Effects of aggregation on the excitation transfer in perylene-end-capped polyindenofluorene studied by time-resolved photoluminescence spectroscopy -art. no. 195203

We have investigated the excitation transfer in a system comprising poly(6, 6',12,12'-tetra-2- ethylhexyl-2,8-indenofluorene) (PIFTEH) chains end-cappe d with perylene dye molecules, using femtosecond time-resolved photolumines cence (PL) spectroscopy as well as polarized photoluminescence measurements . The transfer of excitons from isolated PIFTEH chains to perylene molecule s is completed within the first 30-40 ps after excitation, and we extract a Forster radius R-0=(1.8+/-0.3) nm from the time-resolved PL transients. We have modelled the polarization anisotropy for a guest-host system subject to Forster interactions via a Monte Carlo simulation and find that the emis sion from acceptors becomes unpolarized at sufficiently large acceptor conc entrations, permitting an accurate determination of the Forster radius from time-integrated photoluminescence anisotropy measurements. While spectral overlap calculations predict a large efficiency for the transfer of excitat ions to the perylene molecules from sites where the PIFTEH chains aggregate , no transfer is observed experimentally, which we attribute to chain packi ng effects within the sample prohibiting sufficiently close contact between PIFTEH aggregates and perylene molecules.