Dynamics of singlet excitations in conjugated polymers: Poly(phenylenevinylene) and poly(phenylphenylenevinylene)

The decay of the photoluminescence of the conjugated polymers, poly(phenylenevinylene), poly(phenylphenylenevinylene) (PPV), and PPPV blended with polycarbonate is measured as a function of the position of the spectral detection window employing frequency-up-conversion and streak-camera techniques. Upon probing at the high-energy side of the inhomogeneously broadened S₁{←}S₀ 0-0 transition, an initial falloff characterized by a (1/e) decay time of about 300 fs is observed. This decay slows down by three orders of magnitude upon shifting the detection window towards lower energies. We present a quantitative analysis of these experimental data by performing simulations of dipole-dipole excitation transfer on a random lattice chain with energetic site disorder. They give evidence for the notion that photon absorption generates neutral excitation undergoing a random walk among segments of the polymer chain with different excitation energies.