TEMPERATURE EFFECTS ON RAMAN SPECTRA OF PEDOT AND MEH-PPV CONDUCTING POLYMERS

The present work shows the temperature dependence of the Raman spectra of two conjugated polymers: poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS). In situ resonance Raman spectra of PEDOT from 77 to 423 K at 633 nm and of MEH-PPV from 77 to 473 K at 785 nm suggest that, for both polymers, as the temperature increases there is a decrease in the chain conjugation length. Raman bands of PEDOT assigned to the νsim Cα-Cβ are the most sensitive to temperature while bands due to oxyethylene rings do not show significant shifts in this temperature range. Raman and FT-IR spectra of MEH-PPV recorded above the thermal decomposition temperature provide some insights about the thermal degradation.

本研究揭示了两种共轭聚合物（conjugated polymers）的拉曼光谱（Raman spectra）随温度的变化特征：聚[2-甲氧基-5-(2-乙基己氧基)-1,4-亚苯基亚乙烯基]（poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]，缩写MEH-PPV）与聚(3,4-乙撑二氧噻吩)-聚(苯乙烯磺酸盐)（poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)，缩写PEDOT:PSS）。通过633 nm激光激发、在77 K至423 K温度区间内采集的PEDOT原位共振拉曼光谱（in situ resonance Raman spectra），以及785 nm激光激发、77 K至473 K温度区间内采集的MEH-PPV原位共振拉曼光谱结果表明：两种聚合物的分子链共轭长度均随温度升高而缩短。PEDOT中归属为νsim Cα-Cβ的拉曼特征峰对温度变化最为敏感，而氧乙烯环对应的拉曼峰在该温度区间内未出现显著频移。在高于热分解温度的条件下测得的MEH-PPV拉曼光谱与傅里叶变换红外光谱（FT-IR spectra），为其热降解过程提供了若干关键见解。