Picosecond hopping relaxation in conjugated polymers

The energy relaxation of optical excitations in poly(p-phenyl-phenylenevinylene) (PPPV) and PPPV blended in polycarbonate (PC) is investigated by means of picosecond time-resolved luminescence spectroscopy. In PPPV a pronounced dependence on the photon energy of the excitation laser is found. For excitation into the tail states of the inhomogeneously broadened density of states distribution, the spectral shape of the luminescence remains almost constant with time. However, a transient red-shift is observed for excitation at higher energies. Experiments on the diluted system PPPV / PC allow us to distinguish between intra-and inter-chain processes. The experimental results can be explained with a hopping model.