A THEORETICAL INVESTIGATION OF ALPHA,ALPHA'-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 o f alpha,alpha'-dimethyl end-capped oligothiophenes (from dimer to hexa mer). For that purpose we determine the geometric structures, vibratio nal frequencies, and infrared and Raman intensities of neutral, radica l cationic and dicationic oligomers. These theoretical data, when comb ined with the results of the experimental studies, provide a complete picture of the vibrational structure of the neutral state of doped oli gomers.