Aggregated states of luminescent conjugated polymers in solutions

In order to study the electronic properties of the interchain state in light-emitting polymers, we have performed spectroscopic experiments for 2,5-dioctyloxy PPV (DOO-PPV) in both good (chloroform) and poor (2-methyl-tetrahydrofuran) solvents. The concentration-dependent absorption, photoluminescence (PL) spectra and dynamics of time-resolved PL can be explained by the coexistence of an intrachain and one kind of aggregated states in poor solution. The estimated lifetime and transition moment of the aggregated state lead to significant quantum efficiency of PL which is about 0.75 times that of the intrachain state. The PL spectrum for the aggregated state resembles that of a thin film, implying that the emissive species in thin film is more likely to be an aggregated state.