Ultrafast energy transfer dynamics between block copolymer and /spl pi/-conjugated polymer

The quantum efficiency of the blended polymeric system consisting of poly[2-methoxy-5-(2-ethylhexyloxy)-l,4-phenylenevinylene] (MEH-PPV) and conjugated-nonconjugated multi-block copolymer (CNMBC), poly[l,3-propane-dioxy-1,4-phenylene-1,2-ethylene-(2,5-bis(trimethylsilyl)-1,4 -phenylene)-1,2-ethylene-1,4-phenylene] (DSiPV) is several times higher than that of the constituent polymers, which is explained in terms of the Forster energy transfer theory. But the ultrafast photoexcitation dynamics of MEH-PPV and of the blended polymer consisting of MEH-PPV and DSiPV using the time-resolved fluorescence and femtosecond transient absorption spectroscopic techniques suggests that other mechanisms should be involved. No apparent change in the absorption spectrum of the blended polymer (MEH-FPV:DSiPV=6:4 mass ratio) compared to those of MEH-PPV and DSiPV indicates that neither chemical nor conformational change has occurred upon mixing. Their time-integrated photoluminescence (PL) spectra show that upon blending, the emission from DSiPV disppears while that from MEH-PPV predominates with a slight red-shift of the emission maximum. The red-shifted PL spectrum and the disappearance of the stimulated emission (SE) in the transient absorption spectrum of the blended polymer clearly indicates that two different emissive states play roles in the relaxation process of the primary photoexcitations in MEH-PPV thin films.