Self-enhancing Electrochemiluminescence Materials From Porphyrin-based MOFs: Design,Synthesis And Synergistic Mechanism

Accurate detection and monitoring of the concentration of disease-associated biomarker is an important strategy for early detection and treatment of various diseases.Electrochemiluminescence（ECL）,an emerging technology combining electrochemistry and chemiluminescence,has become an effective tool for the detection of trace biomarkers in biological samples.Porphyrins and their derivatives are excellent building blocks for novel ECL materials due to their easy functionalization and high luminescence efficiency.However,porphyrins tend to form aggregates in aqueous solutions,making it difficult to fully expose their active sites,which limits the maximization of their optical properties and electrocatalytic ability.In this thesis,based on the structure and properties of zinc（Ⅱ）tetrakis（4-carboxyphenyl）porphine（ZnTCPP）,ZnTCPP was introduced into the metal organic frameworks（MOFs）as a functionalized ligand.Based on the physicochemical properties of ZIF-67（a complex of Co（Ⅱ）and 2-methylimidazole（MeIm））,ZIF-9（a complex of Co（Ⅱ）and benzimidazole（BIM））,MeIm,imidazole（Im）and BIM,through ligand exchange and ligand competition methods,a series of porphyrin-based MOF materials with highly dispersed active sites,high catalytic ability and excellent luminescence properties have been constructed.By integrating co-reaction accelerator and luminophore,the energy loss has been reduced and self-enhancing ECL has been obtained.Combining spectroscopic characterisation,electrochemical analysis and theoretical calculations,the structure-activity relationship between the structure of the porphyrin-based MOF materials and self-enhanced ECL performance has been investigated in depth.Based on the electron transfer and energy transfer modes in the ECL process,the ECL amplification mechanism has been elucidated.Based on the structure of the prepared porphyrin-based MOF materials and the corresponding ECL mechanisms,a novel sensing interface has been constructed to achieve rapid and sensitive detection of SARS-CoV-2.The main work and results of the thesis are as follows:1.Construction of the self-enhanced ECL emitter Co-MeIm-ZnTCPP induced by ligand exchangeIn traditional co-reactant ECL,the efficiency of the co-reactant catalyzed into an active intermediate is one of the dominant factors restricting the luminous intensity.In this work,Co-MeIm-ZnTCPP is designed as a composite material with the integrated co-reaction accelerator（Co-N）and luminophore.Through the catalytic effect of Co-N structures on hydrogen peroxide,the in-situ generation and accumulation of active intermediates are achieved,which will react with porphyrin anion radical,thereby bringing out self-enhanced ECL.By adjusting the scanning potential range,the ECL mechanism is thoroughly studied and the contribution of each potential window to the luminescence is obtained.This work provides inspiration for the design of inte-grated ECL emitters with co-reaction accelerator and luminophore,providing a new way for the construction of self-enhanced ECL emitter.2.Construction of an enhanced ECL emitter ZIF-9-ZnTCPP based on ECL-RET systemConstructing robust and efficient luminophores is important for the development of ECL amplification strategies.Inspired by the resonance energy transfer in natural light harvesting systems,we propose a novel ECL amplification system based on ECL resonance energy transfer（ECL-RET）,which integrates two luminophores,BIM and ZnTCPP,into one framework.Through the disassembling and reconstruction processes,numerous BIM surround ZnTCPP in the constructed ZIF-9-ZnTCPP.Combined with the overlapped spectra between the emission of BIM and the absorption of ZnTCPP,the energy of multiple BIM（donor）can be concentrated to a single ZnTCPP（acceptor）to amplify the ECL emission of the acceptor.This work provides a convenient way to design an efficient ECL-RET system,which initiates a brand-new chapter in the development of ECL amplification strategy.3.Construction of self-enhanced ECL emitter MOF1 based on the molulation of paddle-wheel units via axial coordinationHigh electrocatalytic activity with tunable luminescence is crucial for the development of ECL materials.In this work,a porphyrin-based heterobimetallic 2D MOF,[（ZnTCPP）Co₂（MeIm）]（1）,has been successfully self-assembled from the ZnTCPP linker and cobalt（Ⅱ）ions in the presence of MeIm by a facile one-pot reaction in methanol at room temperature.Based on the experimental results and the theoretical calculations,the MOF 1contains paddle-wheel[Co₂（-CO₂）₄]secondary building units（SBUs）axially coordinated by a MeIm ligand,which is very beneficial to the electron transfer between the Co（Ⅱ）ions and oxygen.Combining the photosensitizers ZnTCPP and the electroactive[Co₂（-CO₂）₄]SBUs,the2D MOF 1 possesses an excellent ECL performance,and can be used as a novel ECL probe for rapid non-amplified detection of the RdRp gene of SARS-CoV-2 with an extremely low limit of detection（～30 a M）.4.ECL of 2D porphyrin-based MOFs modulatd by imidazoles axial ligandsPrecise tuning the structure of catalytic center is of great importance for the construction of enhanced ECL materials and the development of ECL amplification strategies.In this section,a 2D heterobimetallic porphyrin paddlewheel framework（PPF）,a porphyrin-based MOF formed by the coordination of Co（Ⅱ）and ZnTCPP,is chosen as the substrate.Three imidazole-like ligands with different electron donating abilities,including MeIm,Im and BIM,have been introduced into the framework.The effect of the electron-giving ability of the three imidazole-like ligands on their axial coordination ability on the paddle-wheel units[Co₂（-CO₂）₄]SBUsis explored.In addition,the electrochemical and ECL behavior of PPF/X（X=MeIm,Im,BIM）with different axial coordination ligands are investigated in depth.