RAMAN-SPECTRA AND GROUND-STATE OF THE NEW LOW BANDGAP POLYMER POLY(THIENOPYRAZINE)

Raman modes of the new processable polymer poly(2,3-alkyl-thieno[3,4-b ]-pyrazine) with a bandgap of about 0.9 eV were measured and calculate d. Raman spectroscopy revealed two strong lines at about 1520 cm(-1) a nd 1560 cm(-1) in the C=C stretching mode region. By changing the exci ting laser line these modes exhibit a dispersion of 16 and 25 cm(-1)/e V, respectively. Calculations on the ground state revealed that the qu inonoid structure is by about 13 kcal/mol per repeat unit more stable than the aromatic form. By using the scaled quantum mechanical oligome r force field method we calculated the Raman spectrum of the quinonoid form and identified the mode at 1520 cm(-1) as the inter-ring A(g) vi bration.