Resonance Raman and ultraviolet to infrared absorption studies of positive polarons and bipolarons in sulfuric-acid-treated poly(p-phenylenevinylene)

The resonance Raman and infrared spectra of sulfuric-acid-treated poly(p-phenylenevinylene) (PPV) have been observed and analyzed on the basis of the resonance Raman spectra of the radical-cation and dication species of the model compounds CH₃(C₆H₄CH=CH)_nC₆H ₄CH₃ (PVn, n = 1-3), which correspond, respectively, to positive polarons and bipolarons in PPV. Sulfuric-acid-treated PPV is considered to contain a considerable amount of positive polarons having a more or less uniform length and a relatively small amount of positive bipolarons. Of the two electronic absorption bands at 2.25 and 1.00 eV of sulfuric-acid-treated PPV, the former absorption band is due to the positive polarons, whereas the latter has overlapping components arising from the positive polarons and bipolarons. It is suggested that the high electrical conductivity of sulfuric-acid-treated PPV may be due to formation of a polaron lattice, a regular array of polarons.