【作者】 杨帆；

【导师】 孙洪波；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2010， 博士

【摘要】 本论文基于纳秒和飞秒时间分辨吸收光谱,对岩藻黄质和紫色光合细菌Thermochromatium tepidum的外周捕光天线复合物(LH2)的自由基反应机制、电子激发态性质以及激发态动力学行为进行了系统的研究,解决了其中的一些关键问题,主要成果如下:1对比研究了岩藻黄质(Fuc)在氯仿和甲醇溶液中光诱导生成自由基正离子(Fuc?+)机制的差异。结果表明在氯仿溶液中Fuc?+主要源于Fuc的单重激发态(S2),而在甲醇溶液中,则主要源于Fuc的三重激发态(T1)。2系统研究了溶剂效应对Fuc激发态性质的影响。飞秒时间分辨吸收结果揭示了在甲醇溶液中S1(2Ag?)的寿命是20 ps,而在正己烷,苯和四氢呋喃中的寿命是70 ps。S1/ICT态的能量不依赖于溶剂的极化率,然而其他的高激发态能量却依赖溶剂的极化率。3通过对DDM和LDAO两种界面活性剂制备的Tch.Tepdium的LH2复合物激发态动力学的研究,观测到由类胡萝卜素S2态介导的超快Car-to-Car和Car-to-BChl单重态能量传递过程,以及由细菌叶绿素(BChl)的Qy态介导的B800-to-B850单重态能量传递过程。发现N=11和12的类胡萝卜素分子间存在超快能量传递;N=13的类胡萝卜素在空间上与细菌叶绿素分子更加接近。4分析了LH2单体和LH2聚集体中激发态动力学行为,得到了DDM制备的LH2复合物中,LH2复合物内的B800-B850传能时间常数是1.32 ps;在水相中LH2聚集的情况下,由于存在复合物间存在聚集,因此B800-B850这一传能时间常数变为1.10 ps和0.9 ps。B850的各向异性动力学结果揭示了21 ps的LH2复合物间的能量传递过程。更多还原

【Abstract】 As the most abundant naturally occurring carotenoid(Car), fucoxanthin(Fuc) has a carbonyl group conjugated to its polyene backbone, and, therefore, bears rather unique excited-state properties. On the other hand, the light-harvesting complex 2 (LH2) from the thermophilic photosynthetic purple bacteria Thermochromatium (Tch.) tepidum has heterogeneous polypeptide and Car compositions, and the detailed structural information are unavailable yet. This thesis is intended to study, by the use of ultrafast time-resolved spectroscopies, the excited-state properties and the free radical reaction mechanism of fucoxanthin, as well as the excitation energy transfer dynamics of both isolated and aggregated LH2 complexes. The results are helpful in understanding the structure-function relationship of the aforementioned photosynthetic Car and antenna complex.1. Photoinduced formation Fuc radical cation in organic solventsThe formation of Fuc radical cation (Fuc?+) in chloroform and in methanol was comparatively investigated by means of nanosecond time-resolved absorption spectroscopy combined with spetroelectrochemistry. By comparing the mechanisms of Fuc?+ generation under direct photoexcitation and anthracene-sensitized triplet excitation, it was concluded that in chloroform Fuc?+ was mainly derived from the second lowest singlet excited state of Fuc (S2), whereas in methanol mainly from the lowest triplet excited state (T1). The results are helpful in understanding the antioxidation or photoprotecting roles of Fuc in complex micro-environment.2. Solvent effect on the low-lying singlet excited states of FucThe excited state properties of the Fuc in methanol, n-hexane, tetrahydrofuran and benzene were examined, respectively, by means of steady-state and femtosecond time-resolved spectroscopies. The complete spectra of broad-band fluorescence spectra covering 600~1100 nm were recorded, which were ascribed to the S1/ICT state emission. In non-hydrogen bond solvent the state energy and lifetime of the S1/ICT state are independent on the solvent polarizability, however, those of other higher-lying excited states are dependent. In hydrogen bond solvent the S1/ICT state lifetime depends linearly on solvent polarizability, whereas the excited state energy deviates from linear dependence, indicating the prominent conformational change of Fuc molecule.3. Excitation Dynamics of LH2 from Tch. tepidumWe have examined, by means of femtosecond time-resolved absorption and dynamic Stark spectroscopy, the Car-to-Car excitation energy transfer(EET) among Cars of different conjugated lengths (N), the Car-to-bacteriochlorophyll(BChl) EET and the BChl-to-BChl EET processes of isolated LH2 complex prepared with different surfactants. These ultrafast processes suggest that the Cars with N=11 and 12 coexistence in a LH2 complex and the Car with N=13 locates in closer proximity to BChl with reference to other Cars. In addition, the B800-to-B850 molecular orientation is proposed to differ considerably from that of other extensively investigated bacterial species. Importantly, Cars with N=12 as a minor Car composition is found to be an efficient trap of excitation energy, which may contribute to the photoprotection of the LH2.4. Effect of Aggregation on the Excitation Dynamics of Solubilized and Chromatophore-Embedded LH2 complexes of Tch. tepidumInfluence of detergent concentration on the aggregation of LH2, and the intra- and inter-complex excitation dynamics of solubilized and chromatophore-embedded LH2 complexes were investigated. The intra-LH2 EET dynamics, i.e. B800→B800, B800→B850 and B850→B850, as well as the inter-complex EET dynamics, i.e. LH2→LH2, LH2→LH1and LH1→RC, were examined. The intra-LH2 B800→B850 energy transfer time for mono-dispersed LH2 was determined to be～1.32 ps, and the inter-complex LH2(B850)→LH1(B915) transfer time was found to be 6.62 ps, both of which are considerably longer than the values documented for other bacterial species. Furthermore, the depolarization of B850* excitation among LH2s showed a decay time constant of 21 ps, which corresponds to a free path of spatial migration of 30~40 nm (3~4 LH2s). The results are helpful in understanding the roles of LH2 clustering in native photosynthetic membrane.更多还原