RESEARCH ON THE PRIMARY PROCESSES OF PHOTOCONDUCTION IN AROMATIC VINYL POLYMERS BY MEANS OF PICOSECOND AND FEMTOSECOND VISIBLE AND NEAR-IR LASER SPECTROSCOPY

由光激发引发的电子输运在自然界和人工系统中普遍存在。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。由于电子态的能带结构是不合理的，因为相当小的相互作用的侧芳基，跳跃模型已被提出的载流子输运过程。在分子水平上调控两个相邻芳香基团之间电荷转移反应的因素还不清楚。为了更深入地了解这种有效的电子转移反应，（电荷分离，电荷复合和空穴转移反应（N-乙烯基咔唑）（PVCz）利用皮秒和飞秒瞬态吸收光谱和瞬态二向色性测量研究了PVCz和溶剂效应对反应曲线的影响，并利用瞬态二向色性测量很好地描述了PVCz在较强极性溶液中的电子转移动力学。简单的方案，咔唑基（Cz^+）部分的阳离子状态连续迁移沿着侧链Cz部分在聚合物链中的电荷复合在电荷分离的初始位置。在吡啶溶液中，空穴从Cz^+向相邻的Cz^+转移的速率常数为（230 ps）^<-1>。随着溶剂极性的降低，HT速率常数急剧降低，其为[小于或等于]约。氯仿<-1>溶液中10^7s^。这种溶剂极性的影响不仅占在有吸引力的库仑相互作用与溶剂极性的降低，但也通过离域的阳离子状态超过Cz单元的增加。将所得结果与其它芳香族乙烯基聚合物的结果相结合，讨论了芳香族乙烯基聚合物中空穴转移过程的影响因素。

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. Rate constant of the hole transfer (HT) from the Cz^+ to neighboring ones was (230 ps)^<-1> in pyridine. With a decrease in the solvent polarity, the HT rate constants drastically decreased and it was 【less than or equal】 ca. 10^7s^<-1> in chloroform solution. This solvent polarity effect was accounted for not only by the increase in the attractive Coulombic interaction with decreasing solvent polarity but also by the delocalization of the cationic state over Cz units. By integrating the present results with those in other aromatic vinyl polymers, the factors regulating the hole transfer process in aromatic vinyl polymers were discussed.