Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588, Japan.
Department of Advanced Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan.
Molecules. 2019 Jan 25;24(3):431. doi: 10.3390/molecules24030431.
The initial charge separation process of conjugated polymers is one of the key factors for understanding their conductivity. The structure of photogenerated transients in conjugated polymers can be observed by resonance Raman spectroscopy in the near-IR region because they exhibit characteristic low-energy transitions. Here, we investigate the structure and dynamics of photogenerated transients in a regioregular poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C-butyric acid methyl ester (PCBM) blend film, as well as in a pristine P3HT film, using femtosecond time-resolved resonance inverse Raman spectroscopy in the near-IR region. The transient inverse Raman spectrum of the pristine P3HT film at 50 ps suggests coexistence of neutral and charged excitations, whereas that of the P3HT:PCBM blend film at 50 ps suggests formation of positive polarons with a different structure from those in an FeCl₃-doped P3HT film. Time-resolved near-IR inverse Raman spectra of the blend film clearly show the absence of charge separation between P3HT and PCBM within the instrument response time of our spectrometer, while they indicate two independent pathways of the polaron formation with time constants of 0.3 and 10 ps.
共轭聚合物的初始电荷分离过程是理解其导电性的关键因素之一。通过共振拉曼光谱在近红外区域可以观察到共轭聚合物中光生瞬态的结构，因为它们表现出特征的低能量跃迁。在这里，我们使用飞秒时间分辨近红外区域的共振反拉曼光谱研究了在一个区域规整的聚（3-己基噻吩）（P3HT）：[6,6]-苯基-C-丁酸甲酯（PCBM）共混膜以及在纯 P3HT 膜中的光生瞬态的结构和动力学。在 50 ps 时，纯 P3HT 膜的瞬态反拉曼光谱表明中性和带电激发态共存，而在 50 ps 时，P3HT：PCBM 共混膜的瞬态反拉曼光谱表明形成了与 FeCl₃掺杂的 P3HT 膜中不同结构的正极化子。共混膜的时间分辨近红外反拉曼光谱清楚地表明，在我们光谱仪的仪器响应时间内，P3HT 和 PCBM 之间不存在电荷分离，而它们随着时间的推移表明了极化子形成的两条独立途径，其时间常数分别为 0.3 和 10 ps。
