Preparation And Luminescence Properties Research Of Nitrogen-Containing Lfuorescent Organic Compounds

Recently, much attention has been focused on the fluorescence phenomenon ofnitrogen-containing organic compounds without fluorophores. Further investigationson the issue are of great theoretical and practical significance. However, researcheson this topic are at an initial stage, therefore, crucial matters such asphotoluminescence mechanism and influencing factors are still outstanding. Herein,we reported three kinds of typical systems of nitrogen-containing organic compounds,i.e., small molecular amine, hyperbranched poly(amido amine)s and poly(amidoamine) dendrimers, in addition, the effects of pH value, molecular weight, molecularstructure and oxidation on fluorescence were characterized comparatively in order tolay a foundation for further explanation of the photoluminescence mechanism.Poly(amido amine) dendrimers were prepared by divergent method, it is showedthat fluorescence intensity of poly(amido amine) dendrimers with the same terminalenhanced in company with the increase of generation, and the pH value plays animportant role in the fluorescence properties. The pKa of nitrogen-containing groupsis close to the pH value where the maximum fluorescence occurs, indicating that theremight be some connections between them. Poly(amido amine) dendrimers oxidizedby ozone and hydrogen peroxide were put forward for the first time to promote thegeneration of fluorescence. These two oxidants show excellent properties on theformulation of fluorophores, fluorescence intensity, and minimization of theenvironmental pollution.One-pot method was used to produce hyperbranched poly(amido amine)s, and acouple of fluorescence emission peaks were observed at370and450nm respectively.The370nm peak was detected for the first time, but transited to450nm after athermal treatment. We speculated that might come from an unstable structure of thehyperbranched poly(amido amine)s. Simultaneously, we found that the fluorescenceintensity enhanced along with the increasing of molecular weight, indicating thatmolecular weight is a momentous factor as well as the oxidation and acidity. On theother hand, on account of the simple steps and low costs, hyperbranched poly(amido amine)s prepared by using one-pot method has much more applications compared topoly(amido amine) dendrimers. White fluorescence can be observed after the mixtureof hyperbranched poly(amido amine)s and Rhodamine B (RhB), make it possible toapply on the exploitation of novel fluorescence materials.Fluorescence properties of1,2-Ethylenediamine was studied in order to furtherinvestigate the nitrogen-containing fluorescence system and obtains much moreinformation. Small molecular weight and simple structure of1,2-Ethylenediaminemake it possible to be characterized by using Fourier transform infrared (FT-IR)spectroscopy and Nuclear magnetic resonance (NMR) spectroscopy, which couldmake up for the defects of compounds, such as hyperbranched poly(amido amine)s,whose structure could not be determined, All of these features make it useful onstudying of photoluminescence mechanism. In addition, fluorescence peaks similar tooxidated poly(amido amine) dendrimers can be observed after the oxidation of1,2-Ethylenediamine, despite the weak fluorescence intensity, there is a samefluorophore.Special performance was found during the experiment process. The fluorescenceintensity was weakened gradually under the continuous irradiation of exciting light,and recovered to some extent after standing for a period of time. Moreover, cottonfiber ingrained by those three nitrogen-containing fluorescence organic compoundscould emit bright fluorescence under the UV light, this might provide basis for theirapplication to fluorescence labeling.