The difference of Raman spectra between lightly and heavily Na-doped trans-polyacetylene (trans-PA) was observed with the 1320 nm laser line, and these were discussed on the basis of the Raman spectra of the negatively charged anions Ph(CH)nPh- [DPn-, n = 3, 5, 7, 9, and 13] and the radical-anion species Ph(CH)nPh.- [DPn.-, n = 4, 6, 8, and 10] and 19,19′,20,20′-tetranor-β,β′-carotene [TNBC.-, n = 22] of the model compounds, which correspond respectively to negatively charged soliton and negative polarons in trans-PA. The observed wavenumbers of the v1 and v4 bands (C=C and C-C stretches) of lightly doped trans-PA are lower than those of the corresponding bands of pristine trans-PA, whereas the contrary is the case for heavily doped trans-PA. Raman spectra of the negatively charged soliton models (DPn-) and the negative polaron models (DPn.- and TNBC.-) were very similar to their spectrum patterns as a whole, but their wavenumbers and relative intensifies are mutually different to some extent. In particular, the Raman wavenumbers of heavily doped trans-PA are very similar with those of the polaron models. The dispersion of the C=C stretching band (ν1) in doped PA with the various wavelengths of excitation laser line were explained as the presence of charged domains having various lengths of electron localization.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry