Electrochemical Luminescence Performance And Analytical Application Of Rigid Silole Organic Small Molecules

Silole is a class of five-membered heterocyclic compounds containing silicon.Compared with other five-membered heterocyclic compounds,silole has a narrower band gap（HOMO-LUMO）and the lowest LUMO energy level.Theσ*-π*conjugated structure formed between the extra-cyclicσ*orbital and theπ*orbital of butadiene makes silole compound have stronger electron-absorbing ability.It shows good electron transport and luminescence performance.Electrochemical luminescence（ECL）is a unique luminescence phenomenon that generates excited species during the redox process of the luminescent material.These excited species emit energy in the form of light when they relax to lower energy states.ECL luminescent body is the key factor of ECL method,which directly determines the strategy and efficiency of ECL application.Therefore,the establishment of a general and efficient luminescent system is an important means to improve the electrochemical luminescence sensing and analytical capability.At present,it is rare to study small organic silole molecules with rigid skeleton as ECL luminescent bodies in water phase,and most of the reported electrochemical luminescence studies of silole compounds focus on organic phase,which limits its practical application.Therefore,this paper focuses on the electrochemical luminescence performance and application of silole compound with rigid skeleton in aqueous phase.We have carried out the following three parts of work:Part Ⅰ:Electrochemical Luminescence of different substituent-modified spirocyclic silole derivatives for the detection of Cl O₄^–In this part of work,spirocyclic silole derivatives with electron-withdrawing substituents（-NO₂）and electron-donating substituents（-NH₂）were synthesized by substituent modification strategies,which were 3,3’-dinitro-5,5’-spirobi[dibenzo[b,d]silole]（SBDBS-（NO₂）₂）and 3,3’-diamine-5,5’-spirobi[dibenzo[b,d]silole]（SBDBS-（NH₂）₂）,respectively.Spectroscopic characterization and electrochemical tests showed that SBDBS-（NH₂）₂ had the largest fluorescence emission wavelength and a more positive reduction potential.When potassium persulfate was used as a coreactive agent,the substituent-modified spirocyclic silole derivatives had higher ECL emission than spirosilole monomer.Thereby SBDBS-（NH₂）₂ was selected as the best ECL luminophores.Because SBDBS-（NH₂）₂ shows good reduction performance,perchlorate（Cl O₄^–）with strong oxidation ability can capture electrons during SBDBS-（NH₂）₂ reduction process,thus inhibiting ECL emission of SBDBS-（NH₂）₂.Therefore,a kind of aqueous cathode ECL sensing platform for detecting Cl O₄^–was established.Part Ⅱ:Electrochemical luminescence of small organic molecules of fused ring silole and its application in determination of cysteineIn this part,the fused ring system is introduced into the silole ring,and theπsystem is expanded through aromatic cyclization to provide new properties for the silole skeleton.Such molecules have a rigid coplanar structure,resulting in strongπ-πinteractions between solid phase molecules.Three small organic molecules of fused ring silole were synthesized,dinaphthalenesilole（DDNS）,dithiophensilole（DDTS）and dibenzosilole（DDBS）,respectively.The theoretical calculation and experimental results show that DDNS is the best luminophores because of its low LUMO energy level,narrow band gap（HOMO-LUMO）and easy reduction potential.Since the sulfhydryl and carboxyl groups in cysteine are effective free radical quenching agent,they can react with SO₄^·-to reduce the concentration of SO₄^·-,thus inhibiting the emission of ECL.A sensor for detecting cysteine was constructed.Part Ⅲ:Electrochemical luminescence properties of triphenylamine modified benzosilole moleculesIn this part,benzosilole（DDS）is selected asπ-conjugated bridge,and triphenylamine（TPA）with strong electron donor ability is used as electron donor to form a molecular structure of donor-π-donor,namely DDS-TPA.The structure effectively extendsπ-conjugated system,and after the triphenylamine group is conjugated with benzosilole,the HOMO-LUMO band gap of DDS-TPA decreases significantly,and the LUMO energy level also decreases significantly.These advantages are easy for DDS-TPA to obtain electrons,and electron transfer reaction occurs.This is the main reason for the ECL enhancement of DDS-TPA.These results are conducive to further research on the influence of molecular structure on electrochemical luminescence performance,and provide ideas for exploring more organic ECL luminophores.