DYNAMICS OF SINGLET EXCITATIONS IN CONJUGATED POLYMERS - POLY(PHENYLENEVINYLENE) AND POLY(PHENYLPHENYLENEVINYLENE)

The decay of the photoluminescence of the conjugated polymers, poly(ph enylenevinylene), poly(phenylphenylenevinylene) (PPPV), and PPPV blend ed with polycarbonate is measured as a function of the position of the spectral detection window employing frequency-up-conversion and strea k-camera techniques. Upon probing at the high-energy side of the inhom ogeneously broadened S-1 <-- S-0 0-0 transition, an initial falloff ch aracterized by a (1/e) decay time of about 300 fs is observed. This de cay slows down by three orders of magnitude upon shifting the detectio n window towards lower energies. We present a quantitative analysis of these experimental data by performing simulations of dipole-dipole ex citation transfer on a random lattice chain with energetic site disord er. They give evidence for the notion that photon absorption generates neutral excitations undergoing a random walk among segments of the po lymer chain with different excitation energies.