Synthesis And Propetries Of Novel Discotic Liquid Crystal Porphyrins And Their Metal Complexes

Porphyrin is a class of annular compound with highly conjugate system. Its fournitrogen atoms may coordinate with metal ions to generate correspondingmetalloporphyrin. Porphyrins and metalloporphyrins have an extensive system ofdelocalized π electrons and unique physical and chemical properties. Recently, theyhave shown a very broad application prospect for using in photodynamic therapy,solar cells, chemical sensors, gas sensor, optoelectronic devices, etc.Porphyrin liquid crystal is a function of the discotic liquid crystal. In1980,Goodby et al. synthesized the first simple liquid crystal porphyrin compound.Followed by that, a lot of new type liquid crystal porphyrin compounds have beensynthesized. Porphyrin liquid crystal can be used as organic photoconductor andsemiconductor materials.The photoelectric properties research of liquid crystalporphyrin have attracted scientists' attention. According to literature reports,synthesized liquid crystal porphyrins have problems of higher phase transitiontemperatures with bad stability of mesophase and narrower mesophase range, thus thedevelopment of liquid crystal porphyrin materials was restricted. However, the activesite of the porphyrin peripheral could link up different structures soft side chains. Andthen by molecular design, we could synthesize liquid crystal porphyrin with highstability of mesophase. Liquid crystal of porphyrin with amide group by using theintermolecular π-π interactions and intermolecular hydrogen bonds is expected to bewith better stability of mesophase at room temperature. In this paper, we synthesized aseries of novel benzoylamino-substituted porphyrins ligands bearing eight alkoxychains and their metal complexes. We also studied their liquid crystal properties.In this thesis, we synthesized a series of alkoxy phenyl chloride using theWilliamson reaction with molecular design, and then reacted with TAPP. We havesynthesized five benzoylamino-substituted porphyrins bearingdifferent chain length.At the same time, we have synthesized thirty-two transition metal and rare metalcomplexes. The molecular structure of the product has been characterized byelemental analysis, FTIR,1HNMR spectra and UV-Vis sectra. At the same time, wehave studied the products by fluorescence spectra, Raman spectra, cyclic voltammetry and thermal studies. These studies will provide an important foundation for thedevelopment and application of the materials. The main work that we have doneincludes the following aspects:1. Five novel5,10,15,20-tetra[4-(3,5-dialkoxybenzamide)phenyl]porphyrin ligandswere synthesized. The molecular structure of the product was confirmed byelemental analysis, FTIR,1HNMR and UV-Vis.Scheme1. The synthesis of porphyrin ligands2. We have used benzoylamino-substituted porphyrin ligands as raw materials byAlder method to synthesis Mn, Co, Cu, Zn complexes. The transition-metalcomplexes were characterized, and analyzed by means of elemental analysis, FTIR,1HNMR and UV-Vis. And so the molecular structure of the complexes was confirmed.Scheme2. The synthesis of transition metal porphyrin complexes3. Compared with transition metal, rare earth metal has unique electronic structure.Therefore, rare earth porphyrin complexes have attractive applications in manyfields. We have used two benzoylamino-substituted porphyrin ligands as rawmaterials to synthesis twelve Dy, Er, Eu, Gd, Sm, Yb rare metal porphyrincomplexes. The rare-metal complexes have been characterized by means ofelemental analysis, FTIR and UV-Vis.Scheme3. The synthesis of rare earth metal porphyrin complexes4. We have studied the photochemical properties, photophysical properties, redoxproperties and thermal properties of the five porphyrin ligands and their metal complexes. We also investigated the effects of chain length on their properties.(1) Fluorescence emission spectra: For transition metal complexes, only zincporphyrin complexes have strong fluorescence. And other transition metalcomplexes are much weaker. Some of these complexes even produce fluorescencequenching. For rare earth metal complexes, the Eu, Gd, Sm complexes havestrong fluorescence intensities. While the complexes of other three rare earthmetal produce fluorescence quenching. Whether transition metal or rare earthmetal complexes, the central metal ion have relatively large effect on thefluorescence intensity. For porphyrin ligands with alkoxy chain and theircomplexes, their fluorescence quantum yield changed irregularly. This shows thatthe chain length has little effect on the fluorescence properties.(2) Raman spectra: In porphyrin ligands, the band about1553cm-1of is assigned toCβ Cβstretch ν2.In Zn complexes, it is down shifted. And in Mn complexes, it isup shifted. The band around1350cm-1is another important structure sensitiveband of porphyrin ligands, which is assigned to the ν(Cα-N)/ν(CαCβ) stretchν4.And it is red shifted to1369cm-1in Mn complexes and bule shifted to1353cm-1in Zn complexes, and that is because of the influence of metal ions. The bandat about400cm-1of metal complexes are assigned to M-N stretching vibration.InMn complexes, the band at about363cm-1is assigned to vibration of M-Cl.Moreover, the chain length of porphyrin compounds has little effect on Ramanspectra.(3) Thermal studies: Porphyrin ligands and their metal complexes have good thermalstability.In the air, they will not change for heating and drying in the conditionsbelow200oC. And the decomposition of the benzoylamino-substituted porphyrincompounds is a continuous process.They first loss of side chanins when heat to acertain temperature.At last, porphyrin skeleton is decomposed.(4) Electrochemical properties: The voltammograms of porphyrin ligands, Cu andZncomplexes are similar, which correspond to redox reaction of porphyrin ring.However, Mn and Co complexes not only have the redox of the porphyrin ring,but they also have the redox of the cental metal ion. The chain length of thecompounds has little influence on redox potential. This shows that theirsubstituent effect of the side chain is basically the same. In addition, the complexes are more easily reduced than the porphyrin ligands.5. The liquid crystal behaviors of benzoylamino-substituted porphyrin ligands andtheir metal complexes were researched by means of DSC, POM and XRD. Theresults show, only the side chain with above12carbon atoms, the porphyrinligands and their Zn complexes show liquid crystal properties. Their mesophaseexhibit low phase transition with good stability and wide temperature range.