Excitonic nonlinearity of regioregular π-conjugated polymer

研究了结构规整性较好的聚噻吩衍生物poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene)，的激子非线性。我们的研究集中在两个方面：1)激子非线性对有效共轭长度的依赖关系，2)激子的驰豫机制。研究结果如下：1)用简并四波混频的方法测量了旋涂膜和聚噻吩衍生物的朗缪尔-布洛杰特(LB膜)膜中激子共振附近的三阶光学非线性，得到了poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene)，。得到了共轭聚合物中最大的χ^&lt；(3)&gt；值(~10^&lt；-7&gt；esu)。通过对吸收光谱和χ^-lt；(3)&gt；谱的拟合，估算出旋涂膜和LB膜的平均有效共轭长度分别约为20个和36个噻吩环。2)从振动结构和动力学的角度分析了聚噻吩衍生物的时间分辨光致发光光谱。我们发现，光致发光是由奇宇称1BU分量和偶宇称2Ag分量组成的两个混合态。由于这两个态的荧光具有不同的时间常数和不同的振动结构，发光呈现双指数衰减和光谱变化。该模型也很好地解释了许多其他π共轭聚合物的光致发光光谱及其动力学。

We investigated excitonic nonlinearity of polythiophene derivative poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene), which has good regularity in structure. Our study focused two points ; 1) the dependence of excitonic nonlinearity on the effective conjugation length, 2) the relaxation mechnism of exciton. Our research results are following ;1) Third-order optical nonlinearity around excitonic resonance in spincoated films and Langmuir-Blodgett (LB) films of polythiophene derivative, poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene), is measured using degenerate four wave mixing method. The largest χ^<(3)> value (〜10^<-7> esu) in conjugated polymers is obtained. By a fitting procedure on absorption spectrum and χ^<(3)> spectrum, the average effective conjugation lengths of the spincoated film and the LB film are estimated to be approximately 20 and 36 thiophene rings, respectively.2) The time-resolved photoluminescence spectrum of a polythiophene derivative has been analyzed from the viewpoint of the vibronic structure and its dynamics. We found that the photoluminescence (PL) originates from two mixed states that consist of the odd-parity 1Bu component and the even-parity 2Ag component. Since the fluorescence from the two states have different time constants and different vibronic structure, the PL shows a biexponential decay and a spectral change. This model also explains the PL spectrum and its dynamics of many other π conjugated polymers quite well.