In this paper, we report a simple procedure to decouple effects from temperature and volume on the emission properties of thin films of poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV). This procedure consists of applying a positive pressure close to the β-relaxation temperature, T_β (∼220 K), of MEH-PPV, which controls the molecular movement to retain a disordered state for the polymer chains even after the sample is cooled from room temperature. Such decoupling could be confirmed by calculating the photoluminescence (PL) spectra line shape using a semi-empirical model based on molecular exciton and Franck–Condon transitions, and with electron–vibrational modes coupling being parameterized with the Huang–Rhys factor. We also show that the decoupling between temperature and volume effects does not occur if the molecular movement is restricted either by thermal annealing or by depositing the MEH-PPV film on a rigid substrate. This latter finding may be exploited in designing thermally stable devices.

中文翻译：

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在β-松弛温度下对聚[2-甲氧基-5-（2'-乙基己氧基）-1,4-亚苯基-亚乙烯基]薄膜的去耦温度-体积效应。

在本文中，我们报告了一种简单的程序，可将温度和体积对聚[2-甲氧基-5-（2'-乙基己基氧基）-1,4-亚苯基-亚乙烯基]（MEH- PPV）。此过程包括施加正压力接近β-松弛温度的，Ť _β（〜220 K），MEH-PPV，即使样品从室温冷却后也能控制分子运动以保持聚合物链的无序状态。通过使用基于分子激子和Franck-Condon跃迁的半经验模型计算光致发光（PL）光谱线形，并使用Huang-Rhys因子对电子-振动模式耦合进行参数化，可以确认这种解耦。我们还表明，如果分子运动受热退火或通过在刚性基板上沉积MEH-PPV膜限制，则不会发生温度与体积效应之间的解耦。后一发现可用于设计热稳定装置。