Study On The Synthesis And Properties Of Fluorene-based Two-photon Absorption Functional Materials

Two-photon absorption has attracted great interest of researchers owing to their obvious advantages over conventional one-photon absorption in many fields, which has led to extensive applications in microscopy, microfabrication, three-dimensional data storage, optical power limiting, upconverted lasing, photodynamic therapy, and for the localized release of bio-active species. Fluorene derivatives are the most widely studied two-photon absorption materials because of their large electron delocalization, high photoluminescence quantum yield, and good thermal and chemical stabilities. However, the existing two-photon absorption materials still have some shortages, such as:low thermal stability and small two-photon absorption cross-section, in particular, and incomplete understanding relationship between molecular structure and property. To improve the practical applications and obtain two-photon absorption materials with large two-photon absorption cross-section, we designed and synthesized a series of conjugated polyacetylenes and polyhedral oligomeric silsesquioxane (POSS)-based organic/inorganic hybrid nanocomposite materials containing fluorene-based chromophores by connecting the chromophore to the polyacetylene main chain or nano-sized inorganic POSS core, and investigated the relationships between the molecular structure and two-photon absorption and optical limiting properties of the materials. The main contents of this dissertation are consisted of the following points:1. The essential theory of two-photon absorption and the testing methods of two photon absorption cross-sections were reviewed briefly. The structure-property correlations of materials were highlighted and the wide range of potential applications was systematically reviewed.2. We designed and synthesized four symmetrical fluorene derivatives with the large D-Ï€-D or A-Ï€-A conjugated systems, tested their properties of linear optics, two photon absorption and optical limiting, and studied systematically the relationship between molecular structure and property. It was found that the molecular structure and solvent effect obviously influenced the linear absorption and fluorescent properties of the compounds. UV-vis and fluorescence spectra were red-shifted by the increase of conjugated systems and polarity of solvent. The fluorescence intensity of compound with the strong acceptor (NO2) was reduced because of fluorescent quenching, and the compound had the most obvious red-shifted phenomenon. Two photon absorption properties of the four symmetrical fluorene derivatives were also affected by the molecular structure. The compound with the strong acceptor (NO2) showed the largest two photon absorption cross-sections. Simultaneously, compound with long alkyl flexible chain showed better solubility than that with short one, but their optical properties were little affected by the length of alkyl flexible chain. It was also found that four compounds showed the good optical limiting properties under the two testing conditions (fs and ps pulse) and the optical limiting mechanism under ps pulse may mainly originate from two photon absorption of molecules.3. Considering the structural characteristics of polyacetylenes and POSS, we designed and synthesized four fluorene-containing terminal acetylene monomers. Their molecular structures were characterized by FTIR,1H NMR and 13C NMR. The linear optical and two absorption properties were tested in detail. It was found that the four terminal acetylene monomers have the high two photon absorption cross-sections, and the values were also influenced by the molecular structure, which is same as the result of four symmetrical fluorene derivatives abovementioned.4. Using [Rh(nbd)Cl]2 as a catalyst, a series of functionalized polyacetylenes with the fluorene-based chromophore pendants were synthesized by varying the length of alkyl flexible chain, the structure of terminal group and the property of donor or acceptor. The influences of the molecular structure on the two photon absorption and optical limiting properties were investigated systematically. It was found that introduction of fluorene-based chromophore pendants effectively increased the thermal stability of polyacetylenes, and endowed the polyacetylenes with novel two photon absorption and optical limiting properties. The two photon absorption and optical limiting properties were significantly affected by molecular structure. Polymer with strong acceptor (NO2) as a terminal group exhibited larger two photon absorption cross-sections and better optical properties. Simultaneously, it was also found that polymer with long alkyl flexible chain directly showed better solubility than that with short one, but their two photon absorption and optical limiting properties were little affected by the length of alkyl flexible chain. The studies pave a new direction and provide a new way for design and preparation of new two photon absorption materials.5. Using Pt (dcp) as a catalyst, a series of POSS-based organic/inorganic hybrid nanocomposite materials were designed and synthesized by the hydrosilylation, which were linked the fluorene-based chromophore by the covalent bond. The results showed that the incorporation of POSS effectively restrained the aggregation effect of organic luminescent chromophores and enhanced the photoluminescence quantum efficiency of hybrid. It was also found that incorporation POSS core into the fluorene-based chromophores could obviously promote the thermal stability of the hybrid materials. Furthermore, the hybrid materials were endowed the novel two photon absorption and optical limiting properties. The properties were affected by the solubility and steric blockage of the fluorene-based chromophores. The nanocomposite with the terminal group of strong acceptor (NO2) showed not perfect two photon absorption property because of poor solubility. In addition, the hybrid with long alkyl flexible chain showed better solubility than that with short one, but possessed small two photon absorption cross-sections, which was mainly originated from low number of chromophore incorporated into POSS due to the strong steric blockage of long alkyl flexible chain. The works supply the foundations for the design of new two photon absorption materials.