Highly Oriented Langmuir−Blodgett Films of Poly(p-phenylenevinylene) Using a Long Chain Sulfonic Counterion

Abstract

Langmuir-Blodgett (LB) films of a poly(p-phenylenevinylene) (PPV) precursor were prepared using an amphiphilic precursor, poly(xylylidenetetrahydrothiophenium chloride) (PTHT), where the counterion chloride was replaced by a long chain dodecylbenzenesulfonate (DBS) ion. Stable PTHT-DBS monolayers were transferred onto quartz substrates in the form of LB films. Using DBS allowed PPV films to be converted under atmospheric pressure at temperatures as low as 80 °C, with conjugation length and optical properties better than for standard films converted at temperatures above 200 °C under controlled atmospheres. These LB-PPV films are highly anisotropic as demonstrated by linear dichroism experiments using linearly polarized optical absorption and emission. The dichroic ratio between the intensity of the emitted light parallel and perpendicular to the dipping direction was ca. 17, which is much higher than the dichroic ratio of 3.6 found in the polarized absorption experiment. This difference indicates an efficient excitation transfer between the low conjugated segments (disordered) and the highly conjugated (ordered) ones after excitation.

Substrate/semiconductor interface effects on the emission efficiency of luminescent polymers

“…The main difference in PL intensity between the two annealing temperatures occurs at 300 K for the thinnest films, with 5 and 25 bilayers. This is consistent with previous findings 14 where oxidative processes (mainly formation of C@O groups) were attributed to emission quenching centers for 20-bilayer LBL films. Unexpectedly, the maximum PL quenching of the bulk films is almost independent of the concentration of quenching centers.…”

“…However, it is still useful for fundamental studies, especially because it is amenable to form LBL films with high control of film thickness. 14 PPV films can be processed via soluble precursor polyelectrolyte poly(xylylidene tetrahydro-thiophenium chloride) (PTHT) and thermally converted at moderate temperatures ($200-300 C). 15 The thermal elimination at high temperature of the lateral groups, tetrahydro-thiophenium, of PTHT causes undesired consequences for the PPV matrix.…”

“…Defects such as carbonyl groups reduce substantially the photo-and electroluminescence efficiency of the active layer. This difficulty has been circumvented with an alternative synthesis route, 14 in which dodecylbenzenesulfonate (DBS) was used as the PTHT counterion during the LBL film fabrication. With this new route, thermal conversion into PPV may be performed at significantly lower temperatures, e.g., 110 C, also reducing the oxidation-induced defects.…”

Influência da espessura nas propriedades de absorção e emissão e na morfologia de filmes automontados de poli(p-fenileno vinileno

“…A razão dicróica (d = A // /A ⊥ ) calculada em 440 nm diminui de 2,28 para 1,12 quando a espessura do filme aumenta de 5 para 75 camadas, como pode ser visto na Tabela 2. Comparando com filmes altamente organizados, particularmente os obtidos pela técnica Langmuir-Blodgett, 24 os filmes SA-PPV com 75 camadas apresentam uma razão dicróica 3,2 vezes menor. Este dado mostra que estes filmes são comparativamente pouco ordenados confirmando a hipótese de que, com o aumento do número de camadas, há um crescimento desordenado (ou randômico) do filme, propriedade intrínseca da técnica de automontagem.…”

Energy transfer in a multilayer film via spin self-assembly

“…Recently, Marletta reported that PPV precursor, where the counter chloride was replaced by a long chain DBS ion, could be rapidly converted to PPV with a long conjugation length even at a low conversion temperature, 80-100°C [18][19][20][21]. DBS-treated PPV precursor films can be formed via various methods such as Langmuir-Blodgett (LB) [19], self-assembly [19,20] and spin-coating [18], and in all three systems a rapid low conversion process was possible.…”