Synthesis And Layer-by-Layer Assembly Of Dendrimers Bearing Fluorescent Cores

Dendrimers are novel polymer materials, which were successfully synthesized in the recent twenty years. Dendrimers perfectly combine the properties of linear macromolecules with high molecular weight and small molecules with well-defined molecular structure. Unique properties of dendrimers, such as the uniform size, stable 3-dimensional structure, the easily functionalized peripheral groups, tunable solubility and the large amount of peripheral functional groups make them ideal molecular building blocks for a wide range of interfacial assemblies. By introducing monofunctional or multifunctional small molecules into the core or the periphery of dendrimers, chemists can create a large number of functional dendrimers. Moreover, the multifunctional dendrimers would remarkably enrich the interface science and film-materials science if they were introduced into the ultrathin films. In the research field of films, LB films, self-assembly monolayers and Layer-by-Layer assembly multilayer films were extensively studied. The thickness of an individual layer can range from several nanometers to several angstroms, which makes it easy to manipulate the structures and functions of films within the limited space in the direction of film growth. The ultrathin films fabricated by the existing assembly methods can be either multilayer or monolayer. The amounts and types of materials on the multilayer films significantly increase in comparison to those on the monolayer films, which will enrich the functionality and realize the function-integration of the ultrathin films. Chapter â… of this thesis is the introduction, which includes some basic concepts of dendrimers, typical properties of the dendrimers with versatile functional cores, the existing assembly techniques for layered film construction and some progress in the field of interfacial assembly of dendrimers. In chapter â…¡, by using the one-generation and two-generation dendrimers with diphenylanthracene cores as building blocks, we prepared single-component luminescent films with precisely controlled film thickness. The fluorescence quenching of the chromophores in the ultrathin film reduced and the fluorescence emission intensity of the film was enhanced. First, we synthesized one-generation and two-generation poly(benzyl ether) dendrons bromides using convergent method. Then coupling reactions of 9,10-Bis(3,5-Dihydroxyphenyl)anthracene(An) and dendron bromides were performed. After the hydrolysis reaction, one-generation and two-generation poly(benzyl ether) dendrimers with diphenylanthracene cores and carboxyl peripheral groups were synthesized. We measured the UV-Vis spectra and fluorescence spectra of the two dendrimers in solution. Then single-component films of the two dendrimers were prepared by the self-deposition method. UV-Vis absorption spectroscopy was used to monitor the fabrication process of the thin films. It was found that bothtwo-generation dendrimers and one-generation dendrimers could form self-deposition film. We prepared the self-deposition films of one-generation and two-generation dendrimers with approximately equal absorbance in the range of the characteristic absorption of a diphenylanthracene core. It was found that the fluorescence emission intensity of the two-generation dendrimer film is 2.4 times as high as that of the one-generation dendrimer film. We believed that the increase of generation of dendrimer decreased the density of the diphenylanthracene core in the film, which effectively reduced the quenching of the chromophores. The red shift of the maximum fluorescence emission (the difference between the maximum fluorescence emission obtained from the self-deposition film and that from the solution) of the two-generation dendrimer is smaller than that of one-generation dendrimer, which further indicated that high-generation dendrimer has a stronger site-isolation effect on the core than low-generation one. Moreover, We also attempted to prepare single-component thin films of the two dendrimers using spin coating and simple casting methods and found it was difficult to obtain a nanoscale thickness-controlled dendrimers thin solid films. Therefore the Use of the self-deposition method to construct single-component luminescent film is very meaningful because we can not only precisely control the thickness of the single-component film but also enhance the fluorescence intensity of the ultrathin film. In chapter â…¢, we studied the effect of the number of carboxyl groups on the construction of hydrogen-bonding-directed dendrimers/poly(4-vinylpyridine) multilayer films since there are different numbers of the carboxyl groups at the periphery of one-generation and two-generationdendrimers. We used the one-generation and two-generation dendrimers with diphenylanthracene cores to conduct alternating deposition with poly(4-vinylpyridine)(PVPy) in methanol solution. As for the two-generation dendrimer containing sixteen carboxyl groups, it was found that UV-Vis absorbance of the film increased not only after immersing in the solution of dendrimer but also after immersing in the solution of PVPy. For the one-generation dendrimer containing eight carboxyl groups, the UV-Vis absorbance only increased after immersing in the solution of dendrimer and almost did not increased after immersing in the solution of PVPy. These phenomena showed that an obvious amount of PVPy deposition occurred in the two-generation dendrimer/PVPy multilayer film, but a little amount of PVPy deposition in the one-generation dendrimer/PVPy multilayer film. The FT-IR spectroscopy was used to study the composition of the above films and consistent results were obtained with that of UV-Vis spectroscopy. Because the deposition conditions of the two films are definitely the same, we inferred that the number of carboxyl groups at the peripheries of the two dendrimers affected the deposition of PVPy. To further verity our conjecture, we conducted the film preparation in the mixed solvent with relative weak polarity. It was found that the amount of PVPy deposited in the one-generation dendrimer/PVPy multilayer film obviously increased. Increasing the molecular weight of PVPy, we also increased the deposition amount of PVPy. The two experimental phenomena provide supporting results for our conjecture. In chapter â…£, using two dendrimers bearing diphenylanthracene core and tetraphenylporphyrine core with the same exterior structure and similarsize as the building blocks, we fabricated multicomponent thin film with precisely controlled composition. Through simply changing the molar ratio of dendrimers in solution, we successfully realized the control of composition in the multilayer films containing dendrimers. First, we synthesized the two-generation dendrimer with the tetraphenylporphyrine core and carboxyl peripheral groups. We used the tetraphenylporphyrine core and diphenylanthracene core poly(benzyl ether) dendrimers with sixteen carboxyl groups at the periphery to alternately deposit with PVPy, respectively. Through UV-Vis spectroscopy, we found that the two dendrimers had similar surface molar density in the alternating deposition film. This result meant that the two dendrimers had the similar deposition amount per deposition cycle. FT-IR spectroscopy indicated that the driving force for the film construction of these two dendrimers is the same and is based on hydrogen bonding interaction between carboxyl groups of dendrimers and pyridyl groups of PVPy. Changing the ratio of the two dendrimers and keeping the concentration constant, we prepared mixed solutions of the two dendrimers with nine ratios. Using PVPy solution and the mixed solutions of the two dendrimers, we prepared multicomponent alternating deposition films of the two dendrimers. It was found that the ratio of the porphyrine core dendrimer in the multicomponent film increased with the increase of the porphyrine core dendrimer in the solution. Through "linear combination", we obtained the ratio of the two dendrimers as well as their total surface molar density in the multicomponent film. It was found that the total surface molar density of dendrimers was independent of the ratio of the two dendrimers in solution. The ratios of the two dendrimer in the alternating multilayer films were...