Colorant azoïque

Résumé

thumb|L'azobenzène est la plus petite molécule de la famille des colorants azoïques Les colorants azoïques sont des composés azoïques dans lesquels le groupe azo relie deux noyaux benzéniques. Les colorants azoïques insolubles sont utilisés en teinturerie pour la teinture des fibres cellulosiques sous toutes ses formes. Ces colorants sont « incomplets » dans leur fabrication et qui est achevée au sein de la fibre en fin de teinture. Ainsi le colorant se présente d'une part sous forme de β-naphtol insoluble et d'autre part sous forme d'une base à diazoter ou d'un sel prêt à l'emploi. En teinturerie, on parle généralement de Naphtol et non de colorants azoïques insolubles. Ceci est également valable pour les marques concurrentes. Les pigments azoïques sont une famille de pigments organiques de synthèse, utilisés en peinture pour fabriquer des rouges, des jaunes, des oranges et des bruns Historique En 1859, Johann Peter Griess découvrait la réaction de diazotation, puis l

Source officielle

https://fr.wikipedia.org/wiki/Colorant_azo%C3%AFque

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Abatement of azo-dyes and bichlorophenols mediated by iron-oxides

EPFL1999

Chargement

Dyes, Radicals and Nitrous Oxide Adducts Derived from N-Heterocyclic Carbenes

Léonard Yannick Maurice Eymann

N-Heterocyclic carbenes are able to form covalent adducts with nitrous oxide (N2O) under ambient conditions. This thesis summarizes the studies of these adducts and their reactivity. A ditopic carbanionic N-heterocyclic carbene was found to react with nitrous oxide, resulting in a stable covalent adduct with two N2O groups attached to the heterocycle. Mesoionic N-heterocyclic carbenes derived from C2-arylated 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, as well as a triazolylidene, also react with N2O. Crystallographic analyses of all complexes reveal bent N2O groups, which can adopt a cis or trans configuration. Resulting complexes of imidazole- or triazole-based mesoionic carbenes and nitrous oxide can be converted into azo dyes by reaction with arenes in the presence of AlCl3 or HCl. The azo coupling can be achieved with electron-rich aromatic compounds such as mesitylene, trimethoxybenzene, azulene, or dibenzo-18-crown-6. The latter coupling reaction allows for an easy preparation of a colorimetric sensor for potassium or sodium ions. The putative intermediate of the reaction with acid, a rare diazohydroxide, has been isolated and structurally characterized. Using imidazolium compounds with two N2O groups, it is possible to prepare amine-substituted azo dyes, or dyes with two azoarene groups attached to the heterocycle. The synthesis and the characterization of a new class of neutral aminyl radicals is also reported. Monoradicals were obtained by the reduction of azoimidazolium dyes with potassium. Structural, spectroscopic and computational data suggest that the spin density is centered on one of the nitrogen atoms of the former azo group. The reduction of a dimeric dye with an octamethylbiphenylene bridge between the azo groups resulted in the formation a biradical with largely independent unpaired electrons. Both, the monoradicals and the biradical were found to display high stability in solution as well as in the solid state.

EPFL2018

Chargement

Squaraines are organic dyes showing the advantages of a simple synthesis, high absorption coefficients and tunable bandgaps from the visible to the near-infrared (NIR) region. Their molecular structure is based on a polymethine chain and a donor-acceptor-donor structure that can be easily matched to the requirements of new application fields. This thesis focuses on the synthesis of squaraine dyes absorbing beyond 1000 nm and their use in organic upconversion devices. Organic dyes are widely studied and applied in optoelectronic devices such as organic solar cells, organic photodetectors (OPDs) and organic light-emitting devices (OLEDs). However, investigations so far were mainly focused on dyes absorbing and emitting in the visible range. With increasing interest in NIR-technology for biomedical and optoelectronic applications, there is a growing demand for organic NIR dyes. Here, a systematic chemical synthesis approach is used to tune the properties of benz[cd]indole substituted squaraine dyes. The donor part of the dye is modified by introducing Ï-conjugated substituents that increase the donor strength and enlarge the Ï-system. Additionally, a stronger acceptor part is introduced. A series of eight dyes is synthesized and characterized. The absorption maxima show bathochromic shifts with increasing conjugation, increasing donor strength and increasing acceptor strength. The beneficial properties of the NIR-absorbing squaraine dyes are demonstrated in organic upconversion devices with sensitivity beyond 1000 nm. The device is composed of a NIR-absorbing OPD possessing an external quantum efficiency of around 80% in the reverse bias and a visible OLED. The upconversion device converts NIR light into visible light without the need of intermediate electronics, allowing for direct NIR imaging. The organic semiconducting layers of the device stack absorb very little in the visible range. Combined with an optimized semitransparent metal top electrode, a device with an average visible transmittance of 65% is achieved. The advantages of visible transparent upconversion devices can be exploited e.g. in window-integrated electronic circuits. Another major benefit of organic electronics is the possibility to fabricate devices from solution, allowing low-cost and large-area production on flexible substrates. Here, the NIR-absorbing squaraine dye is used in upconversion devices consisting of five solution-processed layers. As emitting part, a fluorescent copolymer (super yellow)-based OLED or light-emitting electrochemical cell (LEC) is investigated. The solution-processed upconversion device converts NIR light with a wavelength of 980 nm efficiently to yellow light with a wavelength of around 575 nm, exhibiting a low turn-on voltage of 2.7 V. Replacing the OLED by a LEC allows for eliminating the sensitive calcium layer that acts as electron-injection layer. Due to the presence of ions, the LEC-based device shows a dynamic behavior, which is characterized in detail. A great deal of progress has been made with upconversion devices over the last years, but a number of challenges must be resolved to finally transform present-day prototype NIR imagers into a technology. Here, I address some of the scientific opportunities and challenges, including upconverters with sensitivity beyond 1000 nm, and visibly transparent and solution-processed devices with a narrow spectral response in the NIR.

EPFL2021

Chargement

EPFL2021

Dyes, Radicals and Nitrous Oxide Adducts Derived from N-Heterocyclic Carbenes

Léonard Yannick Maurice Eymann

EPFL2018