Optical excitations in poly(2,5-thienylene vinylene)

We present the results of spectroscopic studies of the electronic structure of the conjugated polymer poly(2,5-thienylene vinylene). Photoexcitation above the band gap at 1.8 eV gives rise to two transient absorption peaks at 0.44 and 1.0 eV that are associated with bipolarons that live for times of order a few milliseconds at 80 K. Photoluminescence, comparable in intensity to the Raman scattering, is found at energies above the band edge, and we assign this to a hot recombination process. We also report the Raman spectrum, and make a preliminary assignment of the main vibrational modes. Three of the four main peaks disperse as the excitation wavelength is varied. We discuss these results and compare them with those previously reported for a related polymer, poly-(p-phenylene vinylene).