Ultrafast photoinduced charge generation in conjugated polymers

Transient excited-state absorption measurements in the spectral region spanning the infrared active vibrational active (IRAV) modes in prototypical luminescent polymers, poly(phenylene vinylene), PPV, and poly[2-methoxy-5-(2-ethyl-hexyloxy)-(phenylene vinylene)], MEH-PPV, reveal charge carrier generation within 100 fs after photoexcitation. The photocarrier quantum efficiency in MEH-PPV is phi(o) approximate to 0.1 in zero applied electric field. There is no correlation between the temporal behavior of the photoinduced IRAV signals and the exciton Lifetime. Thus, carriers are photoexcited directly and not generated via a secondary process from exciton annihilation. Our data indicate that the carrier recombination rate is sensitive to the strength of the inter-chain interaction. (C) 2000 Elsevier Science B.V. All rights reserved.