Dichroism in photoinduced infrared spectra of polyalkylthiophenes

The photoinduced infrared spectra of stretch‐oriented polyhexylthiophene and polyoctylthiophene are reported as a function of the polarization both of the pump light and of the probe IR beam. There is no change in the intensity of photoinduced IR absorption due to the polarization of the pump; however, the spectra show parallel dichroism when the probe is polarized. The experimental results are analyzed on the basis of the “effective conjugation coordinate” theory (ECC).