Two-dimensional Raman spectroscopic study on the structural changes of a poly(3-chlorothiophene) film during the heating process

Two-dimensional Raman spectroscopy has been applied to provide the information on charge carriers and thermal stability of a doped poly(3-chlorothiophene) (PCTh) film. The strong spectral intensity at 1420 cm⁻¹ shows that positive polarons are the major charge carriers in doped PCTh. On the other hand, peaks in the 2D contour maps separate the overlapped bands around 1386 cm⁻¹, confirming the existence of positive bipolarons in PCTh. The positive asynchronous cross peak located at 1420/1386 cm⁻¹ further indicates that bipolarons have a higher thermal stability compared with polarons in the doped PCTh. The increase of the spectral intensity at 1454 cm⁻¹ and the decrease of the spectral intensity at 1420 cm⁻¹ indicate that during the heating process, a structural change occurs in the PCTh film.