新型多环芳烃分子中的超快光学非线性及其光限幅应用

发布时间：2018-04-22 17:02

本文选题：多环芳烃 + 瞬态吸收光谱　；参考：《哈尔滨工业大学》2017年博士论文

【摘要】：多环芳烃类分子由于其优秀的电荷输运、荧光性能在场效应管、有机发光二极管等应用中有着巨大的潜力。与之相比,多环芳烃分子的平面π共轭体系在非线性光学上却鲜有系统性的研究。本论文中,我们对基于多环芳烃分子的一系列材料的超快光学非线性进行研究。依托可调谐的飞秒光源和皮秒、纳秒激光,使用时间分辨的光谱技术分析了一系列多环芳烃类分子结构的光学非线性机制。结合数值模拟与理论计算,对分子结构与光学非线性响应之间的结构-性质关系进行了讨论。研究工作包括以下几个方面:以一种扭转平面多环芳烃分子中观测到的长寿命宽带单重态吸收为基础,设计并合成一组直线型对称结构、中心使用π电子桥的多环芳烃分子。在保留宽带单重态吸收的前提下大幅增强双光子吸收,实现了基于单重态的双光子诱导宽带激发态吸收。改善了以往三重态吸收材料响应速度慢的缺点,实现了响应飞秒、皮秒、纳秒脉冲的超快宽带反饱和吸收。利用双光子诱导宽带单重态吸收中响应时间快的优势,基于线型对称结构的多环芳烃分子,开发一种在飞秒、皮秒脉冲下具有优秀性能的宽带光限幅材料。实验结果显示该新型材料具有宽带、高透过、限幅强三大优势,且其中的任一项都超过绝大多数已知的光限幅材料。作为对比,测试了分支型结构分子的光限幅响应,通过分子前线轨道计算分析分支型结构光限幅效应弱于直线型结构的原因。在上述工作的基础上,在分子结构中引入强电荷受体,通过与没有受体的情况对比,研究分子内电荷转移过程对直线型对称结构多环芳烃中光学非线性响应的影响。通过Z扫描,瞬态吸收和折射等研究手段,结合理论计算讨论分子电荷转移过程对非线性吸收与折射的影响。在了解多环芳烃分子内电荷转移对光学非线性响应的基础上,设计并合成一组不对称结构的芘类衍生物分子。通过电荷给受体之间的分子结构扭转,在减弱非线性吸收的同时增强非线性折射。多波长的Z扫描实验结果显示该分子在600 nm~1030 nm内具有大于1的品质因数,证明是一种优秀的宽带非线性折射材料,在全光开关的应用领域有巨大的潜力。通过瞬态折射手段分析了共振与非共振机制下分子的非线性折射机制,为将来材料的进一步优化提供参考。
[Abstract]:Polycyclic aromatic hydrocarbons (PAHs) have great potential in applications such as field effect transistors (FET) and organic light emitting diodes (OLEDs) due to their excellent charge transport fluorescence properties. In contrast, the planar 蟺-conjugated systems of polycyclic aromatic molecules are rarely systematically studied in nonlinear optics. In this thesis, we study the ultrafast optical nonlinearity of a series of materials based on polycyclic aromatic hydrocarbons (PAHs). Based on tunable femtosecond light source, picosecond laser and nanosecond laser, the optical nonlinear mechanism of a series of polycyclic aromatic hydrocarbons (PAHs) molecular structures was analyzed by time-resolved spectroscopy. The structure-property relationship between molecular structure and optical nonlinear response is discussed in combination with numerical simulation and theoretical calculation. The research work includes the following aspects: based on the long-lived broadband single state absorption observed in a torsional plane polycyclic aromatic hydrocarbons (PAHs), a set of linear symmetric structures with 蟺 electron bridge are designed and synthesized. The two-photon absorption is greatly enhanced while retaining the broadband single state absorption, and the two-photon induced broadband excited state absorption is realized based on the single state. It improves the shortcoming of the slow response speed of the triplet absorbing materials in the past, and realizes the ultra-fast broadband reverse saturation absorption of femtosecond, picosecond and nanosecond pulses. Based on linear symmetric polycyclic aromatic hydrocarbons (PAHs), a wide band optical limiting material with excellent performance under femtosecond and picosecond pulses was developed based on the advantage of fast response time in two-photon induced wideband single state absorption. The experimental results show that the new material has three advantages: wide band, high transmission and limiting strength, and any one of them exceeds most known optical limiting materials. As a contrast, the optical limiting response of branched structure molecules is measured. The reason that the optical limiting effect of branched structure is weaker than that of linear structure is analyzed by molecular frontier orbital calculation. On the basis of the above work, the strong charge receptors are introduced into the molecular structure. By comparing with those without the receptors, the influence of intramolecular charge transfer process on the optical nonlinear response in linear symmetric polycyclic aromatic hydrocarbons is studied. The influence of molecular charge transfer process on nonlinear absorption and refraction is discussed by means of Z scan, transient absorption and refraction. Based on the understanding of the optical nonlinear response of intramolecular charge transfer of polycyclic aromatic hydrocarbons (PAHs), a group of asymmetric pyrene derivatives were designed and synthesized. By torsion of the molecular structure between the receptors, the nonlinear absorption is weakened and the nonlinear refraction is enhanced. The results of multi-wavelength Z-scan experiments show that the molecule has a quality factor of more than 1 at 600 nm~1030 nm. It is proved to be an excellent broadband nonlinear refractive material and has great potential in all optical switching applications. The nonlinear refraction mechanism of molecules under resonant and non-resonant mechanisms is analyzed by transient refraction, which provides a reference for the further optimization of materials in the future.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O625.15

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