Construction Of Near-infrared Dyes By C-H Activation

Bioluminescence imaging technology based on fluorescent dyes is one of the most important tools in fundamental biomedical research.This technique is used to monitor biological tissues and cells in real time with simple operation.It has become a hot topic in clinical medical diagnosis and biological research.The near infrared(NIR)fluorescence imaging technology is of particularly importance because it further reduces the influence of the spontaneous fluorescence from organism tissue,thus improves the penetration depth and ability of optical imaging,reducing the loss of light to a greater extent.All these biological imaging technologies are based on obtaining good fluorescent dyes.NIR dyes refer to an important class of functional dyes that emit the NIR(wavelength>700nm)light,meanwhile vibrates in the NIR range.Compared with inorganic NIR fluorescent materials,research in organic NIR dye molecules is hot because of their high fluorescence quantum yield and better biocompatibility,as well as the flexibility in structure functionalization and modification,resulting in a tunable spectral range.Recent years,NIR dyes have been widely used in the fields of optical imaging,tumor diagnosis and fluorescence identification.However,the simple and efficient synthesis of NIR dye molecules is still a challenge and the focus of research in chemistry,material science and biology.When designing.and synthesizing NIR dyes,the synthetic steps should be decreased as much as possible for a quick and simple construction of target molecules.Hydrogen bond activation is a new type of reaction that developed rapidly in recent years,showing great potential in the field of synthesizing NIR dyes with the advantages of atomic economy and environment-friendly.The transition metal palladium is used to catalyze the carbon hydrogen C-H activation,making it a very effective way for the construction of various molecules such as organic natural products and drugs.The guiding group coordination mechanism enables a one-step transformation of functional groups,with the breaking of C-H bond and the formation of C-C and C-X(X=N,O,Cl,Br,I,etc.)bonds,thus reducing the steps from the traditional synthetic processes,improving the efficiency of functionalization as well as the atomic utilization.In this work,three kinds of organic NIR dye molecules(boron-dipyrromethene,benzothiazole and Z dye)are explored and constructed by recently developed C-H activation reactions with simplicity.In the first part,the synthesis of boron-dipyrromethene(BODIPY)is attempted.With excellent photophysical property and designable structure,BODIPY is widely used in the diagnosis and treatment of tumors,therefore its design and synthesis is of great significance.In this part,the organic BODIPY dye molecules containing sulfur atom are prepared by catalyzing C-H and C-S alkynes thiophene using palladium catalysts,with the spectroscopic characterization carried out.In the second part,benzothiazole,a class of potential organic NIR dye with conjugated structure,are synthesized and modified using the hydrocarbon activation.As a result,two sulfur-containing benzothiazoles are obtained.In the last part,we try to design and synthesize a new class of NIR dyes,i.e.Z dyes.Although the dye molecules are partially obtained,this work demonstrates the great potential of hydrocarbon activation in constructing various organic NIR dyes.