瞬态荧光方法研究溶剂诱导的三苯胺衍生物的对称性破缺电荷转移动力学

在缺乏特征红外振动的情况下追踪具有四极或八极对称性分子的激发态对称性破缺电荷转移通常是很困难的.本文以一种具有八极对称性的三苯胺衍生物为研究对象,利用飞秒时间分辨瞬态荧光光谱方法获得发光跃迁偶极矩的演化动力学,进而实时表征了其溶剂诱导对称性破缺电荷转移的动力学过程.当该分子处于弱极性甲苯溶液中时,在激发态弛豫过程中其发射偶极矩变化较小;当处于较强极性的四氢呋喃溶液中时,其发射偶极矩在数皮秒内快速减小.在对比单体偶极分子的荧光动力学后,推断八极分子的发光态在强极性溶剂中经历溶剂诱导的结构变化,由激子耦合的八极对称性降低至激发定域的偶极对称性;而在较弱极性的溶剂中,其八极对称性在溶剂化稳定中得以较大程度的保持.     

反式-4-甲氧基偶氮苯超快激发态性质研究

本文利用飞秒瞬态吸收光谱结合量化计算研究了反式-4-甲氧基偶氮苯的超快激发态动力学和光异构过程. 瞬态光谱中在400∽480 nm波段出现永久的正吸收,表明反式分子被激发到第二激发态后最终产生了顺式结构. 在乙醇和乙二醇溶剂环境中分别获得了三个衰减组分,时间分别为0.11、1.4、2.9 ps和0.16、1.5、7.5 ps. 快速的时间组分是源自第二激发态弛豫到第一激发态的内转换过程. 另外两个组分和第一激发态的弛豫相关:一个是经第一激发态的内转化和光异构过程,另一个是顺式结构的振动冷却过程. 基于不同溶剂环境中的动力学差别,证实了光异构路径是反转机制而不是旋转机制.     

反式-4-甲氧基偶氮苯超快激发态性质研究（英文）

本文利用飞秒瞬态吸收光谱结合量化计算研究了反式-4-甲氧基偶氮苯的超快激发态动力学和光异构过程,瞬态光谱中在400～480 nm波段出现永久的正吸收,表明反式分子被激发到第二激发态后最终产生了顺式结构.在乙醇和乙二醇溶剂环境中分别获得了三个衰减组分,时间分别为0.11、1.4、2.9 ps和0.16、1.5、7.5 ps.快速的时间组分是源自第二激发态弛豫到第一激发态的内转换过程.另外两个组分和第一激发态的弛豫相关:一个是经第一激发态的内转化和光异构过程,另一个是顺式结构的振动冷却过程.基于不同溶剂环境中的动力学差别,证实了光异构路径是反转机制而不是旋转机制.     

噁嗪750激光染料分子在醇类溶剂中超快动力学研究

利用飞秒时间分辨荧光亏蚀光谱技术,研究了噁嗪750激光染料分子在典型的醇类溶剂中超快动力学过程.实验发现两个超快动力学过程:飞秒量级的快速弛豫过程和皮秒量级的慢速弛豫过程.快速弛豫过程来源于分子内振动能量再分配(IVR)和溶剂分子超快惯性弛豫动力学过程,而慢速弛豫过程对应于溶剂化的扩散分子弛豫动力学过程.实验结果表明慢速弛豫过程的时间常数随醇溶剂分子间氢键键能的增强而增大.     

采用密度泛函理论研究二甲基胺-二苯甲酮的分子内电荷转移激发态氢键

利用(含时)密度泛函理论研究了二甲基胺-二苯甲酮(DMABP)及其氢键二聚物DMABP-MeOH的光物理性质和弛豫动力学过程. 结果表明,在非极性和非质子性溶剂中,DMABP分子的第一和第二激发态跃迁同时具有局域激发和分子内电荷转移的特征;在极性质子性溶剂中,分子间氢键C=O…H-O的形成增加了这两个最低激发态之间的能量差,使DMABP-MeOH的第一激发态具有较强极性的分子内电荷转移特性. 通过计算DMABP和DMABP-MeOH分子的激发态构型弛豫势能曲线研究了激发态动力学弛豫过程. 结果表明,通过扭     

极性染料溶液的微微秒动态荧光光谱移位

本文测量了染料分子DCM、甲酚紫、DODCI和DTDCI在极性溶剂中的微微秒时间分辨荧光光谱;作者将动态的光谱移位归结为由于溶质分子激发态与基态偶极矩的显著差异而引起的周围溶剂分子的介电弛豫;并从动态的光谱移位得到的弛豫时间很接近由连续腔体理论模型求得的计算值,表明连续胜体模型用于描述动态的光谱移位现象是适用的.     

电子激发和溶剂效应对芴酮-甲醇分子间氢键增强现象的理论研究 (cited: 1)

理论研究了电子激发和溶剂效应导致的芴酮-甲醇复合体系中分子间氢键增强现象．通过基态和激发态性质的计算,不仅展示了分子间氢键键长的变化以及变化在振动光谱中的影响,而且揭示了导致氢键变化的内在物理机制：溶质分子的电子激发及溶剂化效应引起的电子重新分布,增大了溶质和溶剂分子的偶极矩,导致了它们之间的相互作用的增大,并最终加强了分子间氢键的强度．还分别对处于液相及气相中的复合体的基态和激发态的几何结构、红外谱、复合体及构成分子的偶极矩进行了理论计算,结果阐明了电子激发与溶剂化效应对氢键变化的贡献,同时还发现只有进一步引入溶剂化效应,复合体的基态、激发态的性质才能与实验达到精确一致．所有激发态均采用所开发的基于含时密度泛函理论解析计算一阶、二阶激发态能量导数的方法．     

飞秒时间分辨实验中泵浦-探测交叉相关函数的测量和时间零点的确定

飞秒激光技术的出现使得实时探测与跟踪激发态超快弛豫动力学过程成为可能,并能够给出激发态动力学过程清晰的物理图像。而在飞秒时间分辨实验中,泵浦-探测相关函数和时间零点直接影响实验结果的可靠性和准确性。本文结合飞秒激光在分子激发态超快动力学过程中的应用进展,介绍了根据实验条件和要求,在具体实验过程中泵浦-探测相关函数测量和时间零点确定的几种方法。实验中选择可见光作为泵浦光和探测光时,可以通过测定随泵浦-探测时间延迟变化的泵浦激光与探测激光的和频/差频光强来确定泵浦探测交叉相关函数和时间零点;而选择中心波长在紫外甚至真空紫外的激光脉冲作为泵浦光或探测光时,泵浦-探测交叉相关函数通常采用校正的方法测量。     

超快激光的光电应用

超快激光一般是指脉冲宽度短于10ps的脉冲激光,主要指短皮秒和飞秒(10-15s)激光。这个时间尺度短于激发态电子向晶格弛豫能量的所需时长,使光与物质相互作用呈现了与通常光激发显著不同的特性,也促成了其崭新的光电应用。围绕飞秒激光与物质相互作用快(作用时间短)、强(瞬态功率高)、精(非线性使作用区体积小,用作加工分辨率高)的特点,开展了系列研究,包括飞秒激光超快光谱用于光/电-电/光转换动力学探索,激光诱导气体成丝用于近程遥感探测,及飞秒激光微纳加工用于新原理、新材料微纳集成器件的制备。介绍了相关研究的进展。     

侧链基团对聚合物薄膜瞬态发光性能的影响

采用飞秒激光光谱技术比较研究了两种卟啉侧链聚合物:卟啉丙烯酸酯-苯乙烯共聚物P[(por)A-S]和卟啉铁(Ⅲ)丙烯酸酯-苯乙烯共聚物P[(por)FeA-S]的瞬态发光性能。并采用纳秒激光光谱技术测量了小分子卟啉(TPP)的荧光动力学过程。结果表明:P[(por)FeA-S]具有比P[(por)A-S]快得多的荧光弛豫过程,而P[(por)A-S]的荧光寿命远小于小分子卟啉的荧光寿命。对上述过程进行了分析,P[(por)A-S]的荧光衰变主要来源于聚合物分子链间的相互作用;而P[(por)FeA-S]的荧光衰变除了来源于聚合物分子链间的相互作用外,中央金属离子与配位体之间的电荷转移也对卟啉发色基团的激发态超快无辐射弛豫具有重要的影响,对上述过程的产生机理进行了讨论。     

Rotational reorientation dynamics of Rhodamine 700 in different excited states

The rotational reorientation dynamics of rhodamine 700 (LD700) in the first (S₁) and the fifth (S₅) excited state in three aprotic polar solvents have been investigated using femtosecond time-resolved stimulated emission pumping fluorescence depletion (FS TR SEP TD) spectroscopy. In both excited states, the overall rotational relaxation of LD700 occurs on a time scale of 40-230 ps depending on the solvent, and a quantitative analysis of this time constant has been performed using the Stokes-Einstein-Debye (SED) hydrodynamic theory combined with the extended charge distribution model developed by Alavi and Waldeck. The experimentally measured reorientation times for LD700 in S₅ are smaller than those in S₁, which is in accord with the predictions by the SED theory. In addition, for LD700 in S₅, a rapid initial decrease on the time scale less than 0.5 ps has been found. According to our analysis, this fast component may account for the rapid internal conversion from S₅ to S₁, and the rate of internal conversion was found to be sensitive to the solvent polarity.     

Rapid internal conversion in a symmetric molecule LD 700 studied by means of femtosecond fluorescence depletion

The rapid internal conversion dynamics at room temperature is determined by using the femtosecond time-resolved fluorescence depletion measurements of a complex solvated molecule of LD 700 (rhodamine 700) combined with steady-state absorption and fluorescence spectroscopy, as well as quantum chemical calculation. The molecule is excited by a 50fs laser pulse at 400nm which directly populated the highly excited singlet state, the rapid internal conversions (ICs) are observed, which leads to the directional changes of the emission transition moment following photoexcitation to the highly excited singlet state S₅ of LD 700.     

Diffusion of photoexcited azo dye in a liquid-crystal host

Dynamic holograms are created and studied in a D2 azo-dye-doped nematic liquid crystal. The dependence of diffraction on the excitation and probe polarizations is observed. The efficiency of excitation and the corresponding relaxation time depend also on the period and orientation of the light-interference pattern with respect to the initial molecular orientation. The excitation and diffusion of dye molecules are suggested to be the origin of these phenomena.     

Vertical-cavity surface-emitting laser in the long-wavelength (700 nm) region in the visible by energy transfer between organic dyes

In this work, organic vertical-cavity surface-emitting lasers (VCSELs) with single-mode laser output in the long-wavelength region (~700 nm) of the visible were reported based on the energy transfer between dye pairs consisting of pyrromethene 597 (PM597) and rhodamine 700 (LD700). By co-doping PM597 into the polymeric hosts, the fluorescence intensity of LD700 was enhanced by 30-fold and the photophysical parameters of the donor–acceptor pairs were investigated, indicating the involvement of non-radiative resonance energy transfer processes between PM597 and LD700. Active distributed Bragg reflectors (DBR) were made by alternately spin-coating dye-doped polyvinylcarbazole and cellulose acetate thin films as the high and low refractive index layers, respectively. By sandwiching the active layer with 2 DBR mirrors, VCSEL emission at 698.9 nm in the biological first window (650–950 nm) was observed under the 532-nm laser pulses. The laser slope efficiency and threshold were also measured.     

Linear Dichroism of Chloroplasts and Subchloroplast Fractions Oriented by Flow

Abstract

Chloroplasts as well as subchloroplast vesicles show linear dichroism (LD) when subjected to a hydrodynamic gradient. LD is positive for the ππ? in-plane polarized bands indicating that the chlorophyll porphyrin ring is in average oriented parallel1 to the elongated membrane surfaces. The vesicle fraction enriched inphotosystem I1 shows lower LD/A at 660 nm indicating lower average orientation of chlorophyll and the fraction enriched in photosystem I shows higher LD/A at 700 nm indicating that P700 is more oriented than the bulk chlorophyll.     

Near-Field and Polarized Evanescent Field Excited Fluorescence of Self-Organized Particle Arrays of Organic Dye

A wetting/dewetting process was utilized to prepare self-organized organic dye particles of micrometer and submicrometer size. Near-field scanning optical microscopy successfully identified near-field excited near-field fluorescence from single particles. The majority of the small particles with diameters around 2 mm or less, however, did not show fluorescence under near-field observation. In contrast, far-field fluorescence, when excited by a polarized evanescent field, was observed, with the intensity depending on the excitation polarization, indicating that molecules' transition moment within dye particles was oriented parallel to the substrate surface. Single particle fluorescence spectrum consistently showed an identical sharp peak with a large redshift, indicating that the particles were composed of identical dye aggregates similar to J-aggregates. These observations suggest that the near-field at the probe tip was polarized parallel to the probe axis. Another observation, that molecules were oriented in a similar direction among adjacent particles, suggests that the dewetting process contributed to the alignment of the molecular direction among adjacent particles, which further proves that the present specimen was formed by a self-organizing mechanism.     

Picosecond spectroscopy of intermolecular interactions in dye solutions

Some new experimental data on the time development of ultrashort superfluorescence (SF) in the dye solution are presented. The correlation between temporal behaviour change and the change of the spectral and spatial intensity distribution gives direct evidence of the important role of the selffocusing phenomenon in the formation of the ultrashort SF pulse synchronized with the pumping one. The oriental relaxation of solvent molecules in the dye solution not only influences the duration of the dye SF via the selffocusing mechanism but also causes a temporal change of spontaneous emission spectrum. At least two different relaxation times were found in the fluorescence spectrum of the dye in several polar solutions.     

双氰基荧光染料的合成、光学性质及其生物成像

设计合成了一种A-π-D-π-A型的双光子荧光染料3,6-双(4-乙烯基苯腈)-9-乙基咔唑,测试了其在二氯甲烷(DCM)、乙酸乙酯(EA)、乙醇(Et OH)、乙腈(ACN)、二甲亚砜(DMSO)和磷酸缓冲盐溶液(PBS)等不同溶剂中的紫外吸收光谱、单光子及双光子荧光光谱。化合物3,6-双(4-乙烯基苯腈)-9-乙基咔唑在紫外吸收光谱中存在两个相似的特征吸收带并呈现出复杂的溶剂化效应,在DMSO中具有最大荧光量子产率(86.02%),其相应的活性吸收截面为12.56 GM。在双光子荧光成像方面,染料分子具有优良的细胞膜通透性并且在双光子荧光显微镜下呈现出明亮的绿色荧光,表现出较好的双光子荧光成像性能。这些数据表明,化合物3,6-双(4-乙烯基苯腈)-9-乙基咔唑可用作一种较为理想的双光子荧光标记染料。     

Rapid wavelength scans over one octave and application to laser-induced fluorescence

Rapid excitation scans of laser-induced fluorescence (LIF) have been demonstrated. Broadband light was generated in a photonic crystal fiber and transmitted through a long fiber. Due to group-velocity dispersion in the long fiber, a wavelength scan emerged from the fiber in time. The wavelength was swept over approximately one octave in approximately 150 ns. The generated light was used to excite LD 700 Perchlorate diluted in methanol. The LIF excitation scan had a spectral resolution of approximately 15 nm, and the integrated fluorescence spectrum was found to be within 7% of the integrated absorption spectrum of the dye molecule. The method presented makes possible spatially and spectrally resolved LIF excitation scans with scanning speeds up to the limits set by the excited-state lifetime of the dye molecule.