ni, Tm=8.6 oC, Tc=136.7; AMR12Ni, Tm=-28.2 oC, Tc=214.3 oC; OMR7, Tm<-50 oC, Tc=169.1 oC.The Tm of benzoylamino-substituted porphyrin is similar to that of benzoate-substituted porphyrin with the same chain length, but its Tc is rather higher than that of benzoate-substituted porphyrin. Temperature resolved FTIR spectra studies of AMR12 revealed that hydrogen bonding interaction could influence its molecular assemble in its mesomorphic phase, which lead to a more stable mesophase. Finally, liquid crystalline nano-congeries was prepared using precipitation method.III. Electron transfer behavior of porphyrin/carbon nanotubes systemElectron transfer behavior between mesomorphic porphyrin and carbon nanotubes (CNTs) was studied using UV-Vis and fluorescence spectra, which showed that supramolecular system formed and electron transfer occurred from porphyrin to CNTs, forming electron Donor-Acceptor system, in all conditions including neutral, acid and base solution.We also developed a simple method to improve nanotube solubility using covalent method. The modified nanotubes displayed good solubility in chloroform, and the electron transfer between porphyrin and modified CNTs was also studied, which revealed they maybe used as energy or electron transfer antennae.IV. Styrene polymerization catalyzed by Ni(II)TPP/MAO for synthesizing polystyreneIn this section, nickel(II) tetraphenylporphyrin (Ni(II)TPP) was synthesized, and the polymerization of styrene catalyzed with Ni(II)TPP/methylaluminoxane (MAO) was studied. Studies at different polymerization conditions showed that the catalyst system has a high thermal stability and show fairly good activity. The obtained polystyrene was isotactic-rich atactic polymer with narrow molecular weight distribution (PDI=1.5-1.6).A special coordination mechanism was proposed using ESR, 13C NMR, etc. With initiation, interaction of Ni(II)TPP and MAO formed the polymerization species, on which styrene monomer can insert through 2,1-fashion. More styrene molecules insert and propagating chains are formed. The propagating chains are terminated mainly throughβ-hydrogen elimination.