Multiple pulse transient spectroscopy in luminescent pi-conjugated polymers

We closely examined relaxation processes between even and odd parity excitons in poly(p-phenylene vinylene) derivative polymers using a multiple femtosecond pulse transient spectroscopy. By tuning the energy of re-excitation and probe pulses across a wide spectral range, we were able to measure a complete spectrum of the 1B(u) exciton and also probe its counterparts: higher lying mA(g) and kA(g) excitons. Dramatically different relaxation paths were found for two later states: whereas the majority of mA(g) excitons experience an ultrafast internal conversion back to their 1B(u) state, most of kA(g) excitons transform into a non-emissive state, which we attribute to weakly bound polaron pairs. (C) 2001 Published by Elsevier Science B.V.