The Synthesis And Properties Of Functional Polyacetylene Containing Long Conjugated Chromophore

There is still a growing interest in organic compounds with large two-photon absorption (TPA) cross-section and excellent up-conversion emission properties due to their potential for application in a wide range of areas such as frequency-up-converted lasing,3-D optical data storage, lithographic micro fabrication, optical-limiting, etc. The existing organic TPA materials still have some shortages, such as low thermal stability and small TPA cross-section; the relationship between molecular structure and TPA property is still not clearly understood; there are some difficulties in synthesizing new polymer TPA materials. Therefore, it's very important to explore new TPA materials with large TPA cross-section, good comprehensive performance. Azobenzene, stilbene, fluorene and its derivatives possessing longπ-electron conjugated structure have been widely used in nonlinear optics, optical storage, light opening, optical limiting and LCD areas. In order to meeting the requirements of practical applications, stilbene, azobenzene and fluorene were used as NLO chromophores, we designed and synthesized series of conjugated polyacetylenes containing azobenzene, stilbene and fluorene NLO chromophores, respectively, and investigated the relationships between the molecular structure and TPA properties. The main contents consist of the following points:1. The principle of TPA and the testing methods of TPA cross-section and their recent development were systematically reviewed. Based on the existing problems in research and application, the contents of our research were put forward.2. A series of polyacetylene with different functional groups of azobenzene were designed and synthesized by [Rh(nbd)Cl] 2-Et3N. It was found that introduction of azobenzene chromophore pendants effectively increase the thermal stability and TPA cross-section properties of resulting polyacetylenes and endowed the polyacetylenes with novel OL properties. TPA absorption cross section (σ2) were 659, 1 220 and the 2 040 GM by using Z-scan technique, in 450 fs pulse width,780 nmwavelength. The TPA and OL properties were significantly affected by molecular structure, the polyacetylenes having strong acceptor (NO2) as a terminal group exhibites largeσ2 and well OL properties. The OL mechanism may be mainly originated from TPA of molecules.3. A series of polyacetylene with different functional groups of styrene were designed and synthesized by [Rh (nbd) Cl]2-Et3N. It was found that introduction of styrene chromophore pendants effectively increase the thermal stability and TPA cross-section properties of resulting polyacetylenes and endowed the polyacetylenes with novel OL properties. Linear dependence of solid fluorescence intensity on square of the excitation intensity confirms that fluorescence emission is originated from the TPA absorption mechanism. TPA absorption cross section (σ2) were 644,909 and the 1 140 GM by using Z-scan technique, in 450 fs pulse width,780 nm wavelength. The TPA and OL properties were significantly affected by molecular structure, the polyacetylenes having strong acceptor (NO2) as a terminal group exhibited largerσ2 and better OL properties, which is attributed to the largerπ-electron delocalization. The OL mechanism may be mainly originated from TPA of molecules.4. A series of polyacetylenes with the differentπ-electron conjugated bridge structure groups of fluorene were designed and synthesized by [Rh(nbd)Cl]2-Et3N as a catalyst. The results show that long flexible alky] chain increases the solubility and processablity of resultant polymers. It was found that introduction of fluorene chromophore pendants effectively increase the thermal stability and TPA cross-section properties of resulting polyacetylenes and endows the polyacetylenes with novel OL properties. Linear dependence of solid fluorescence intensity on square of the excitation intensity confirms that TPA is the main excitation mechanism of the intense fluorescence emission. TPA absorption cross section (σ2) were 2010 and the 3 950 GM by using Z-scan technique, in 450 fs pulse width,780 nm wavelength. The TPA and OL properties were significantly affected by molecular structure, the polyacetylenes with chromophore group of N=N double bond as conjugation bridge shows better TPA and OL performance than that with C=C asπ-conjugation bridge structure, which is attributed to the largerπ-electron delocalization. The OL mechanism may be mainly originated from TPA of molecules. 5. Based on Schweig's nonlinear theory, the second-order NLO organic chromophore can effectively enhance the third-order nonlinear optical properties of the conjugated polymer, we designed three series of conjugated poly acetylenes containing large second-order NLO chromophores (azobenzene, stilbene and fluorene) and it was expected to obtain novel polymer two-photon materials. The results show that these compounds possess good optical limiting and largeσ2, which are attributed to the long D-π-A and D-π-D conjugated electron structure of molecules, and theπ-electron conjugated bridge structure or different terminal group affects the nonlinear optical and optical limiting properties of conjugation.compounds. The study not only enriches the functionalized polyacetylene derivatives, but also provides foundation for molecular design of novel soluble polymer two-photon materials with high thermal stability.