量子点/有机分子界面光致电荷转移过程中电子激发态振动结构的飞秒时间分辨瞬态光栅受激发射光谱研究

The molecular excited states structure and restructuring energy have an inportant influence in the efficiency and paths of photoinduced charge transfer. The changes of molecular Excited states structure usually happen in the time scale from 10 fs to 1 ps. Super fast time-resolved vibration spectra technology such as coherent anti-Stokes Raman scattering (CARS), femtosecond stimulated Raman spectroscopy (FSRS) and femtosecond impulsive Ranman spectroscopy (FIRS) have been developed to detect the change of the electronic excited states vibration. The drawback of the present spectra technology is low signal-to-noise ratio. It is also difficult to distinguish excited states molecules from ground state molecules. A new femtosecond time-resolved transient grating stimulated emission spectroscopy (TGSES) is established based on time-resolved transient grating technology and electronic excited states stimulated emission theory. TGSES can directly track the evolutionary process of electronic excited states vibration with high time resolution (100 fs) and spectral resolution (10 wave number). The dynamics of photoinduced charge separation and the motion of the resulting electrons are examined in the composite material of quantum dots and typical organic molecules (such as MEH-PPV, porphyrins). The charge migration transfer paths can be be obtained by analysing the electronic stimulated emission in the TGSES. The efficiency of photoinduced charge transfer may be markedlly increased if the phase separation of the electron donor and acceptor materials can be controlled to eliminate interfacial boundaried along the charge transfer paths.

激发态分子结构以及相应的重组能是影响光致电荷转移效率和途径的关键因素。 激发态分子结构的变化通常发生在10fs到1ps的时间尺度内，追踪分子电子激发态 振动结构的变化过程，需要高的时间分辨和光谱分辨技术手段。现有用于探测激发态分子结构的超快时间分辨振动光谱技术都存在信噪比低，而且难于区分基态分子和激发态分子的缺陷。本项目基于时间分辨瞬态光栅技术和分子电子激发态的受激发射光谱理论，建立一种新的飞秒时间分辨瞬态光栅受激发射光谱实验技术，能够直接追踪电子激发态振动结构的演化过程，时间分辨率优于100飞秒，光谱分辨率可达到10波数。通过监测量子点与典型的有机分子（如MEH-PPV、卟啉）间光致电荷转移过程中的电子激发态振动能级的受激发射，追踪有机分子经Frank-Condon 跃迁后，激发态分子结构的演化过程，获得无机量子点与有机分子间光致电荷转移的路径信息,从而找到提高电荷转移效率的方法。

基于时间分辨瞬态光栅技术和分子电子激发态的受激发射光谱理论，建立一种新的飞秒时间分辨瞬态光栅受激发射光谱实验技术，能够直接追踪电子激发态振动结构的演化过程，时间分辨率优于100飞秒，光谱分辨率可达到10波数。 推导了自发拉曼散射强度、受激拉曼散射强度与相干反斯托克斯拉曼散射强度的温度依赖性公式，给出了相关的理论分析，并且获得了新的受激拉曼散射强度的温度依赖性公式。搭建飞秒时间分辨瞬态光栅系统，完成了受激拉曼散射的温度依赖性实验，结果表明该方法可以测量出温度的变化趋势，从而反映出分子间的能量转移过程。在氯仿溶液中，获得了不同尺寸CdSe量子点与不同浓度聚苯胺的复合体，实验发现量子点尺寸减小和聚苯胺浓度增加时复合体荧光强度会降低。研究表明，一方面是由于CdSe量子点向聚苯胺的共振能量传递，另一方面是由于聚苯胺可以有效截获CdSe量子点中的电荷传递，两者共同导致复合体的荧光淬灭现象。采用连续离子层的吸附和反应的制备方法，制备不同层PbS/TiO2复合结构构筑太阳能电池，分析不同层数光阳极对量子点敏化太阳能电池光电转换效率的影响。