Study On Peripheral Modification Of Porphyrins Via Aromatic Nucleophilic Substitution Reactions(S_NAr)

Porphyrin is a kind of macrocyclic molecular with large conjugated aromatic structure. This kind of compounds and their derivatives have attracted numberous atterntion from researchers in the areas of materials, catalysis, medicine and analysis because of their inherently excellent photoelectron properties and catalytic activities, as well as bioactivities. The performances of porphyrin derivatives are strongly affected by peripherally substituted functional groups and many modification strategies are eagerly needed to get access to these new structures. Post-modification of porphyrin core proves to be one of the most efficient methods to achieve this goal. Thus, in recent years, peripheral modification of porphyrins has become an attractive research topic among chemists all over the world. Based on the previous research, the topics of this thesis are mainly focused on these aspects:1. We have reviewed recent research progress in porphyrin chemistry, including their structures and properties, preparation methods and practical applications. The functions of porphyrin derivatives are determined by their properties, which could be modulated by central coordination metal ions and substituent groups on the peripheral. Compared to the methods of central metallization, directly peripheral modification of porphyrine core possesses higher practical value, since numberous organic functional groups would provide a lot of new porphyrins to fufill people’s increasing demands for novel compounds. Our attention are focused on the most widely applied peripheral modification ways, which means β-position modification strategies, meso-position modification strategies, as well as functionalization of aromatic ring on porphyrin core.2. In this thesis, we have studied a facial method to achieve meso-position functionalization of porphyrin via aromatic nucleophilic substitution reaction (SNAr). meso-Substituted (O, S, C) porphyrins could be obtained in high yields by heating the solution of bromoporphyrin in DMF using soft nucleophiles as substrates, with Cs2CO3as addictives in the absence of transition metal catalysts. This reaction could be applied to a large range of substrates, such as phenol derivatives, aliphatic alcohols, thiophenol derivatives, thiols derivatives,1,3-dicarbonyl derivatives and carbon anions. The desired meso-substituted porphyrins could be obtained in high yield under the optimized conditions. In addition, we have also observed the reactivity was strongly affected by central coordinated metal ions, and meso-bromoporphyrin (M=2H) could be reacted with phenol, phenyl mercaptan as well as aliphatic thiol derivatives to form meso-substiuted-porphyrin. When Zinc (II) ions were inserted into the porphyrin core, the reactivity was strongly hindered most probably as a result of electronnegativity and coordination effect. While when nickel or coper ions were inserted, the reactivity was strongly accelerated as a result of decrease of electron density on the peripheral of porphyrin core.3. We have reported the synthesis of meso-fluoroporphyrin from easily available porphyrin synthons via SNAr reaction for the first time. meso-N02as well as halogen-substituted porphyrins (F, Cl, Br, I) could all be participated in this kind of transformation. The reactivities of different meso-substituted porphyrins reacting with phenols were measure and ranked in the order:F> Cl> NO2> Br> I. This characteristic is in consistence with typical addition-elimination mechanism of aromatic nucleophilic substitution reactions. Judging form these facts, we conclude this reaction most probably proceded through a typical addition-elimination mechanism or a Meisenheimer complex process.4. In this thesis,36new porphyrin monomers and3porphyrin dimers have been synthesized, whose structures were characterized by’HNMR,13C NMR as well as HR-MS unambigiously. We have also studied the UV-vis properties as well as fluorescent properties of these newly prepared porphyrins with different functional groups attatched on the meso-position and the results show the electron density on porphyrin core is strongly affected by these heteroatoms.