| Since organic molecular structures are of diversity and can be easily modified, specifically functional materials with certain properties can be designed and synthesized according to some practical demands. PPV and its derivatives possess delocalized conjugatedπ-electron and can be doped with many materials, and their structures can be readily cut out, accordingly, their properties can be optimized by modifying the backbone or the length of the side chain. Porphyrins, phthalocyanines and their derivatives also are promising nonlinear materials. Their molecules with two dimensional planar structures have strongπ-electron conjugated systems, and their structures also can be modified, such as the out rings can be substituted freely, central metals can be changed, the size of the ring can be expanded etc.. Because of their large nonlinear coefficients, fast optical response rates, high laser damaging threshold values, good chemical and thermal stability, suitability to mass production due to low prices of raw materials etc., the three kinds of materials have a great deal of potential applications in fast optical switches, optical storages, optical limiters, transducers, optical communications and organic luminescence etc.. Therefore, probing structural characters of these conjugatedπ-electron systems and investigating their linear and nonlinear optical properties are significant not only for synthesizing more valuable materials but also for practical applications.The principal work in this paper is to investigate the linear and nonlinear optical properties of the three kinds ofπ-electron conjugated materials by UV-VIS-NIR spectroscopy, fluorescence spectroscopy and picosecond Z-scan technique with 532 nm and 1064 nm excitation. The optical properties of these samples were discussed using the theories ofπ-electron conjugated structures and resonant/non-resonant enhancement respectively, which will help us to further understand their nonlinear optical characters. This paper is divided into five chapters, which can be summarized as below.In the first chapter, the research background and the current status of the development and practical applications of nonlinear optics are briefly introduced. The third-order nonlinear optical effects of organic materials are introduced particularly. The theory and the method of Z-scan technique for measurement of nonlinear optical coefficients are described in detail. In addition, the mechanism and the development of optical limiting effect are also presented.In the second chapter, the effect of side chains on the optical properties of two PPV derivatives, MEH-PPV and DO-PPV, have been investigated detailedly. Their optical properties were discussed using the theories ofπ-electron conjugated structures and resonant/non-resonant enhancement, respectively. The obtained results demonstrated that the absorption and PL emission bands of PPV shift towards lower photon energy, indicating the energy gap of PPV derivative decreases with the increasing of PPV side-chain length. Furthermore, the side chains of PPV derivatives also affects the third-order nonlinear susceptibilitiesχ3 of PPV polymers. Under the resonant excitation, the third-order nonlinear susceptibilityχ3 of MEH-PPV at 532 nm showed a maximum, 9.30×10-10 esu, which is two-order of magnitude larger than that of DO-PPV.In the third chapter, the linear and nonlinear optical properties of three porphyrin compounds with different substituents, T(4-HP)P, T(4-EP)P and T(4-BrP)P, have been studied detailedly. The obtained results showed that the absorption and PL emission bands of T(4-HP)P substituted by stronger donating electron group shifted towards lower photon energy compared with T(4-EP)P substituted by weaker donating electron group and T(4-BrP)P substituted by withdrawing electron group; All the three compounds had positive third-order nonlinear susceptibilities, and with stronger donating electron group and the excitation wavelength at 532 nm close to the resonance field, the third-order nonlinear susceptibilityχ3 of T(4-HP)P showed a maximum value, 6.81×10-10 esu, which is two-order of magnitude larger than that of T(4-BrP)P. Simultaneously, the reverse saturated absorption at 532 nm and the two-photon absorption at 1064 nm were observed. On the base of two-photon absorption, the optical limiting properties were studied, whose results indicated that the optical limiting effect of samples was very good.In the fourth chapter, the third-order nonlinear optical properties and the optical limiting effect of two kinds of metallophthalocyanines with different central ions, p-HPcCo and p-HPcZn, have been investigated mainly by picosecond pulsed laser. The results of Z-scan experiment indicated that both the two metallophthalocyanines had positive third-order nonlinear susceptibilities, and with stronger withdrawing electron ion and the excitation wavelength at 532 nm close to the resonance field, the third-order nonlinear susceptibilityχ3 of p-HPcZn showed a maximum value, 1.76×10-10 esu, which is almost two-order of magnitude larger than that of p-HPcCo. Simultaneously, the reverse saturated absorption at 532 nm and the two-photon absorption at 1064 nm were observed. The optical limiting experiment results showed that the two different mechanisms, two-photon absorption and nonlinear refraction, determined their optical limiting properties together.In the fifth chapter, the discussions and conclusions are made for the whole paper, and the assumption for next work is put forward.
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