Elementary excitations in electroluminescent one-dimensional conjugated polymers

最近在聚合物聚对苯乙炔（PPV）中发现的电致发光引起了人们对极化子（一维共轭聚合物中的一种非线性激发）的关注，极化子是通过电荷复合引起电致发光的电荷载流子的候选者。我们已经表明，ESR和ENDOR光谱是有用的观察共轭聚合物中的顺磁激发的微观形状。本计画的目的是对PPV及其衍生物在光照、掺杂等条件下产生的极化子进行ESR和ENDOR观测，并建立理论模型，对数据进行分析，得到极化子的形状以及聚合物的电子态。我们已经成功地确定了PPV中极化子的详细形状，并通过分析ENDOR和新获得的TRIPLE（电子-核-核三重共振）数据，由住友化学公司的T.Ohnishi博士提供。所获得的最大自旋密度位于亚乙烯基位点上的结果成功地解释了衍生物氰基PPV中ODESR线宽的降低，其中亚乙烯基位点的质子被氰基取代，由英国和美国的小组报道。除此之外，在Cavendish Laboratory的R.H.Friend教授提供的氰基取代PPV衍生物中，还成功地检测到了光生极化子的光诱导ESR（LESR）。目前正在对所观察到的LESR线形以及LESR强度的激发光谱进行分析，以研究分子结构对一维聚合物的极化子形状和电子态的影响。

Recent discovery of electroluminescence in a polymer, poly (phenylene vinylene) , PPV has brought much attention to polarons, a nonlinear excitation in one-dimensional conjugated polymers, as a candidate of charge carriers responsible for electroluminescence through charge recombination. We have shown that ESR and ENDOR spectroscopies are useful in observing the microscopic shapes of paramagnetic excitations in conjugated polymers. The purpose of the present project is to conduct ESR and ENDOR observations of polarons generated by light illumination, doping etc. in PPV and its derivatives and to develop a theoretical model to analyze the data to obtain the polaron shapes as well as the electronic states of polymers.In this year, we have been successful in determining the detailed shape of polarons in PPV and the magnitudes of Coulomb interactions affecting the shape by analyzing the ENDOR and newly obtained TRIPLE (electon-nuclear-nuclear triple resonance) data of trapped polarons in the dark state of the polymer, provided from Dr. T.Ohnishi of Sumitomo Chemical Co. The obtained results with the maximum spin densities reside on vinylene sites successfully explained the reduction of ODESR linewidth in a derivative, cyano-PPV where the protons of vinylene sites are substituted by cyano groups, reported by British and American groups. The results have been published in JPSJ.In addition to these, light-induced ESR (LESR) of photogenerated polarons has been successfully detected in cyano-substituted PPV derivatives provided from Prof. R.H.Friend of Cavendish Laboratory. The analysis of the observed LESR line shapes as well as the excitation spectra of LESR intensities are currently under progress to study the effect of molecular structures on the polaron shapes and the electronic states of one-dimensional polymers.