Studies of Raman scattering in novel disubstituted acetylene polymers

We have studied resonant and non-resonant Raman scattering spectra in thin films of novel disubstituted acetylene polymers such as poly(l-ethyl-2-phenylacetylene) (PEtPA), poly(l-n-hexyl-2-phenylacetylene) (PHxPA) and poly(l-phenyl-2-/wibutylphenylacetylene) (PDPA-nBu), which possess high photoluminescence (PL) quantum efficiency. We found that the Raman scattering frequency dispersion is smaller in disubstituted acetylene polymers than in other acetylene polymers, in agreement with many other strongly luminescent polymers. Assuming the model of short polyene conjugation length in these acetylene polymers, we can obtain the conjugation length (N) for each polymer from the respective phonon frequency of the carbon-carbon double bond; we obtained N=7 for PDPA-nBu, and N=5 or 6 for PHxPA and PEtPA. The related energies of llBu and 2!Ag can be estimated from these N and are in good agreement with the respective absorption and PL spectra of the various disubstituted polymers.