RESEARCH ON THE PRIMARY PROCESSES OF PHOTOCONDUCTION IN AROMATIC VINYL POLYMERS BY MEANS OF PICOSECOND AND FEMTOSECOND VISIBLE AND NEAR-IR 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。芳香乙烯基聚合物中的光电导率是与这些基本过程密切相关的典型现象之一。由于悬垂芳基之间的相互作用很小，导致电子态的能带结构不合理，因此提出了跳变模型来描述这种载流子输运过程。在分子水平上调控两个相邻芳香族间电荷移位反应的因素尚不清楚。为了更深入地了解这种高效的电子转移反应，利用皮秒和飞秒瞬态吸收光谱和瞬态二色性测量，研究了聚n -乙烯基咔唑（PVCz）中光诱导电子转移动力学（电荷分离、电荷复合和空穴转移反应）和溶剂对反应谱的影响。用咔唑基（Cz^+）阳离子态沿聚合物链上挂起的Cz基团连续迁移并在电荷分离的初始位置发生电荷重组的简单方案很好地描述了偏极性溶液中PVCz的电子转移动力学。在吡啶中，从Cz^+到邻近的空穴转移（HT）的速率常数为（230 ps）^<-1>。随着溶剂极性的降低，高温反应速率常数急剧降低，在氯仿溶液中，高温反应速率常数<小于等于10^7s^<-1>。这种溶剂极性效应不仅是由于吸引库伦相互作用随着溶剂极性的降低而增加，而且是由于阳离子态在Cz单元上的离域。结合其他芳香族乙烯基聚合物的研究结果，讨论了影响芳香族乙烯基聚合物空穴转移过程的因素。

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.