Design And Synthesis Of Polysaccharide Polysaccharides With Polychromatic Tunable Solid-state Fluorescent Molecules

Since the emergence of multi-color tunable solid-state fluorescent materials,due to their"more aggregated,more luminous"characteristics,high photoelectric efficiency,fast molecular response,and good molecular skeleton flexibility,they have been widely used in organic optoelectronics,cell imaging,chemical detection,anti-counterfeiting,fluorescent sensors and other fields.However,the traditional light-emitting group molecular skeleton has strong conjugation,which easily leads to fluorescence quenching.In addition,their preparation process is complicated and cumbersome,poor processability,high biological toxicity and other problems further affect the rapid development and wide application of such fluorescent materials in the fields of chemistry and biomedicine.With the effective control of the chemical structure(conjugation structure,substituted side groups,element composition or molecular polymerization degree,etc.)and microstructure(aggregation,crystalline state and nanoparticle size,etc.)of new luminescent materials,a full range of color fluorescent materials and full-color adjustable dynamic fluorescent materials.Although these results are exciting in the field of new energy materials,the future tunable multicolor fluorescent materials will always face many challenges.This includes:(1)Under the premise of the same molecular structure,it is difficult to achieve multicolor fluorescent materials excited by a single wavelength;(2)It is not possible to simultaneously study the multicolor of non-conjugated polymers through chemical synthesis.The light-emitting mechanism of fluorescent materials;(3)The large-scale control of the light-emitting wavelength in the same molecular structure is relatively limited;(4)Some fluorescent materials are difficult to degrade and easily cause environmental pollution.Bio-based non-conjugated organic fluorescent materials,due to the advantages of strong structural design,flexible material processing,good biocompatibility,and low toxicity,have gradually received extensive attention from scientific researchers.Since 71%of the earth's surface is the ocean,there are many types of renewable marine plants(such as seaweeds,etc.)and they multiply fast.Natural polymer materials extracted from seaweeds have been widely used in food,medicine and other fields.At the same time,the preparation of marine biomass fluorescent polymer materials by a controllable synthesis method is also one of the important ways to establish a renewable marine energy system.Therefore,the design of a new type of light-emitting unit with high fluorescence efficiency and simple synthesis process,and the development of an excellent class of tunable multicolor fluorescent materials based on marine biopolysaccharides have great scientific significance for the development of life sciences,chemistry,chemical engineering,and medicine.Sodium alginate is a natural polymer polyelectrolyte extracted from natural brown algae,which has the advantages of good biocompatibility and easy biodegradation.The functional groups of sodium alginate itself can also be chemically modified,and the intramolecular hydrogen bonding makes it have a stable clustered conformation,which provides an excellent framework material for aggregation-induced luminescent materials.In this thesis,sodium alginate is used as the skeleton,and sodium periodate is used to oxidize to obtain a functionalized polysaccharide structure(OSA)containing aldehyde groups,and then undergo Schiff base reaction with small organic molecules containing amino groups to regulate their fluorescence color and luminescence properties.The conformation of small molecules and the influence of steric hindrance on the fluorescence properties have been studied.The specific research contents are as follows:(1)OSA-3-Apy and OSA-5-Apy multicolor tunable solid-state fluorescent materials were prepared by grafting two isomers of 3,3'-diamino-2,2'-bipyridine(3-Apy)and 5,5'-diamino-2,2'-bipyridine(5-Apy)onto OSA through chemical reaction.The research results show that by adjusting the types and cross-linking ratio of the two isomers,a blue-green-yellow multicolor tunable solid-state fluorescent molecule has been developed.Compared with OSA-5-Apy,OSA-3-Apy exhibits a red-shifted ultraviolet-visible absorption spectrum,and its fluorescence quantum efficiency(?_f)reaches 15.36%,and its fluorescence lifetime(?)is 12.38 ns,which is significantly higher than OSA-5-Apy(?_f is5.25%,?is 3.61 ns).Theoretical calculation results show that the bipyridine twist angle of the fluorescent molecule OSA-3-Apy is 65.6°,which makes its configuration more stable,thereby reducing the loss of non-radiative energy and exhibiting better fluorescence performance.Through the analysis of fluorescent materials with different cross-linking ratios,it is found that the non-conjugated structure of the sodium alginate skeleton can enhance the solid-state luminescence.Moreover,after testing,it is found that the cross-linking of small molecules has the best ratio.When the cross-linking ratios of OSA-3-Apy and OSA-5-Apy are 1000:1 and 100:1,the fluorescence quantum efficiency is the highest.Using OSA-3-Apy and OSA-5-Apy,fluorescence imaging was successfully performed on L929 cells,Escherichia coli and Staphylococcus aureus.Both OSA-3-Apy and OSA-5-Apy passed through the cell membrane to stain the cytoplasm.And realized the directional observation of cells.Through calcium ion cross-linking experiments,it is found that OSA-3-Apy still has fluorescence emission at a concentration of 1000 ppm,while OSA-5-Apy is quenched at an ion concentration of 0-10 ppm.The different conformation of Apy in fluorescent materials leads to different complexing effects with calcium ions.The two materials have good processing properties.Fluorescent fibers and gels with three fluorescent colors of yellow,green and blue were prepared,indicating that the sodium alginate-based fluorescent material has potential application value in chemical probes,anti-counterfeiting,biological imaging and other fields.(2)In order to obtain solid-state fluorescent materials with high fluorescence quantum yield,on the basis of the first part,through fine-tuning of the small molecular structure,OSA-2-Dby and OSA-4-Dby high-efficiency fluorescent materials were prepared by grafting two isomers of 2,2'-diaminobiphenyl(2-Dby)and 4,4'-diphenyl(4-Dby)without N heteroatoms onto OSA.NMR and FTIR results show that 2-Dby/4-Dby was successfully cross-linked to the sodium alginate backbone.OSA-2-Dby and OSA-4-Dby exhibit blue and cool white fluorescence,respectively.The analysis shows that the charge distribution in the perphenyl cyclic biphenyl molecule is uniform,which is more excellent than that of aminobipyridine molecule.The fluorescence efficiency of OSA-2-Dby and OSA-4-Dby are as high as 32.33%and 31.17%,respectively,which is equivalent to twice the OSA-Apy material.And OSA-Dby is a single-component multi-emission material,which not only has solid-state fluorescence,but also exhibits room temperature phosphorescence.The phosphorescence lifetime was tested,and the phosphorescence lifetimes of OSA-2-Dby and OSA-4-Dby were as high as 4.41 ns and 3.36 ns,respectively.2-Dby has an enhanced effect on phosphorescence.By shooting with a high-speed camera,the room temperature phosphorescence of OSA-2-Dby is as long as 6 s,while the occurrence of room temperature phosphorescence is not observed in OSA-4-Dby.(3)The steric hindrance effect of small molecules can improve the fluorescence efficiency and make the fluorescent material produce red shift.This part increases the steric hindrance of small molecules on the basis of the second part,and explores the effect of cross-linking of small molecules with amino groups with different steric hindrance on fluorescent materials.OSA-p-Pld,OSA-T3AM,OSA-T4AM fluorescent materials was prepared by cross-linking p-phenylenediamine(p-Pld),tris(3-aminophenyl)methane(T3AM),and tetra(4-aminophenyl)methane(T4AM)to OSA.OSA-p-Pld,OSA-4-Dby,OSA-T3AM,OSA-T4AM exhibit yellow,cool white,yellowish green and green fluorescence respectively in solid state.The fluorescence emission wavelength of OSA-T3AM and OSA-T4AM is blue-shifted.The research results show that under the same test conditions,as the number of benzene rings increases,the steric hindrance of small molecules increases,and the fluorescence intensity of OSA-p-Pld,OSA-4-Dby,OSA-T3AM,and OSA-T4AM respectively reach 3.6×10~5,1.4×10~7,9.6×10~5 and 2.6×10~6.With the increase of steric hindrance,the fluorescence intensity presents a trend that first increases,then decreases and then increases.The small molecules of biphenylamine show stronger fluorescence enhancement.Increasing steric hindrance can result in better conjugation,which can enhance fluorescence to a certain extent,but the free rotation of the benzene ring consumes most of the energy and weakens fluorescence emission.