Isabelle Lévesque

Blue light-emitting devices from new conjugated poly(N-substituted-2,7-carbazole) derivatives

Light-emitting diodes derived from a new class of conjugated polymers, well-defined poly(N-substituted-2,7-carbazole) derivatives, are reported. Excimer-free electroluminescence in the blue range (424–432 nm) was observed. Good luminance (372 cd/m2 at 10 V) was reached in a device containing poly[N-(2-ethylhexyl)-2,7-carbazole] as the emitting material with indium tin oxide and Al as the electrodes. This high luminance value was achieved by adding ultrathin LiF layers next to the electrodes, and by using hole and electron transport molecules such as N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine and 2-(4-biphenylyl)-5(4-tert-butylphenyl)-1,3,4-oxadiazole.

Organic field effect transistors based on modified oligo-p-phenylevinylenes

We report on an organic field effect transistor device based on a modified oligomer oligo-p-phenylevinylene, 1,4-bis[4-(4-octylphenyl)styryl]-benzene. The effect of growth temperature on the morphology of the organic films and their electrical properties was investigated. Substrates coated with hexamethyldisilazane prior to organic film deposition showed improved electrical characteristics, but a negligible difference with respect to film morphology. A maximum hole mobility of μ=0.12 cm2/V s with an on–off current ratio Ion/off>106 were measured in films deposited at a substrate temperature of 150 °C.

Controlled ionochromism with polythiophenes bearing crown ether side chains

Regioregular poly(3-alkoxy-4-methylthiophene)s bearing crown ethers of different sizes (12-crown-4), PT12C4; and (15-crown-5) PT15C5) have been synthesized and their thermochromic and ionochromic behaviors investigated. These polythiophene derivatives exhibit a highly conjugated form in the solid state at room temperature (absorption maximum around 550 nm) and a less conjugated form upon heating (absorption maximum around 425 nm). In acetone or ethyl acetate ionochromic responses have been observed upon addition of some alkali metal cations. Initially, the absorption maximum is located around 425 nm (yellow) but moves to 550 nm (violet). These results indicate the formation of planar (highly conjugated) polymeric assemblies upon the addition of alkali metal cations. PT12C4 is more sensitive to sodium salts while PT15C5 gives more intense ionochromic effects with potassium salts. These effects can be explained by a more stable 2:1 complexation between a given crown ether and an appropriate alkali metal cation.

An integrated shadow-mask based on a stack of inorganic insulators for high-resolution OLEDs using evaporated or spun-on materials

Abstract While organic materials show impressive performances as electroluminescent diodes, their integration in a passive matrix to form a high-resolution display is a challenge. The anode can easily be patterned in columns prior to the deposition of organic materials, but conventional microfabrication techniques cannot be used to etch the cathode on top because organics are affected by treatments applied to photosensitive resins. We microfabricated an integrated shadow-mask with openings in rows orthogonal to the columns of the anode. The mask has an overhanging edge so that the cathode evaporated on top is discontinuous at its edges, thereby separating the diodes along rows. The mask is composed of a stack of inorganic insulators all deposited in a commercial plasma-enhanced chemical vapor deposition tool, and whose different etching rates in hydrofluoridric acid enable to obtain the overhang in one lithographic step. The process is very simple, as high resolution as microfabrication can provide, and the resulting device is less prone to short-circuits than when a lift-off photoresist is used. Pixellation is reported both from evaporated small molecules and spun-on polymers.

Rigid organic nanotubes obtained from phenylene-butadiynylene macrocycles

Rigid organic nanotubes were prepared from six-membered phenylene-butadiynylene macrocycles through topochemical polymerization in the xerogel state. All six butadiyne units underwent polymerization, thus creating rigid nanotubes with six polydiacetylene chains lying parallel, one relative to each other.

Layered graphitic materials from a molecular precursor

A layered graphitic material was prepared from an alkyne-containing, reactive molecular precursor at low temperature without catalyst. The resulting nanomaterial is made of stacks of a few partially graphitized nanosheets and is soluble in common organic solvents in which it exhibits green fluorescence.

Chromism in polythiophene derivatives

Abstract Thermochromism has been observed in some polythiophene derivatives both in the solid state and in solution. These optical effects are related to a planar/non-planar transition of the conjugated backbone. Various measurements have revealed a strong dependence of these chromic properties upon the nature, the position and the conformation of the substituents. These results seem to indicate that the twisting of the main chain could be driven by order-disorder “transitions” of the side chains. Order-disorder side-chain transition can be induced from different stimuli and this concept has led to the development of novel ionochromic polymers. Similar phenomena could also be induced through side chain cis-trans photoisomerisation (photochromism) , or by side chains that would possess some affinity to chemical or biochemical molecules (affinity chromism) .

Electrochemical molecular recognition by thin films of ether-substituted polythiophenes

Abstract The electrochemical behaviour of cast films of poly(3-oligo(oxyethylene)-4-methylthiophene) is reported. These films exhibit electrochemical recognition for alkali metal cations with selectivity in the order K+>Na+>Li+.

Synthesis of a controlled three-faced PAMAM particle

We report the synthetic proof-of-concept for a three-faced particle based on a PAMAM dendrimer in which each face bears a different labile protecting group. This new strategy yields a controlled, well-defined and monodisperse dendrimer. To achieve this, a tri-orthogonal strategy was employed through Sonogashira coupling and Cu(I)-catalyzed Huisgen [2 + 3] dipolar cycloaddition (“click” chemistry). The afforded dendrimer is well suited for further development in a variety of fields as each branch can be addressed individually for functionalization.

Use of a patient decision aid for prenatal screening for Down syndrome: what do pregnant women say?

BackgroundPatient decision aids (PtDAs) help people make difficult, values-sensitive decisions. Prenatal screening for assessing the risk of genetic conditions in the fetus is one such decision and patient decision aids are rarely used in this clinical context. We sought to identify factors influencing pregnant women’s use of a patient decision aid for deciding about prenatal screening for Down syndrome (DS).MethodsThis qualitative study was embedded in a sequential mixed-methods research program whose main aim is to implement shared decision-making (SDM) in the context of prenatal screening for DS in the province of Quebec, Canada. We planned to recruit a purposive sample of 45 pregnant women with low-risk pregnancy consulting for prenatal care at three clinical sites. Participating women watched a video depicting a prenatal care follow-up during which a pregnant woman, her partner and a health professional used a PtDA to decide about prenatal screening for DS. The women were then interviewed about factors that would influence the use of this PtDA using questions based on the Theoretical Domains Framework (TDF). We performed content analysis of transcribed verbatim interviews.ResultsOut of 216 eligible women, 100 agreed to participate (46% response rate) and 46 were interviewed. Regarding the type of health professional responsible for their prenatal care, 19 participants (41%) reported having made a decision about prenatal screening for DS with an obstetrician-gynecologist, 13 (28%) with a midwife, 12 (26%) with a family physician, and two (4%) decided on their own. We identified 54 factors that were mapped onto nine of the 12 TDF domains. The three most frequently-mentioned were: opinion of the pregnant woman’s partner (n = 33, 72%), presentation of the PtDA by health professional and a discussion (n = 27, 72%), and not having encountered a PtDA (n = 26, 57%).ConclusionThis study allowed us to identify factors influencing pregnant women’s use of a PtDA for prenatal screening for DS. Use of a PtDA by health professionals and patients is one step in providing the needed decision support and our study results will allow us to design an effective implementation strategy for PtDAs for prenatal screening for DS.