Synthesis And Study On Photoelectrochemical Properties Of Aggregation-Induced Emission Porphyrin

Porphyrins have been widely studied due to their excellent optical,electrical,and magnetic properties.As organic light-emitting molecules,porphyrin exhibits strong red fluorescence in dilute solutions,while fluorescence emission was very weak in high-concentration solutions.This was mainly owing to the formation of aggregates between porphyrin molecules through van der Waals force,hydrogen bonding,electrostatic force andπ-πinteraction.The porphyrin to form an aggregated precipitate in the aqueous solution caused by the hydrophobicity.In the application of porphyrin-photoelectric conversion devices,these aggregation behaviors lead to the weakening of porphyrin’s light-capturing ability and the quenching of excited-state electrons,and the decrease in photoelectric conversion efficiency.In addition,the sensitivity of porphyrin electrochemiluminescence（ECL）detection was reduced by the aggregation phenomenon.Therefore,the purpose of this paper is to improve the problem of quenching caused by porphyrin aggregation,and to synthesize luminous porphyrin molecules in aggregated state through molecular structure design.This molecule not only enhanced the light absorption properties and emission properties of porphyrin,but also realized the aggregation luminescence of porphyrin in aqueous solution,which makes up for the shortcomings of the aggregation quenching of traditional porphyrin molecules.The light-induced electron transfer kinetics was studied by photoelectrochemical testing and scanning electrochemical microscopy（SECM）,which satisfactory results have been obtained.The specific research content is divided into the following three aspects:（1）The different substituted aminoporphyrins and benzaldehyde-substituted tetraphenylethylene were synthesized.Porphyrin molecules with aggregation-induced luminescence properties were synthesized through Schiff base reaction,and used nuclear magnetic,mass spectrometry analysis to determine the chemical structure.The prepared materials produced strong red fluorescence emission in both solid state and aqueous solution.The photoelectrochemical tests showed that the photocurrent was significantly enhanced after the conversion of porphyrin to aggregation-induced luminescence.The photocurrent density of ATPP（TPE）₄ and ATPP（TPE）₁ are 1.08 mA·cm^-2 and 1.32mA·cm^-2,respectively.The porphyrins with AIE properties faster photo-excited electron transfer rate was proved by the technology of SECM and ultraviolet-visible light source,and the kinetic constants of ATPP（TPE）₄ and ATPP（TPE）₁ are 9.89×10^-2 cm·s^-1 and11.62×10^-2 cm·s^-1,respectively.This work will provide a new strategy to reveal the research of porphyrin photocatalysis and photosynthesis simulation.（2）The aggregation behavior destruction of metal porphyrin molecules and depolymerization to induce luminescence purposesuse was realized through axially coordinate of metal porphyrin and 4,4-bipyridine,this strategy can significantly improve the porphyrin fluorescence emission performance in the solid.The photoelectrochemical tests showed that the photocurrent density of（ZnTPP）₂bpy and（ZnTCPP）₂bpy are 0.88mA·cm^-2 and 0.96 mA·cm^-2,respectively.The photoelectron transfer kinetic information was verified by SECM.The photoinduced electron transfer kinetic constants of（ZnTCPP）₂bpy and（ZnTPP）₂bpy were 7.79×10^-2 cm·s^-1 and 6.14×10^-2 cm·s^-1,respectively.The research shows that the axial coordination connection of metal porphyrin is conducive to the electron mobility of porphyrin ring.This work provides new methods for constructing new porphyrin luminophores,and provides new research ideas for porphyrin photocatalysis.（3）The aggregated precipitates of porphyrin in water formation caused by hydrophobicity,which not only affects the luminescence performance,but also has limited applications in ECL biological detection and imaging.Therefore,it is of great significance to develop high-performance aggregated porphyrin phosphors.In this work,a highly efficient fluorescence emission in water environment was achieved by a synthetic aggregation-induced luminescent porphyrin,and the porphyrin aggregate/co-reactant system ECL was further studied.The results show that the ECL intensity of ATPP（TPE）₁in the aqueous phase reaches 17380 a.u.,which is 6 times stronger than that of ATPP,and has good stability.Theoretical calculation results show that the conjugation of the tetraphenyl vinyl group to the porphyrin reduces the molecule’s LUMO energy level（-2.858 eV）,making the molecule easier to obtain electrons during the reaction,and the energy band gap of HOMO-LUMO（1.708 eV）is also smaller than the energy band gap value of ATPP（2.676 eV）.The lower energy band gap is conducive to the occurrence of electron transfer reactions,which leads to a significant increase in the ECL of ATPP（TPE）₁.The ECL efficiency of ATPP（TPE）₁ was calculated to be 34.1%.This system successfully solved the application of hydrophobic porphyrins in aqueous ECL,and provides a new method for the study of porphyrin compound ECL bioimaging.