Studies On The Synthesis And Properties Of Asymmetric Cyanine-like Dyes Containing Dioxanborine

Organic light-emitting materials are of great significance in the fields of biomarkers,biological imaging and organic light-emitting diodes（OLeds）.Cyanine dyes have become one of the most widely used organic luminescent materials due to their advantages of large molar absorption coefficient,relatively high stability,and wide tuning range of maximum absorption wavelength.However,cyanine dyes reported so far only have solution fluorescence.β-diketone boron fluoride complex（BF₂bdks）is a highly photoluminescent organoboron complex with strong fluorescence in solution and solid state.Biβ-diketone boro-fluoride complex has a large conjugated syste m and photophysical properties similar to cyanine dyes.Therefore,cyanine dyes andβ-diketone boro-fluoride complex can be heterozygozed to obtain new fluorophore with better properties.So far,some symmetrical and asymmetric cyanine dyes containing dioxazoborine have been synthesized with excellent properties,but most of these dyes are solution fluorescence,and the structure and photophysical properties of asymmetric monomethyl cyanine dyes Cy1containing dioxazoborine have not been reported.In the previous study of this paper,a new type of asymmetric cyanine dye containing dioxazoborine was designed and synthesized,and one end of the cyanine dye was replaced byβ-diketone boron fluoride complex,to obtain a new asymmetric cyanine dye CyBFdk-A1,which is connected by polymethyl-methyl chain with one end being N methyl onium salt and the other end being boron fluoride complex.Different from the solution fluorescence of traditional cyanine dyes,the new cyanine-like dye CyBFdk-A1 solution has almost no fluorescence,but shows obvious solid fluorescence in the aggregation state.The traditional research on aggregation-induced luminescence mechanism is usually carried out by changing the external environment and the structure-activity relationship,which is not only complicated in operation,but also poor in applicability.So far,more and more researchers have used theoretical calculation to reveal the excited state characteristics of aggregation-induced luminescence molecules so as to elaborate their luminescence behavior.In this study,the aggregation induced luminescence characteristics of CyBFdk-A1 were taken as the entry point,and the photophysical properties,molecular orbital,energy level transition,AIE mechanism,crystal structure and other aspects of CyBFdk molecules were systematically and deeply studied.In Chapter 2,the structure of CyBFdk-A1 was expanded to synthesize A series of novel asymmetric cyanine dyes CyBFdk-A1-4 with only one methygroup（n=1）in four conjugated chains,and B series of novel asymmetric cyanine dyes CyBFdk-B1-4 with three methygroups（n=3）in four conjugated chains.The UV-visible absorption spectra,fluorescence emission spectra,fluorescence quantum yield and fluorescence lifetime of eight CyBFdk compounds in solution and solid were systematically tested.Series A compounds were identified as aggregate induced luminescence（AIE）molecules,and showed high fluorescence quantum yield of solid fluorescence emission.By comparing the photophysical properties of series A and series B,the influence of conjugated chain extension on the photophysical properties of cyanine-like dyes can be known.The difference of photophysical properties of series A/B can be explained by theoretical calculation.The asymmetric cyanine-like dyes synthesized are identified as A-π-A type molecules by electrostatic potential analysis and segment charge transfer analysis.The method of potential energy curve scanning was used to explain the solution fluorescence quenching phenomenon of series A compounds,and QM/MM was used to explain the bright solid fluorescence in solids.Finally,crystallographic analysis was carried out to further explain the reason of high solid fluorescence of CyBFdk-A series molecules.In Chapter 3,the effects of the introduction of asymmetric cyanine-like dyes with phenyl rotors on photophysical properties are studied.In this chapter,four cyanine-like dyes of CyBFdk-C series were obtained by introducing phenyl group at the terminal methyl ofβ-dione boron difluoride complex.The introduction of phenyl makes the absorption and emission wavelengths of C-series appear red shift compared with those of A-series solution and solid,and the red shift of solid emission is more obvious.The solid emission wavelength of CyBFdk-C4 is 700 nm,which is A near-infrared aggregation induced luminescent molecule.According to the photophysical properties of A/C series,it can be realized that the regulation of AIE molecules from medium and short wavelength to near infrared AIE molecules can be realized by changing the heterocyclic ring of cyanine segment or introducing phenyl group into the methyl group at the end ofβ-diketone boron fluoride complex.According to TD-DFT calculation,the introduced phenyl rotor is coplanar with the molecule,and the benzene ring does participate in the conjugated system of C-series molecules,reducing the energy gap between HOMO and LUMO,resulting in redshift.The potential energy curve scanning study found that the reason for fluorescence quenching of CyBFdk-C series compounds in solution is different from that of series A.Single crystal analysis elucidates the causes of solid state fluorescence emission.In Chapter 4,based on CyBFdk-A1,four kinds of asymmetric rigid cyanine-like dyes CyBFdk-D1-4 with different sizes and positions of rigid rings are introduced.Different positions of rigid rings have a great impact on the absorption and emission properties of solutions and solids,especially for CyBFdk-D4,due to the limitation of rigid rings and molecular accumulation,Its solid emission wavelength is highly redshifted,reaching long wavelength emission of 676 nm.It belongs to red/near-infrared AIE molecule,which is of great significance for the subsequent application in the field of cell imaging or OLED.Then theoretical calculation was used to explain why different ring locations and sizes would have an impact on the photophysical properties.Potential energy curve scanning was used to study the reason why CyBFdk-D series compounds had almost no fluorescence in solution.Single crystal analysis was used to elucidate the reason of solid fluorescence emission.To sum up,the significance of this project is not only to design and synthesize a cyanine-like aggregates induced luminescence material with novel structure and carry out a series of structural expansion and property optimization.More importantly,based on this excellent aggregates induced luminescence material,the structure-activity relationship between molecules and AIE luminescence mechanism are discovered by theoretical calculation.This is of great significance for the inspiration brought by AIEgen structural design in the future and the expansion of AIE application.