A Study Of An All-organic Electrochemiluminescence System Based On A Thermally Activated Delayed Fluorescence Mechanism

Nowadays,electrochemiluminescence has emerged as an indispensable bioanalytical detection method with widespread applications in analytical chemistry,environmental assays,food safety,imaging analysis,immunoassay and bioscience.ECL based on organic luminophore is persistently being pursued owing to its merits of low cost,simple synthesis and lower toxicity.Unfortunately,on account of theoretical limit in radiative excition generation yield（typically～25%）of conventional organic luminophore,the maximum ECL efficiency(_ECL)is only 25%,which hampers its ECL performance and applications.Therefore,it still remains challenges to develop novel organic luminophore with high ECL efficiency.In this dissertation,three kinds of organic luminophores based on thermally activated delayed fluorescence mechanism were developed,and their photophysical,electrochemical and electrochemiluminescence properties were investigated.This dissertation mainly includes the following three parts:（1）ECL study of TADF conjugated polymer PCz ATDx based on poly（3,6-carbazole）backboneIn this work,ECL properties of four TADF conjugated polymers（PCz ATDx）based on poly（3,6-carbazole）backbone with different emitting monomer content（x）were studied.The TADF characteristics of PCz ATDx polymers were confirmed by measurement of the transient photoluminescence（PL）decay spectra.The electrochemical and ECL test exhibited that PCz ATDx polymers could be electrochemically oxidized/reduced into positive/negative charged species,and the collision of them produced annihilation ECL.Furthermore,stable and efficient coreactant ECL were observed for PCz ATDx polymers with TPr A as coreactant.The ECL efficiency of PCZATD1,PCZATD5,PCZATD10 and PCZATD25 polymers were 2.48,4.47,5.65 and 1.54 times higher than that of Ru（bpy）₃²⁺,respectively.（2）Efficient cathodic ECL of TADF conjugated polymer based on poly（fluorene sulfone-alt-fluorene）backboneStable and efficient cathodic ECL derived from a novel TADF polymer（PFSOTT5）based on poly（fluorene sulfone-alt-fluorene）backbone was obtained in this work.With measurement of transient PL decay spectrum,PFSOTT5 polymer was disclosed to have TADF nature.ECL performance showed that not only PFSOTT5 polymer could produce annihilation ECL via collision of positive and negative charged species,but also it could generate efficient coreactant ECL with TPr A or BPO as coreactant.Compared with F8BT/BPO standard system,the cathodic ECL efficiency of PFSOTT5/BPO was improved by 5.79 times.（3）Aggregation-induced delayed fluorescence luminogens for aqueous ECLHerein,we first proposed to construct aqueous ECL based on aggregation-induced delayed fluorescence luminogens,called AIDF-ECL.The m CP-BP-PXZ luminogens were successfully synthesized by nanoprecipitation method in THF/water system.As increasing the water fraction（f_w）value,PL peak intensity was monotonically enhanced and delayed fluorescence excition lifetime（τ_d）was largely increased,which revealed the AIDF nature of m CP-BP-PXZ luminogens.ECL emission of AIDF luminogens was investigated in aqueous solution and the results showed that the ECL characteristics were directly related to their AIDF properties.Compared with an aggregation-induced ECL（AIECL）control sample,the ECL efficiency of our AIDF-ECL model system was improved by 5.4 times.