Photoelectronic characteristics of poly(p-phenylene vinylene) in self-assembled multilayer films

Self-assembly(SA) technique based on the electrostatic interactions between cationic and anionic polyelectrolytes provided a viable means to fabricate polymers into multilayer thin films. The self-assembled films made from poly(p-phenylene vinylene) (PPV) precursor and poly(sodium 4-styrenesulfonate) (PSS) were prepared, and their layer-by-layer growth and the changes of the conjugation lengths and the photoluminescence (PL) spectra after annealing were compared with those of spin-coated bulk PPV films. PPV precursor/PSS multilayer thin films showed stable growth behavior proportional to the number of deposition. The observed thermal conversion behavior toward the conjugated structure in the self-assembled films which was quite different from that of spin-coated films suggests that the conformational constraint on PPV precursor chains imposed by self-assembling process imparts limitation of conjugation length and its distribution. The self-assembled films with different conjugation lengths were also found to demonstrate almost the same PL spectra, whose emission wavelength and shape were quite different from those of the spin-coated PPV films. It is believed that such PL spectral characteristics of the self-assembled films are due to the hindrance on exciton migrations between PPV chains (or layers) which is caused by PSS chains (or layers).