Molecular Design With AIE Properties And Properties Of Hydrogels

The use of fused-ring conjugated molecules with large planar structures in high concentrations and solid states is limited due to the phenomenon of fluorescence quenching in the aggregated state,while non-planar conjugated structures with twisted structures exhibit the resulting fluorescence intensity-enhanced aggregation-induced emission（AIE）phenomenon solves this problem.After more than 20 years of development,materials with AIE properties have great application prospects in the fields of optoelectronic materials,chemical sensing,smart materials,and biological probes.The design and synthesis of AIE molecules with novel structures and unique properties are in the ascendant.Fluorescent hydrogels based on AIE molecules have attracted much attention due to their ability to respond significantly to external stimuli,and have become a hot research topic.Due to its highly water-swellable quasi-solid state,it exhibits solid and solution properties,and has potential prospects in stimulus sensing,information encryption and decryption,and anti-counterfeiting applications.In this paper,based on the highly distorted characteristics of AIE molecules,the fluorene ring structure and the common simple condensed aromatic hydrocarbon structures（such as naphthalene ring,anthracene ring and phenanthrene ring）are combined and connected by double bonds through a simple synthesis method by molecular design.A series of novel diarylmethylene fluorene structures with asymmetric structure were prepared,and the luminescence color and efficiency of AIE molecules modified with different large sterically hindered side groups were studied in solution and solid,and their stimuli-responsive properties were explored.The relationship between the molecular packing state and the new AIE molecules were further combined with the hydrogel to prepare a multi-responsive fluorescent hydrogel.First,the skeleton structure of 9-benzylidene-9H-fluorene derivatives was designed and synthesized,and the fused ring aromatic hydrocarbons（such as naphthyl,phenanthryl and anthracenyl）were twisted and modified by Suzuki coupling method to obtain a series of asymmetric diarylmethylene fluorene derivatives with AIE properties.The structure of the product was analyzed and confirmed by NMR and FT-IR data,and the emission color and AIE of the three series of products were analysis the performance by UV-Vis spectroscopy,solid fluorescence,fluorescence photo of the product under UV lamp,liquid fluorescence and molecular orbital theoretical calculation.After characterization analysis,it was found that the three series of products all have AIE properties,and because of the large steric hindrance of anthracene and phenanthrene in the structures of anthracene and phenanthrene series,the products of anthracene and phenanthrene series are more red shift phenomenon than those of naphthalene benzene series.When the substitution positions of the naphthyl groups in the three series of products are different,the fluorescence colors are not quite the same,indicating that we can control the emission colors of the products by changing the substitution positions.Secondly,the new AIE products were screened to explore the mechanical,solvent,temperature and ion detection responses of the synthesized AIE molecules.It was found that 1-FNA,the product of anthracene series,not only exhibited two different luminescence colors in amorphous and crystalline states,but also exhibited obvious crystallization-induced fluorescence enhancement.The 1-FNP in the phenanthrene series and the 9-FPA product in the anthracene series have obvious mechanical grinding discoloration response,and 1-FNP can also realize the reversible conversion from grinding to fuming,and through the comparison of different solvent steam fuming was found that the better the solubility of1-FNP in good solvent,the closer the recovered product structure is to the original product.The 9-FPA not only exhibits different luminescence colors under different stimuli such as pressure,solvent vapor,and temperature,and can achieve rapid conversion from yellow to cyan,but also has a specific and high-sensitivity response to Fe³⁺.The minimum detection limit of the fluorescent solution was analyzed,and the minimum detection limit of 9-FPA for Fe³⁺was 1.16*10^-4 mol/L.By analyzing the XRD of the stimulated samples,it can be obtained that the luminescence colors of the stimulated samples are different because of the conversion of the molecular packing state inside the crystal under the action of different stimuli.This multi-stimuli-responsive property has broad application prospects in the fields of anti-counterfeiting materials,detection,and sensing.Finally,the selected novel AIE molecules 1-NPF and 2-NPF with excellent luminous efficiency were respectively polymerized with acrylamide to prepare novel AIE fluorescent hydrogels.By adjusting the ratio and concentration of water/organic solvent inside the fluorescent hydrogel,multiple groups of gel samples with different luminescence colors and brightness were prepared,and the luminescence properties were analyzed and the ion switch response was detected.Processed into a fluorescent aerogel,it can respond more quickly to ion switching.At the same time,fluorescent hydrogels also have potential applications in anti-counterfeiting and decryption.