Synthesis And Properties Of Naphthalene-based Chalcone Gel Molecules

In recent years,researchers have expressed strong interest in low molecule organogels and their self-assembly.The self-assembly of low molecule organogels into a spatial structure with different microscopic appearances and sizes,and then forms a gel with a solvent due to exist intermolecular hydrogen bonding,coordination interaction,hydrophobic interaction,π-πstacking,van der Waals forces.Low molecule organogels have important application in fluorescent switches,sensors,drug transportation,and inorganic nanomaterial templates.In this paper,three series of chalcone organogel molecules based on alkyl chain substitution were designed and synthesized,and their gel properties,micromorphology and self-assembly mechanism were studied.The specific content is as follows:（1）The research progress of low molecule organogels are reviewed.The definition,classification,preparation methods,common characterization methods and applications of low molecule organogels are reviewed.At the same time,the latest progress of chalcone organogels are introduced in detail.（2）Anewchalconeorganogel（F₁）wassynthesized.Using2-Acetyl-6-methoxynaphthalene and 4-hydroxybenzaldehyde as starting materials,chalcone（M₁）was synthesised by aldol condensation reaction,and a new chalcone organogel（F₁）was obtained by long-chain alkyl-substituted benzoic acid esters was introduced into chalcone.The structure of the compound was confirmed by ¹H NMR,¹³C NMR,MS.The gelation behavior of the gel molecules F₁ was studied by inverted test tube method,they form organogels in n-butanol,n-heptane,acetone etc,and has very good stability in acetone.It is found by fluorescence spectroscopy that disassembly has been induced by the gradual addition of acetone,and the intensity of the peak was attenuated with a slight blue shift,which led to a decrease in fluorescence.It is found that the intermolecular hydrogen bond,the van der Waals force and theπ-πinteraction of gel molecules F₁ provide multiple driving forces for self-assembly into a lamellar network structure,and together with the solvent constitute a gel by SEM,FT-IR,XRD.（3）We synthesize three chalcone organogel F_2a-2c.Based on the M₁,the new chalcone organogel(F_2a-2c)were obtained by three alkyl chains of different lengths were introduced directly into chalcone（M₁）.The structure of the compounds was confirmed by ¹H NMR,¹³C NMR,MS.The gelation behavior of the gel molecules F_2a-2c were studied by inverted test tube method.The gel molecules F_2a-2c can form a stable gel in Cyclohexane,tert-butanol,isooctane,etc.The results for thermal stability showed that the alkyl chain length attached to the chalcone also had an important influence on the gelation behavior.More specifically,under identical concentrations increasing the length of alkyl chains of the gel molecules and then the gel-to-sol transition temperature value is increased too.It was found by fluorescence spectroscopy that the emission peak of the F_2b-tert-butanol system was red-shifted from 410nm to 440 nm with the increase of concentration,and the fluorescence quenched,indicating that the gel moleculeπsystem was enhanced while the gel formation processes aπ-πstacking occurs in the naphthalene ring.It was found by SEM that the dry gel of F_2a in the cyclohexane solvent has a rod-like network structure,the dry gel of F_2b in the tert-butanol solvent has a band structure,and the dry gel of F_2b in the isooctane solvent has a layered network structure.The results show that as the length of the alkoxy increases,the dry gel tends to exhibit a lamellar network structure.The mechanism of gel formation was verified by FT-IR and XRD,the self-assembly force of the gel was provided by intermolecular hydrogen bonding,van der Waals force andπ-πstacking.（4）ThetwochalconeorganogelF_3a-3bweresynthesized.First,6-hydroxy-2-naphthylethyl ketone and 9-anthraldehyde were used as raw materials.Chalcone was synthesized by an aldol condensation reaction,and the novel chalcone organogel(F_3a-3b)were obtained by two alkyl chains of different lengths were introduced into chalcone.The structure of the compounds was confirmed by ¹H NMR,¹³C NMR,MS.The gelation behavior was studied by inverted test tube method.It was found that the gel molecules F_3aa does not form a gel in all solvents,while the gel molecules F_3b can only form a gel in some alcohols,and has a very low critical gelation concentration in isopropyl alcohol with a melting temperature of up to 90°C.It was found by SEM,FT-IR and XRD that the self-assembly into a lamellar network structure driving force of gel molecules F_3b was provided by intermolecular hydrogen bonding,van der Waals forces,andπ-πstacking,and together with the solvent constitute a gel.