Ultrafast photoinduced charge generation in conjugated polymers

Transient excited-state absorption measurements in the spectral region span ning the infrared active vibrational active (IRAV) modes in prototypical lu minescent polymers, poly(phenylene vinylene), PPV, and poly[2-methoxy-5-(2- ethyl-hexyloxy)-(phenylene vinylene)], MEH-PPV, reveal charge carrier gener ation within 100 fs after photoexcitation. The photocarrier quantum efficie ncy 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 dire ctly and not generated via a secondary process from exciton annihilation. O ur data indicate that the carrier recombination rate is sensitive to the st rength of the inter-chain interaction. (C) 2000 Elsevier Science B.V. All r ights reserved.