Excitonic nonlinearity of regioregular π-conjugated polymer

我们研究了聚噻吩衍生物聚(3-[2-（(S)-2-甲基丁氧基）乙基]噻吩的激子非线性，它具有良好的结构规整性。我们的研究集中在两点上；1)激子非线性对有效共轭长度的依赖；2)激子的弛豫机制。我们的研究结果如下：1)用简并四波混频法测量了聚噻吩衍生物聚（3-[2-(S)-2-甲基丁氧基）乙基]噻吩的自旋涂层薄膜和Langmuir-Blodgett （LB）薄膜中激子共振周围的三阶光学非线性。得到了共轭聚合物中最大的χ^<(3)>值（~ 10^<-7 >esu）。通过对吸收光谱和χ^<(3)>光谱的拟合，估计自旋涂膜和LB膜的平均有效共轭长度分别约为20和36个噻吩环。2)从振动结构和动力学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（PL）来自于由奇宇称1Bu组分和偶宇称2Ag组分组成的两种混合态。由于两种状态的荧光具有不同的时间常数和不同的振动结构，因此PL表现出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PL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.