Multilayered Structures and Low Temperature Conversion Process of Poly( P -Phenylene Vinylene) Thin Films
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Multilayered Structures and Low Temperature Conversion Process of Poly(P-Phenylene Vinylene) Thin Films A. Marletta1, F. A. Castro, O. N. Oliveira Jr., R. M. Faria and F. E. G. Guimarães 1 Instituto de Física de São Carlos, Universidade de São Paulo, C.P. 369, 13560-970, São CarlosSP, Brazil.
ABSTRACT We have used a long chain dodecylbenzenesulfonate ion (DBS) to produce self-assembled multilayer structures of poly(p-phenylene vinylene) (PPV) with special features. Rather than alternating layers provided of a PPV-precursor (the poly(xylylidene tetrahydrothiophenium chloride or PTHT) and a polyanion, the alternated adsorption process was carried out with the PPV-precursor and the DBS ions in aqueous solution. The internal layer structure of these PTHTDBS films is therefore different from conventional layer-by-layer films, since DBS is expected to be incorporated into the PTHT chain via counterion exchange. As a consequence, the conjugation length could also be controlled by controlling the DBS content in the film. Further advantage of introducing DBS lies in the possibility of converting films with a high conjugation length at 115 o C within only 3 min. The luminescence and absorption spectra at low temperatures show a very intense well-resolved vibronic structure. We also demonstrated the band-gap control of PPV films with a possible heterostructure formation.
INTRODUCTION The recent discovery [1] of the extremely rapid thermal conversion process of poly(pphenylene vinylene) (PPV) by incorporation of dodecylbenzene sulfonic counterion (DBS) has opened up a number of new possibilities to molecularly engineer superstructures with improved properties. The main advantage of this novel procedure is that thermal conversion of PPV may be realized at considerably lower temperatures (80-100 oC) than those conventionally used (> 200 o C) [2-4], within a very short time (down to 3 minutes) and under ambient conditions. Incorporation of DBS has been used to improve processability of the PPV-precursor to fabricate multilayer Langmuir-Blodgett (LB) films [5] and spin-cast techniques [1]. The resulting PPV films possess less defects compared to films converted at high temperatures, owing to the absence of carbonyl-related defects, thus leading to a dramatic improvement in quantum efficiency of PPV when the conversion temperature is decreased form 230 to 80 oC. In addition, the conjugation length could also be controlled by varying the immersion time in SA or DBS concentration in the film in spin-coating procedure, raising the possibility that the band gap between LUMO and HOMO states can be varied along the PPV film. Besides the possibility of band-gap engineering, confinement structures (such as asymmetric lather type or “V-type” structures) may lead to distinct results, as for example the transport of the excited or injected carriers to the proximity of the substrate or to the film surface, improving the effective quantum efficiency of the active material. JJ8.14.1 Downloaded from https:/www.cambridge.org/core. University of A
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