FEMTOSECOND DYNAMICS OF EXCITONS IN PI-CONJUGATED OLIGOMERS - THE ROLE OF INTRACHAIN 2-EXCITON STATES IN THE FORMATION OF INTERCHAIN SPECIES

We report femtosecond transient absorption results for solutions and t hin films of a substituted oligomer of poly(para-phenylene vinylene) p erformed over wide spectral and pump-intensity ranges. Solutions and f ilms exhibit a photoinduced absorption (PA) band with dynamics matchin g those of the stimulated emission, demonstrating unambiguously that t hese features originate from intrachain singlet excitons. Thin films e xhibit an additional short-wavelength PA band with pump-independent dy namics, indicating the formation of non-emissive interchain excitons. Correlations in the dynamics of the two PA features, as well as the in tensity-dependence, provide strong evidence that the formation of inte rchain excitons is mediated by intrachain two-exciton states. (C) 1997 Elsevier Science B.V.