Investigations On The Application Of Carbosiloxane Dendrimer In Organic Dye And Nanocrystals

Since 1967 when dye laser was developed, the investigations on the properties and applications of laser dye have gained increasing attention. Up to date, however, it is still difficult to increase the fluorescence efficiency of laser dye via preventing its self-aggregation and self-quenching. Dendrimer is a kind of high-branched materials with repeated units and regular morphologies, which brings excellent monodispersity. Therefore, it is hopeful to apply dendrimer as host material into dye system to prevent the interactions between the dye molecules. Furthermore, dendrimer can act as a stabilizer to induce the formation of organic nanocrystals. In this thesis, we focus on the issues of doping carbosiloxane dendrimer into laser dye system to improve the luminescent properties and utilizing the dendrimer aggregation to tune the formation of organic nanocrystals as well as investigating the optical properties of nanocrystals.The thesis consists of six chapters and the main point of each chapter is shown as follows:Chapter 1. This chapter covers literatures review. Concepts, properties and applications of dendrimers as host materials in host-guest chemistry and dendrimer aggregation are discussed. The key problems in improving the fluorescence efficiency of laser dyes and obtaining the stable organic nanocrystals were summarized. Finally, we illustrated the purpose and the significance of our research in this thesis.Chapter 2. To achieve our research purpose, we designed and synthesized different generations of the carbosiloxane dendrimer. Moreover, we confirmed the structures by 1HNMR and IR. This chapter provides the chemical material for the further studies. Chapter 3. In this section, we provided the method of achieving optical enhancement by using carbosiloxane dendrimer to dope Rhodamine B (RhB). As expected, the self-aggregation and self-quenching of RhB molecules were avoided. Furthermore, we studied the optical properties by investigating the fluorescence and laser emission of this host-guest system. The improved fluorescence efficiency, lower laser threshold and higher conversion efficiency were achieved. Carbosiloxane dendrimer shows excellent site-isolation for dye molecules. The study here offers a novel method to obtain optical enhancement and provides a new research orientation for investigating optical functional materials.Chapter 4. Dendrimer could aggregate while the environment around it changes. Herein, we utilize the change of UV-Vis absorption spectra caused by the isomerization equilibrium of RhB molecule to confirm the formation of dendrimer aggregation and the critical aggregation concentration (CAC). Furthermore, the results from the Gibbs energy and electrolytic conductivity provided further evidence for confirming the CAC of dendrimer in dilute solution and showed good agreement with UV-Vis absorption result. The proposed method is not only effective in estimating the CAC of dendrimer in dilute solution, but also promotes the investigation of tuned organic nanocrystals with dendrimer in Chapter 5.Chapter 5. Based on the studies in last section, we intensively investigated the effect of carbosiloxane dendrimer aggregation in the growth process of organic nanocrystals. Besides, we evaluated the optical properties, such as one-photon fluorescence, two-photon fluorescence, two-photon absorption cross section and lifetime of size-controlled nanocrystals. All the investigation showed that carbosiloxane dendrimer played an important role in tuning and stabilizing the formation of organic nanocrystals. Moreover, the size-controlled organic nanocrystals showed extraordinary optical properties.Chapter 6. We summarized our study and proposed the future prospect.