Preparation And Stimulus Response Of Gels And Crystals Based On Uracil

Stimulus-responsive materials are intelligent materials that can undergo physical or chemical changes in response to external stimuli and have important applications in the fields of fluorescent probes,optoelectronic devices,drug delivery,etc.Small-molecule stimulus-responsive materials,which have the advantages of simple structure,easy synthesis,rapid response and high resolution,have attracted attention.Uracil derivatives are an important class of small molecules with many advantages:1)Uracil is one of the nucleoside bases and its derivatives have good biocompatibility and very low toxicity,and have been used in cell imaging and fluorescent probes.2)It has been reported that[2+2]cycloaddition may occur in the double bond of uracil ring under UV irradiation,so uracil derivatives may have photo-responsive properties.3)Uracil molecules are easy to be modified 4)Uracil have good hydrogen bonding units,which facilitates the self-assembly of the molecule.The development of multi-stimulus responsive materials based on uracil derivatives has important research implications.Based on the above considerations,in this thesis,we designed and synthesized a series of uracil derivatives,studied their photophysical properties,self-assembly properties and stimulus response,and obtained results are as follows:(1)Uracil derivatives(NOB-3,NOB-4,NOB-16,NSB-8 and NSB-16)modified by benzothiophene and benzoxazole,were designed and synthesized.It was found that NOB-8,NOB-16,NSB-8 and NSB-16 can form gels in the mixture of alcohol and water.In particular,NOB-16 exhibited excellent gel-forming properties with a minimum gel-forming concentration of 1.2 mg/m L in isopropanol/water(v/v=4/3).According to the single crystal structure of NOB-16,UV-vis absorption spectrum and fluorescence spectrum during gel formation,as well as IR spectra and XRD test results of xerogel,the driving forces of NOB-16 gelation include van der Waals force,hydrogen bond andπ-πinteraction.Interestingly,gel of NOB-16 collapsed when exposed to 365nm UV light.~1HNMR of gels before and after light irritation demonstrated that the[2+2]cycloaddition between pyrimidine double bonds was responsible for the gel collapse.The fluorescence of NOB-16 xerogel film could be quenched by volatile acid,and its fluorescence was completely quenched in saturated TFA vapor in only 0.58 s.While the fluorescence of the solution was enhanced after the addition of acid.The difference response to acid of xerogel film and solution in different states was discussed based on the structural characteristics of the molecules:the NOB-16 molecule in the xerogel was protonated,ICT occurred,and the fluorescence was quenched.While the NOB-16molecule in solution was protonated and intermolecular hydrogen bonds were formed the rigidity and plane of the molecular was enhanced,and its fluorescence emission was enhanced.The NOB-16 gel was prepared as a developer for latent fingerprints imaging,and distinct photographs of latent fingerprints were obtained.(2)Diarylethene derivatives based on uracil:Z-NES-4,Z-NES-8,Z-NEO-8,Z-NEPh5F-8,E-NEPh F-8 and E-NES-8 were designed and synthesized.It was found that Z-NES-8 has good photo-response ability.First,its fluorescence emission intensity was significantly enhanced after irradiated by UV light.The results of ~1H NMR spectrum before and after illumination showed that when the solution of Z-NES-8 was exposed to UV light,it underwent cis-trans isomerization and aromatization after electrocyclization,respectively.In addition,Z-NES-8 crystals cannot emit fluorescence,and the fluorescence of the crystals was turned on after UV light illumination due to the gradual conversion the Z-configuration to E-configuration by cis-trans isomerization.With the prolonged light exposure time,the fluorescence emission of the crystal is gradually enhanced and the Z-NES-8 crystal undergoes photomechanical motion,such as blowing up,peeling,and bending toward the light.The results of ~1H NMR spectrum before and after UV irradiation and single-crystal structure of Z-NES-8 crystals indicate that the molecules undergo cis-trans isomerization in the crystals,upon light irradiation,which resulted in the enhanced fluorescence and photomechanical effects in crystals.