Relaxation of excitons and charge carriers in polymers

In this paper various aspects of relaxation of optically generated excitations in random organic solids are discussed. Examples are spectral diffusion of excitons in organic glasses, or conjugated polymers, involving energy transfer within an inhomogeneously broadened dense manifold of chromophores, and charge carrier transport in random photoconductors. After an outline of the concept of time dependent random walks within an energetically and spatially disordered array of hopping sites, recent results on charge and exciton transport in π-conjugated systems such as conjugated polymers will be presented. The main emphasis will be on site-selective methods. Site selectivity, achieved by means of a spectrally tunable excitation source, is an unique opportunity to identify a subensemble of excitations which will be able to undergo subsequent relaxation probed by time-dependent spectroscopy