Syntheses And Properties Of Six-or Seven-Membered N-Heterocycle Fused Porphyrin Dimers

Porphyrin,an 18πaromatic macrocyclic system,is consisted by four pyrrole units and four bridging carbon atoms.By modifying the porphyrin periphery or core in the controlled way,the precise regulation of the electronic and spatial structure of porphyrin can be realized,resulting in new application value which can be appreciate.Introducing heteroatoms or heterocycles into porphyrin is considered as one of the most effective ways to construct porphyrin-based new functional materials,which can induce or improve many desirable properties,such as dramatically electronic,optical,and electrochemical properties.It is well known that the study on preparation of five-or six-membered heterocycle fused porphyrins is very common.Because the formation of five-or six-membered rings is superior to that of seven-membered rings in both thermodynamics and kinetics.For another,the study of porphyrin analogues in which one or two pyrroles were replaced with nonpyrrolic building blocks might shed light on the correlation between structural modulation and ground and excited state optical properties,unlocking their mechanisms of function and exploring their new properties.Based on the above reasons,embedded heterocycles,seven membered nitrogen heterocycles especially,into porphyrin periphyery or syntheses of pyrrole modified porphyrins（PMPs）have become an important opportunity and challenge in the field of porphyrin chemistry,simultaneously,it is necessary to develop some new methods and technologies to synthesize these novel porphyrins.In this thesis a series of seven-membered N-heterocycle fused porphyrin dimers have been prepared.On the other hand,simultaneous implementation of N-heterocycle-fused bridge and modified pyrrole unit on porphyrin dimers has been achivemented by empolying a simple and efficient strategy to obtain three unprecedented（PMP）-porphyrin dimers.Their structures were characterized by NMR,X-ray crystallographic analysis and Matrix-assisted laser desorption ionization time-of-flight（MALDI-TOF）mass spectrometry,and their photophysical and electronic properties were studied by ultraviolet-vis（UV/Vis）absorption spectra,cyclic voltammetry（CV）and differential-pulse voltammetry（DPV）experiments and time-dependent density functional theory（TD-DFT）calculation.These works mainly included the following contents:（1）A brief overview on PMPs and porphyrins fused by nitrogen N-heterocycle（s）in recent decades.（2）Employingβ-βlinked meso-aminoporphyrin as starting material,a series of novel seven-membered N-heterocycle fused porphyrin dimers were synthesized by Pictet-Spengler reaction.A subsequent oxidative fusion reaction mediated by FeCl₃ and DDQ allowed for the synthesis of expandedπ-conjugated porphyrin dimers.The X-ray crystallographic analysis revealed that the two porphyrins in 2d-Ni were symmetrical and almost parallel to each other with a dihedral angle of 0.00（9）^o.However,a dihedral angle of the two porphyrins in 2e-Ni was 18.89（19）^o,which indicated that the structure of 2e-Ni was more twist than that of 2d-Ni due to undesired intramolecular oxidation.The obvious red shift Q-like bands of these seven-membered N-heterocycle fused porphyrin dimers indicated that the conjugation systems were obvious extended.Meanwhile,oxidation ofβ-βdirectly linked meso-aminoporphyrin dimer2c with PbO₂ gave an unexpected helical tetrapyrrin（biliverdin analogue）-fused porphyrin 4a-Ni whose properties were also discussed.（3）Inspired by above results,changing the connection fashion of aminoporphyrin,a different result was obtained.Oxidation ofβ-to-meso directly linked aminoporphyrin 5c with PbO₂ or MnO₂,leaded to three PMP-porphyrin dimers 6a,7a,and 8a successfully,in which the mechanisms was discussed preliminarily.The UV/Vis absorption spectra indicated that the different N-heterocycles brought about different effects on the structural and electronic changes of the PMP and porphyrin moieties.Moreover,the CV and DPV experiments and TD-DFT calculations results were consistent with their UV/Vis absorption spectra results,and the electrochemical gaps of the HOMO-LUMO of 6a-9a were 1.37,1.29,1.66,1.73 eV,respectively.