Evidence of polarized charge-transfer transitions by probing the weak dielectric tensor components of oligothiophene crystals

The absorption spectra of different oligothiophene single crystals without saturation effects in a wide spectral range are reported and compared. The origin of the main ac polarized broad band is discussed in terms of Frenkel excitons. Exploiting experimental configurations which correspond to the excitation of the weak dielectric tensor components, bands of different nature are also detected at different positions for orthogonal polarizations and attributed to transitions of charge-transfer character.