Two-photon ultrafast spectroscopy of DOO-PPV thin films

We measured the ultrafast dynamics of photoexcitations in thin films of poly(2,5 dioctyloxy p-phenylene vinylene)-[DOO-PPV] by applying the femtosecond transient two-photon pump and probe photoinduced absorption technique. We found that the excited even parity state, namely the mA g state decays into the lowest lying odd parity exciton state (1B u ) within 200fs (the resolution of our pump-probe setup). The long-lived photoinduced absorption (PA) component that follows the ultrafast internal conversion process has the same time constant as the excitonic PA in one-photon excitation at moderately high intensities; we therefore identify this PA component as decay of photogenerated excitons.