Spectroscopic studies on ultrathin poly(p-phenylenevinylene) film deposited by self-assembly and spin-coating methods

We report changes in the bandgap of poly(p-phenylenevinylene) (PPV) achieved by physical means. We describe the use of the variant of the self-assembly (SA) technique based on electrostatic attraction between opposite charges [1] to fabricate microstractured thin films of PPV on the solid substrate. The photoluminescence from these films is compared to that from unstructured thin films produced by spincoating and solution-casting. The fluorescence of self-assembled films is blue-shifted with respect to the spin-coated and solution-cast films (maximum photoluminescence at 494 nm, 515 nm and 545 nm, respectively), indicating that the average conjugated unit is shorter. We also investigate systematically the effect of added salt on the effective conjugation lengths of PPV prepared by heat-treatment from precursor polymer adsorbed on the oppositelycharged surface. We find that high ionic concentrations lead to a blue shift of the fluorescence (476 nm cf 551 nm for bulk material).