Ultrafast Relaxation of the Poly(3-hexylthiophene) Emission Spectrum
Ultrafast Relaxation of the Poly(3-hexylthiophene) Emission Spectrum
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DOI：
10.1021/jp1119348
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发表时间：
2011-05-19
影响因子：
3.7
通讯作者：
Heeger, Alan J.
中科院分区：
文献类型：
--
作者：
Banerji, Natalie;Cowan, Sarah;Heeger, Alan J.
介绍了重要的共轭聚合物聚（3-己基噻吩）（P3HT）的飞秒分辨发射光谱演变。对P3HT固态薄膜和在氯苯溶液中的P3HT进行了详细的荧光上转换光谱分析。采用了两个激发波长和几个发射波长，覆盖了整个荧光光谱。这些数据由偏振敏感测量补充。我们的全局分析允许以200 Is的时间分辨率重建时间分辨发射光谱，因此可以全面表征原始聚合物中pi-pi*带间吸收后早期弛豫过程引起的光谱变化。吸收发生在溶液中孤立的聚合物链和薄膜的固态中（包括链间相互作用）。在这两种情况下，我们都发现了多余能量光激发后直接在能带上形成的电子和空穴离域的证据。随后是超快（类似于100fs）的初级光激发自定位和相对缓慢的激子形成（类似于1ps）。进一步的弛豫发生在几百飞秒到几十皮秒的时间常数范围内，这是由于激子跃迁到能量较低的位置以及聚合物主链的缓慢构象平面化。由于这种弛豫，可以观察到去极化、光谱红移和振动结构的重要变化。最后，在100- 200ps的时间尺度下，在溶液和薄膜中分别形成了松弛的链内和链间单线态激子。它们通过溶液中的系统间交叉和薄膜中的非辐射复合以类似500ps的时间常数衰减。我们的结果与我们从聚合物pcdbt的类似时间分辨荧光研究中得到的结论是一致的。化学。高分子学报，2010,32(1)：富勒烯共混物的超快电荷分离似乎发生在初级激发形成束缚激子之前。
The femtosecond-resolved evolution of the emission spectrum of the important conjugated polymer poly(3-hexylthiophene) (P3HT) is presented. Detailed fluorescence up-conversion spectroscopy was performed on P3HT solid-state films and on P3HT in chlorobenzene solution. Two excitation wavelengths and several emission wavelengths, covering the entire fluorescence spectrum, were used. The data were complemented by polarization-sensitive measurements. Our global analysis allowed a reconstruction of the time-resolved emission spectra with 200 Is temporal resolution, so that spectral changes due to the early relaxation processes following pi-pi* interband absorption in the pristine polymer could be comprehensively characterized. Absorption occurs in isolated polymer chains in solution and in the solid state (including interchain interactions) for the film. In both cases, we find evidence of delocalization of the electrons and holes formed in the energy bands directly after photoexcitation with excess energy. This is followed by ultrafast (similar to 100 fs) self-localization of the primary photoexcitation and by relatively slow exciton formation (similar to 1 ps). Further relaxation occurs with time constants ranging from hundreds of femtoseconds to tens of picoseconds, due to exciton hopping to sites with lower energy and to a slow conformational planarization of the polymer backbone. Depolarization, a spectral red shift, and important changes in the vibronic structure are observed as a consequence of this relaxation. Finally, relaxed intrachain and interchain singlet excitons are formed in solution and film, respectively, on a 100-200 ps time scale. They decay with a similar to 500 ps time constant, by intersystem crossing in solution and by nonradiative recombination in the film. Our results are consistent with and strongly support the conclusions we obtained from a similar time-resolved fluorescence study of the polymer PCDTBT (J. Am. Chem. Soc. 2010, 132, 17459): ultrafast charge separation in polymer:fullerene blends seems to occur before localization of the primary excitation to form a bound exciton.