Optical studies of electronic states and coupled vibrations in substituted polyacetylene

The electronic states and coupled vibrations in films of substituted polyacetylene (poly(o-trimethylsilylphenylacetylene); PTMSiPA) have been studied using the techniques of resonant Raman scattering (RRS) and electroabsorption (EA) spectroscopies. Strong RRS frequency dispersion has been observed for the C-C and C=C stretching vibrations with excitation photon energy from 1.55 to 3.42 eV, which is similar to that of other nonluminescent conducting polymers such as trans-polyacetylene, polydiacetylene and polydiethynylsilane. The RRS dispersion has been analyzed by means of the amplitude mode formalism placing the energy of the first allowed odd-parity exciton E(1Bu) of the longest chains at 1.85 eV. The rather weak EA spectrum is mainly composed of Stark shift of an energy distribution of 1Bu exciton and a positive contribution centered at 2.6 eV due to an even-parity exciton (mAg).