A theoretical investigation of α,α′-dimethyl end-capped oligothiophenes: Structures, vibrational spectra and conjugational defects

Ab initio quantum-chemical methods are used in the study of the effect of ionization on the geometries and vibrational spectra of a series of α,α′-dimethyl end-capped oligothiophenes (from dimer to hexamer). For that purpose we determine the geometric structures, vibrational frequencies, and infrared and Raman intensities of neutral, radical cationic and dicationic oligomers. These theoretical data, when combined with the results of the experimental studies, provide a complete picture of the vibrational structure of the neutral state of doped oligomers.