Effects of electric field and magnetic field on photoinduced dynamics and the role of molecular orientation

通过测量电场对吸收光谱和荧光光谱的影响，研究了在PMMA聚合物薄膜中由施主和受主组成的各种类型的光致电子转移过程中，外电场对电子转移过程的起始步骤、电荷复合过程和电荷解离过程的影响。场效应也已在亚甲基连接的给体-受体体系中得到验证。结果发现，电场可以提高光致电子转移的速率。电荷复合过程和电荷解离过程也受到电场的影响。此外，在含咔唑和对苯二甲酸的亚甲基化合物中，场诱导的电荷复合抑制作用明显依赖于亚甲基链长。我们还利用朗缪尔-布洛杰特技术，用一种菁染料和紫精制备了由间隔层隔开的电子供体和受体层，并在测量了电场对菁染料荧光量子产率的影响的基础上，考察了外电场对光诱导电子转移起始步骤的影响。研究发现，在外加电场的作用下，菁染料分子与紫精之间的层间电子转移受到抑制或增强，这取决于外加电场的方向。根据这些过渡物种的电致荧光光谱，研究了光化学反应产生的电子转移等分子中间体的电偶极矩和分子极化率。除了电子转移过程外，还发现其他光化学过程，如芘的准分子形成过程也受到电场的影响。

External electric firld effects on the initial step of the elctron transfer process, charge recombination process and charge dissociation process have been examined in various types of photoinduced electron transfer wtytem composed of donor and acceptor doped in a PMMA polymer film by measuring the elctric field effects on absorption and fluorescence spectra. The filed effect has been also examined in methylene-linked compounds of donor-acceptor system. As a result, the rate of the photoinduced electron transfer was found to be enhanced by an electric field. The charge recombination process as well as the charge dissociation process was also found to be affected by an electric field. In methylene-lined compounds of carbazole and terephthalic acid, further, the field-induced inhibition of the charge recombination was found to depend markedly on the methylene chain length.Electron donor and acceptor layrs separated by a spacer layr were also prepared with a cyanine dye and viologen using the Langmuir-Blodgett technique, and the effect of an external electric field on the initial step of the photoinduced electron transfer has been examined on the basis of the measurements of the field effect on the fluorescence quantum yield of the cyanine dye. Interlayr electron transfer from the photoexcited molecules of cyanine dyes to viologen was found to be deptressed or enhanced by an external electric field, depending the direction of applied electric field.Electric dipole moment and molecular polarizability of molecular intermediates produced by photochemical reaction such as an electron transfer have been evaluated from the electrofluorescence spectra of these transient species.Besides the electron transfer process, other photochemical processes, e.g., excimer formation process of pyrene, were also found to be affected by an electric field.