Synthesis, Structure And Properties Of Novel Cellulose-Based Fluorescent Materials

Fluorescence polymer, as a new functional material, has its unique photophysical and photochemical properties. It has many potential applications such as fluorescent probes, chemical sensors, nonlinear optical devices, fluorescence imaging, microelectronics, and so on. Nowadays, with the strategic requirements of sustainable development, research and development of fluorescent materials based on the natural polymers has been one of the superior areas of polymer science. As the most abundant renewable resources on the earth, cellulose could be chemically or physically modified into many forms, such as films, fibers and hydrogels. Thus the functionalization and the extension of cellulose applications could be improved. So far, cellulose-based fluorescent materials are in their infancy, and how to develop novel fluorescent materials and convert cellulose into high value-added products have attracted a worldwide attention. In this thesis, we tried to prepare novel cellulose-based fluorescent materials via physical and chemical methods, and the structure, properties and their potential applications were investigated.The novel creations of this work are as follows.(1) Novel cellulose-based fluorescent materials were prepared by homogeneously etherification, surface modification, and chemical crosslinking, and their structure and properties were investigated.(2) Cellulose-based fluorescent micelles and enhanced fluorescent cellulose-based hydrogels were obtained by hydrophobic interactions and host-guest complexion, respectively.(3) The fluorescence properties of the cellulose-based fluorescent materials were investigated, and their applications in chemosensors for pH, temperature, metal ions and explosives were studied.The main content and conclusions in this thesis are divided into the following part. Firstly, carbazole-substituted hydroxyethylcelluloses (Cz-HECs) were homogeneously synthesized by reacting HEC with N-3’-bromopropyl carbazole in DMSO. The structure was characterized with element analysis, FTIR and NMR. Fluorescent properties of Cz-HECs in DMSO were syudied by a spectrofluorimeter. The results showed that the fluorescence lifetime increased with increasing DS of carbazole, and the fluorescent intensity of Cz-HECs was enhanced than that of Br-Cz. All samples exhibited concentration self-quenching properties. The addition of acrylonitrile, as an electron-accepter, quenched the emission spectra of Cz-HECs, and the fluorescence quenching was found to be a dynamic quenching by analyzing with the Stern-Volmer equation and fluorescent lifetime.Carbazole-substituted methylcelluloses (Cz-MCs) were synthesized through a two-step reaction by firstly introducing epoxy group to carbazole, and then reacting with MC. The structure was characterized by FTIR, NMR, elemental analysis and UV-vis spectroscopy. Aggregation behavior of Cz-MCs in dilute aqueous solution was investigated by a thermotropic study performed with dynamic laser light scattering. Fluorescent properties of Cz-MCs were measured by a spectrofluorimeter and results showed that Cz-MCs displayed concentration self-quenching properties of fluorescence spectra both in H2O and DMSO. The temperature effect on the fluorescent emission in dilute aqueous solution was explored. The results showed that the DS of carbazole and thermal aggregation of Cz-MC contributed to the formation of network structure between the molecules, consequently leading to the enhancement or quenching in fluorescence intensity.Fluorescein-labeled hydroxyethylcellulose (FITC-HEC) was synthesized by reacting HEC with fluorescein isothiocyanate in DMSO, and dibutyltin dilaurate was used as a catalyst. The structure was characterized by FTIR and NMR. Fluorescent properties of FITC-HEC in solution, solid state and film were investigated, and the fluorescence emission in solid state appeared an enhanced and red shift fluorescence compared to that in solution because of the formation of excimers in solid state. The effect of pH and temperature on the fluorescence intensity of FITC-HEC solution was explored. The results indicated that increasing pH could cause an increasing and then decreasing fluorescent intensity by different forms of FITC. Increasing temperature would cause a fluorescent quenching. This novel fluorescent material could be used as chemosensors for pH and temperature.Amphiphilic cationic cellulose derivatives with different long alkyl chains as hydrophobic segments (HMQC) were synthesized. They can self-assemble into cationic micelles in distilled water. Structure and properties of HMQC and micelles were characterized by element analysis, FT-IR,1H NMR, ξ-potential measurements, DLS, TEM, and fluorescence spectroscopy. The hydrophobic cores of micelles were used to load hydrophobic dye, BTPETD, to obtain fluorescent micelles which exhibiting stable photoluminescence. Fluorescence quenching was used to detect explosives, and found that the fluorescent intensity had highly sensitive respond to2,4-dinitrophenol (DNP) and picric acid (PA). It has a good linear relationship to DNP detection, while having a superlinear for c>6μM to PA, and both of them can be quantitatively detected. The limit of detection could reach to200and50nM, respectively. This novel fluorescent cellulose micelle is potential to prepare feasible, sensitive and stable sensor systems for detecting explosives in aqueous solutions.Cellulose nanocrystals were converted into pyrene labeling nanoparticles (Py-CNC) by a three-step procedure. The fluorescence emission of pyrene was enhanced after the modification to CNC. Py-CNC was evaluated for its sensing ability towards metal ions and exhibited high selectivity towards Fe3+among other screened metal ions with good discrimination between Fe2+and Fe+. The excellent selectivity for Fe+over a wide linear concentration range was observed through changes in the emission spectra. Spectroscopic analyses proved that the coordination interaction between Fe3+and Py-CNC led to the recognition process. This sensing nanomaterial can be employed as a chemosensor for Fe3+and promoted for many applications in chemical, environmental, and biological systems.β-cyclodextrin ((3-CD)/cellulose hydrogels were prepared in NaOH/urea aqueous solutions by crosslinking with epichlorohydrin. The structure and morphology of the hydrogels were characterized with FTIR, XRD, and SEM. The swelling test,5-fluorouracil (5-FU) and BSA, and aniline blue (AnB) were used to investigate the swelling capability, drug release behavior, and the fluorescent property of hydrogels. The results indicated that the swelling degree and water uptake of the hydrogels decreased with an increase of the β-CD content. The in vitro release showed an inclusion complex was formed for5-FU with β-CD to inhibit the controlled release. P-CD/cellulose hydrogels adsorbed aniline blue lead to a fluorescence enhancement attributing to the1:1host-guest complex between (3-CD and AnB.The thesis provided a new pathway for the synthesis of novel cellulose-based fluorescent materials. Meanwhile, this work has explored the potential applications in chemosensors for pH, temperature, metal ions, explosives, and so on. This thesis provided important information and scientific evidence for the preparation and utilization of cellulose-based fluorescent materials. Therefore, there are great scientific significance and prospects of applications.