Random growth statistics of long-chain single molecule poly-(p-phenylene vinylene)

Structures of poly-(p-phenylene vinylene) (PPV) were generated using a random growth algorithm. The algorithm assumes that the configuration of a part of the polymer (a few monomers length) can be sampled from the configuration of a PPV trimer. The probabilities of the configurations of the trimer are taken as the Boltzmann weight of the energies. We constructed several types of polymers with different numbers of cis-defects which were added to the polymer either uniformly or randomly distributed within the entire polymer. Polymer characteristics, such as conjugation length, end-to-end distance, and radius of gyration, were also calculated. The trends of these characteristics were found to be inversely proportional with the number of cis-defects in the polymer. Although average conjugation lengths are generally independent of the distribution of cis-defects, the morphology of the polymer is dependent on cis-defect distribution. This suggests that conformational disorder rather than cis-defect density is the determining factor in exciton localization and diffusion in these systems. Finally, we derive a simple model similar to the Ising model that relates the energy needed to break conjugation to the average conjugation length. (C) 2001 American Institute of Physics.