Optical properties of electropolymerized polyparaphenylene

Abstract We present an optical study of polyparaphenylene samples polymerized by electoreduction of 4-4′ dibromo-biphenyl. By elemental analysis, a smaller amount of remaining bromine atoms is found with respect to PPP samples synthesized by the “Yamamoto” procedure. The optical absorption spectrum of these films (or pressed pellets) is composed of a main peak at ≅ 380–390 nm with a shoulder at ≅ 410–420 nm. By comparison with the absorption bands observed for PPP “Kovacic” or PPP “Yamamoto”, these results seem to indicate a dispersion in the chain length of the polymer. In particular, a contribution of longer chain than in PPP “Kovacic” can be estimated. Also, fluorescence spectra show a different behavior. The infrared spectra of these electropolymerized films have been analyzed. A comparison between the ν 1 (800 cm −1 ), {ν 2 (760 cm −1 ) and ν 3 (690 cm −1 )} infrared modes has been made and the results are indicative of an average value of ≅ 14 for the number of phenyl rings in the polymer chain. Raman experiments have been performed with different excitation wavelengths. No frequency dispersion for the 1600 cm −1 Ag Raman mode is observed but, as already reported, different relative intensities for the 1220 cm −1 and 1280 cm −1 modes are detected as a function of λ L . These experimental data agree well with the hypothesis of a dispersion in the chain length of these electropolymerized PPP samples (specially derived from an u.v. excitation wavelength), and particularly of a contribution of rather long chains.