Design,Synthesis And Luminescence Properties Of Organic Fluorescent Materials Based On Cyanostyrene And Benzothiophene Sulfone

Organic fluorescent materials have attracted extensive attention of scientists and have been used in many fields such as opto-electronic devices,bioimaging,interface visualization due to the advantages of easy modification of structure,adjustable fluorescent color and low cost.In the field of biological imaging,the imaging penetration depth is highly restricted due to the self-luminescence and the light scattering in biological tissues,which limited the utilization of organic fluorescent materials for in vivo imaging.Although organic fluorescent materials play an important role in the field of visualization to polymer properties and structures,there are currently very few fluorescent probes available for various visualization tasks.More available organic fluorescent material systems need to be developed.Additionally,most luminescent materials are aggregate in applications.For organic fluorescent materials,their fluorescent properties in solid-state not only depend on the structure of the molecules but are largely affected by the packing mode in aggregate.Therefore,it is essential to understand the relationships between the molecular stacking modes and fluorescence properties at molecular level in order to obtain materials with the desired properties for bioimaging and polymer visualization.Herein,this dissertation synthesized a variety of organic fluorescent materials,and studied their optical properties.Based on the effects of aggregation state and stacking structure on the fluorescent properties of materials,the relationship between the fluorescence properties and the aggregation mode of organic fluorescent materials in polymers was explored.And these materials were applied in the fields of bioimaging and the visualization of phase structure in polymer blends.The specific research contents are as follows:1.A series of cyanostyrene derivatives were designed and synthesized,named DPB,DOB,DTB,DTTB,respectively.By manipulating the electron donating ability of the side groups,a molecule with high-brightness and near-infrared emission in solid state was obtained,DTTB(712 nm,ΦF=14.2%).In order to make DTTB have good biocompatibility and application in bioimaging,we encapsulated it with amphiphilic polymers.In the process of preparing nanoparticles,the unique fluorescence enhancement of DTTB by benzene ring-containing polymers was found.The experiment proved that this special fluorescence enhancement phenomenon originated from the effective restriction of DTTB molecular vibrational motion by benzene ring-containing polymers.In addition,DTTB@PS-PEG NPs have a large two-photon absorption cross-section under800-1050 nm laser excitation.Thus,we obtained DTTB@PS-PEG NPs with high-efficiency near-infrared luminescent(ΦF=29.8%)by using the special luminescent properties of this series of molecules in polymers.Subsequently,we performed two-photon fluorescent imaging on Hela cells with the DTTB@PS-PEG nanoparticles and obtained a high fluorescence signal,indicating that cyanostyrene derivatives have great application prospects in the field of two-photon bioimaging.This work provided a reference for the design of two-photon fluorescent probes with high-brightness and near-infrared emission.2.The special fluorescent properties of cyanostyrene derivatives(TB)in different polymers were studied.Under the irradiation of ultraviolet light(365 nm),TB doped in polymers containing benzene rings,such as polystyrene(PS),exhibited strong near-infrared fluorescence emission(610 nm,ΦF=21%).However,when TB was doped in polypropylene(PP)and other polymers without a benzene ring,the fluorescence was almost quenched(656 nm,ΦF<1%).Through the research from steady-state/transient spectroscopy and theoretical simulation,it was found that the special luminescence properties of TB in different polymers stem from the different compatibility of TB: TB doped in PS tended to be isolated and TB doped in PP tend to aggregate.Owing to the specific fluorescence behavior of the cyanostyrene derivative TB,the high-contrast imaging of polymer blendsphase in two and three dimensions can be achieved by multiphoton laser scanning microscopy(MLSM).Furthermore,in situ visualizations of internal morphology deformation and macrophase transformation were realized by employing a stretching dumbbell sample under constant tension.Invisible information such as internal morphological changes of polymer samples were converted into visible fluorescence signals,which broadened the application of fluorescence microscopy in polymer research and provided a more convenient and accurate method for the study of polymer.3.The benzo[b]thiophene 1,1-dioxide(BTO)derivatives BTO-TF,BTO-OH and BTO-N were designed and synthesized.We manipulated the molecular cycloaddition ability by changing the side groups of molecules.The study found that due to different molecular packing structures,these materials had different topological [2+2] cycloaddition abilities in solid state and exhibited different degrees of fluorescence changes under UV light irradiation.The crystallographic analysis and theoretical investigations indicated that the fluorescence switching and enhancement originated from the destruction of [2+2] cycloaddition by the volume expansion of the dimer.Based on the research in the second part of the work,the stacking mode was manipulated by polymers,so that benzothiophene sulfone derivatives exhibited different cycloaddition abilities in different polymers accompanied by changed in fluorescence.The visualization of the phase-separated structure of PS/polyhexamethylene(PCL)films was realized,which provided a new strategy for the design of fluorescent probes to visualize phase separation of polymer blends.