In the framework of quantum field theory and the dipole approximation, a self-consistent quantum molecular dynamics method is used to investigate the effect of chain length on the probability of formation or decay of both singlet and triplet excitons due to photon absorption or emission in isolated poly(p-phenylene vinylene) (PPV) chains. We found that the probability of the photoinduced intra-molecular singlet exciton formation and decay increases linearly with chain length and the probability for triplet exciton formation and decay does not depend on the chain length. Polymers with long chains have thus an advantage over small molecules in solar cell and light-emitting diode (LED) applications because their efficiency depends on the number of intramolecular singlet excitons formed or emitted in the device, which is expected to increase with the conjugation length. (c) 2005 Elsevier B.V. All rights reserved.