Aggregation effects on the structure and optical properties of a model PPV oligomer

We report the effects of solvent-induced aggregation on photoluminescence spectra, decay dynamics and quantum yield in trimers of MEH-PPV and compare these to analogous experiments on the high molecular weight polymer. Nuclear magnetic resonance spectra imply that torsional motion is quenched by aggregation leading to a conjugation length increase that explains red shifts in the photoluminescence. We ascribe reduction of fluorescence quantum yield to interchain effects and observe anomalously long-lived luminescence ascribed to geminate recombination of polaron pairs. The decay dynamics suggest that, unlike the polymer case, we are able to time resolve the formation of polaron pairs in the aggregated trimer.