Temperature effects on quasi-isolated conjugated polymers as revealed by temperature-dependent optical spectra of 16-mer oligothiophene diluted in a sold matrix.
Temperature effects on quasi-isolated conjugated polymers as revealed by temperature-dependent optical spectra of 16-mer oligothiophene diluted in a sold matrix.
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DOI：
10.1063/1.3152447
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发表时间：
2009-06
期刊：
影响因子：
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通讯作者：
K. Kanemoto;I. Akai;M. Sugisaki;H. Hashimoto;T. Karasawa;N. Negishi;Y. Aso
中科院分区：
文献类型：
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作者：
K. Kanemoto;I. Akai;M. Sugisaki;H. Hashimoto;T. Karasawa;N. Negishi;Y. Aso
为了阐明温度对准分离共轭聚合物的影响，研究了在聚丙烯（PP）中极稀释的16聚寡硫吩（16 T）的光致发光（PL）和吸收光谱的温度依赖性（4-300 K）。发光光谱和吸收光谱随温度的升高而发生蓝移。通过比较溶剂（PP）折射率模型和16 t热构象变化模型，讨论了蓝移产生的原因，得出蓝移是热构象变化的结果。时间分辨PL光谱显示出光激发后PL波段的红移（光谱迁移）。迁移量随着温度的升高而增加。运移增加的原因是热构象的变化。计算了16 T的有效共轭长度（ECL）对吸收和PL跃迁的温度依赖性。计算表明，ECL在室温下减少到本征链长的三分之二。根据ECL的温度依赖性，估计构象变化的活化能为22.4 meV。我们证明了在很宽的温度范围内，使用单一的Huang-Ryes因子，通过简单的frank - condon分析可以很好地再现稳态PL光谱。分析揭示了Stokes位移、线宽和Huang-Ryes因子等重要光谱参数的温度依赖特征。
Temperature dependences (4-300 K) of photoluminescence (PL) and absorption spectra of 16-mer oligothiophene (16 T) extremely diluted in polypropylene (PP) have been investigated in order to clarify temperature effects on quasi-isolated conjugated polymers. The PL and absorption spectra are found to blueshift with increasing temperature. The reason for the blueshift is discussed by comparing models based on the refractive index of the solvent (PP) and on the thermal conformational change of 16 T. The blueshift is concluded to result from the thermal conformational change. Time-resolved PL spectra show a redshift of PL band following photoexcitation (spectral migration). The amount of the migration is shown to increase with increasing temperature. The increased migration is concluded to be due to the thermal conformational change. The temperature dependence of the effective conjugation length (ECL) of 16 T is calculated for the absorption and PL transitions. The calculation suggests that ECL is reduced at room temperature to two-thirds of the intrinsic chain length. The activation energy of the conformational change is estimated to be 22.4 meV from the temperature dependence of ECL. We demonstrate that the steady-state PL spectra are well reproduced by simple Franck-Condon analyses using a single Huang-Ryes factor over a wide temperature range. The analyses reveal features of temperature dependence in important spectral parameters such as the Stokes shift, linewidth, and Huang-Ryes factor.