ANION AND CATION ABSORPTION-SPECTRA OF CONJUGATED OLIGOMERS AND POLYMERS

The absorption spectra of chemically oxidized and reduced oligo(phenylenevinylene)s, 2,5-distyryl-thiophene, and poly(phenylphenylenevinylene) are reported. The essential conclusions are: (i) In all cases it is the radical ion that is the energetically favored species. (ii) OPV forms divalent anions in the course of a second reduction step while PPPV forms divalent anions and cations in the presence of an excess of reductant or oxidant. (iii) Oxidation/reduction of the polymer is a consecutive process starting with those chain segments having the longest effective conjugation lengths. (iv) The polaron concept is found inappropriate for spectral analysis. Instead, it is proposed that the spectra have to be assigned to transitions among molecular orbitals of the oligomers and polymer chain segments, respectively.