RESEARCH ON THE PRIMARY PROCESSES OF PHOTO-CONDUCTION IN AROMATIC VINYL POLYMERS BY MEANS OF FEMTOSECOND DICHROISM MEASUREMENT AND NEAR LASER SPECTROSCOPY.

光激发引发的电子输运在自然界和人工系统中都是普遍存在的。芳香族乙烯基聚合物的光电导是与这些基本过程密切相关的典型现象之一。由于芳香族侧基之间的相互作用很小，电子态的能带结构不合理，因此提出了这一载流子输运过程的跳跃模型。目前尚不清楚在分子水平上调节相邻两个芳香族基团之间电荷转移反应的因素。为了更深入地了解这一高效的电子转移反应，用皮秒和飞秒暂态吸收光谱和瞬时二向色性测量研究了聚N-乙烯基咔唑(PVCz)的光致电子转移动力学(电荷分离、电荷复合和空穴转移反应)以及溶剂对反应曲线的影响。在较极性的溶液中，电子转移动力学可以用咔唑(Cz)部分的阳离子状态沿着聚合物链中悬挂的Cz部分持续迁移的简单方案来描述。在飞秒-几皮秒的时间范围内的二向色性测量表明，阳离子在Cz单元上的离域对随后的空穴转移起着重要的作用。也就是说，离域导致有效离子间距离减小，从而降低初始对中的库仑吸引能，同时电子转移反应中重组能的降低也加速了空穴转移过程。

The transport of electrons initiated by photoexcitation is ubiquitous in nature as well as in artificial systems. Photoconductivity in aromatic vinyl polymers is one of the typical phenomena closely related to these fundamental processes. Since the band structures in the electronic states are not plausible because of rather small interaction among the pendant aromatic groups, hopping model has been proposed for this carrier transport processes. Still unclear are the factors regulating the charge shift reaction between two neighboring aromatic groups in a molecular level. To obtain deeper insights into this efficient electron transfer reaction, photoinduced electron transfer dynamics (charge separation, charge recombination and hole transfer reactions) in poly (N-vinylcarbazole) (PVCz) and solvent effects on the reaction profiles were studied by means of picosecond and femtosecond transient absorption spectroscopy and transient dichroism measurements.Electron transfer dynamics in PVCz in rather polar solutions was well described by the simple scheme that the cation state of carbazolyl (Cz+) moiety continuously migrates along pendant Cz moieties in the polymer chain with the charge recombination at the initial position of the charge separation. The dichroism measurement in femtosecond -a few picosecond time region revealed that the delocalization of the cationic state over Cz units takes an important role for the subsequent hole transfer. That is, the delocalization leads to the decrease in the effective inter-ionic distance to reduce the Coulombic attractive energy in the initial pair and also the decrease in the reorganization energy in the electron transfer reaction accelerates the hole transfer process.