Layer-by-layer (LBL) thin films of a poly(p-phenylenevinylene) (PPV) precursor have been
processed using the long chain dodecylbenzenesulfonate anion (DBS). We adopted the alternative approach
with controlled substitution of the chloride counterion of the water-soluble PPV precursor by DBS. The
internal layer structure of these films is likely to be different from conventional LBL films, since DBS is
incorporated into the PPV precursor chain. In addition to the fast adsorption of the sulfonic salt,
introducing DBS allows the films to be converted at 110 °C within 12 min with a high conjugation length.
By varying the amount of DBS in the solution, the conjugation length of the PPV segments can be
controlled. The luminescence and absorption spectra show intense vibronic structures that are better
resolved than for cast and Langmuir−Blodgett films of PPV. LBL films converted at lower temperatures
display higher quantum efficiency, owing to the absence of carbonyl groups arising from high-temperature
conversion procedures.
Site-selective luminescence spectroscopy (SSL) was employed to resolve the vibracional modes in selfassembled poly(p-phenylene vinylene), PPV. Using Franck-Condon analysis, the PPV spectra can be well described by three effective vibrational modes at 330, 1160 and 1550 cm −1 . As the temperature increases from 4 to 180 K the electron-phonon coupling (S factor) remains constant for the 1550 cm −1 mode while for other lower energy modes the coupling increases monotonically. This trend is consistent with the decrease of the conjugation length due to the increase of thermal disorder. We find that the temperature dependence of vibrational progression in PPV films is determined mainly by low frequency torsional modes.
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