Preparation,fluorescence Emission Of Linear Aliphatic Amide Salts And The Emission Mechanism

Organic luminescent materials with adjustable emission have been widely used in the fields of optoelectronic devices,fluorescent probes and biological imaging.Traditional fluorescent compounds generally have large conjugated structures such as aromatic ring or aromatic heterocycle,and these large conjugated structures have high hydrophobicity and biotoxicity,which affect their applications in biological fields.Recently,many compounds without traditional chromophores have been reported,such atypical chromophores compounds only have traditional auxochrome such as tertiary amine,ester,carbonyl,hydroxyl and imide,but show"Aggregation-Induced Emission"（AIE）in nature,that is,fluorescence emission is enhanced in concentrated solution or at aggregate state.Compared with traditional fluorescent materials,the synthesis of atypical chromogenic compounds is simpler,and they have better water solubility and biocompatibility,so they are more suitable for many biological fields such as biosensors,cell imaging and drug delivery.At present,most studies of luminogens without typical chromophores focus on different polymers,and its luminescence mechanism is inconclusive.The studies of the luminescence mechanism require both explicit chemical structure and high purity of the materials.Therefore,it is of great interests to study the fluorescence mechanism of these fluorescent compounds,especially small molecule fluorescent materials.In this paper,the luminescence behavior and mechanism of aliphatic amide salt and polyamides were studied.The main contents are as follows:1.By simply blending methanol solution of aliphatic diamine with that of aliphatic diacid,the aliphatic amide salt was precipitated out.Nine amide salts were prepared by this way and their fluorescence properties were detected.As an example,ethylene succinamide salt（PA24S）was prepared by blending methanol solution of ethylene diamine（EDA）with that of succinic acid（SA）,its structure was identified through a series of advanced testing.PA24S showed fluorescent emission as solid powder and in its solution.The emission behavior of PA24S was studied with regard to concentration,excitation wavelength,pH,temperature,viscosity and nonsolvent fraction.PA24S emission was excitation and concentration dependent.It was concluded that the emission was owing to the formation of molecule clusters,and confirmed by UV-vis absorption,nuclear magnetic resonance（NMR）,transmission electron microscopy（TEM）,dynamic light scattering（DLS）and single crystal X-ray diffraction test.After that,we tested the emission of PA24S aqueous solution in presence of different metal ions,the results reavealed that Cu²⁺showed an effective quenching with good selectivity.The cytotoxicity assay demonstrated that PA24S was non-toxic to Hela cell,and suitable for cell imaging.Combined with selective quenching of Cu²⁺,PA24S was successfully used for Cu²⁺detection and monitoring.2.Poly（ethylene succinamide）,the polyamide（PA24）was prepared by solid-phase polycondensation of PA24S,its structure was characterized by FTIR,NMR,XPS,TGA,DSC,etc.The viscosity-average molecular weight of polyamide PA24 was about 1700.The absolute quantum yield of PA24 powder was 9%,and the fluorescence lifetime was 5.44 ns.PA24 solid powder and its solution in formic acid were emissive with obvious excitation dependence.These performances are all better than PA24S.In addition,PA24 can be applied to the detection of trivalent ferric ions in a solvent mixture of water-formic acid at ratio of 3/7.A linear relationship was established between the fluorescence intensity of PA24 and the concentration of Fe³⁺.