Coumarin

Summary

Coumarin (ˈkuːmərɪn) or 2H-chromen-2-one is an aromatic organic chemical compound with formula . Its molecule can be described as a benzene molecule with two adjacent hydrogen atoms replaced by an unsaturated lactone ring , forming a second six-membered heterocycle that shares two carbons with the benzene ring. It belongs to the benzopyrone chemical class and considered as a lactone. Coumarin is a colorless crystalline solid with a sweet odor resembling the scent of vanilla and a bitter taste. It is found in many plants, where it may serve as a chemical defense against predators. By inhibiting synthesis of vitamin K, a related compound is used as the prescription drug warfarin – an anticoagulant – to inhibit formation of blood clots, deep vein thrombosis, and pulmonary embolism. Etymology Coumarin is derived from coumarou, the French word for the tonka bean. The word tonka for the tonka bean is taken from the Galibi (Car

Official source

https://en.wikipedia.org/wiki/Coumarin

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From Luminescent Lanthanide Complexes to Color Reproduction and Optical Document Security with Invisible Luminescent Inks

Julien Alexandre Andres

The present thesis deals with luminescent compounds based on lanthanide complexes that are suitable for color reproduction and optical document security with invisible luminescent inks. This thesis is divided in two distinct fields: chemistry, which produces luminescent lanthanide complexes, and color science, which was required to characterize luminescent colors and use them for color reproduction and optical document security. Concerning luminescent lanthanide complexes, the investigation is focused on the derivatization of dipicolinic acid. A modification of the carboxylate coordinating moiety of the ligand is first undertaken in order to synthesize phosphorylated ligands, which often show interesting variations of the properties of the complexes among related structures. On another hand, a derivatization of the ligand by grafting a polyoxyethylene side chain with a terminal chromophore at the para position on the pyridine core of dipicolinic acid is carried out. The ability of this chromophore to act as a sensitizer for the distant lanthanide ion coordinated on the dipicolinate moiety is investigated. A series of coumarin fluorophores are tested as sensitizers and the best coumarin is then used to further examine the mechanisms of the sensitization of the lanthanide ion, for example by shortening the polyoxyethylene pendent and thus modifying the distance between the sensitizer and the lanthanide ion. The parent europium and terbium dipicolinate complexes are then used as red emitting and green emitting luminescent dyes in invisible luminescent inks together with a blue luminescent ink. An ink spreading enhanced spectral Neugebauer prediction model is used to predict the spectral radiant emittance of any combination of the luminescent inks. The good prediction accuracy of the model is then related to the photophysical properties of the luminescent inks, which are shown to be unquenched by superposition with the other inks. This trichromic system is finally used to reproduce luminescent color halftone images visible under UV light by relying on a gamut mapping algorithm and on the spectral prediction model. In a final part, a new spectral prediction model for transmittances and reflectances is developed. It is then used for building a backlighting model where the backlight source is a luminescent emission under UV light from printed luminescent inks, and where the backlit colors are obtained by the transmission of the backlight source through color halftones printed with classical cyan, magenta and yellow inks on the other side of the same substrate. Luminescent backlit color images can then be created, which produces a new security feature for optical document security combining recto classical images under normal light, with verso luminescent images and recto luminescent backlit images under UV excitation.

EPFL2012

A series of lanthanide complexes Ln(dpxCy)(3) have been synthesised. The ligands are composed of a coordinating dipicolinic acid backbone decorated with a polyoxyethylene arm fitted with a coumarin moiety at its extremity. The nature of the coumarin as well as the length of the linker have been varied. Upon excitation at 320 nm, the coumarin exclusively acts as an antenna while the dipicolinic acid core is not excited. Upon excitation below 300 nm, both parts are excited. With europium as a metal centre, the relaxation of the europium ion (intrinsic quantum yield Phi(Eu)(Eu) and radiative lifetime tau(r)) is constant for all the studied ligands. Therefore, the observed differences in overall quantum yield (Phi(Eu)(L)) in such systems come exclusively from the variation of the terminal coumarin. The overall quantum yields of the studied complexes are low (Phi(Eu)(L) < 2% in aqueous solution). In order to rationalise the mechanism of the energy transfer and to improve the sensitisation efficiency (eta(sens)), the distance between the coumarin sensitiser and the lanthanide centre was explored in solution and compared to the solid state. In the solid state, a dramatic effect was confirmed, with an improvement of 80% in the quantum yield Phi(Eu)(L) for short linkers ((-CH2CH2O-)(n) with n = 1 compared to n = 3). By monitoring the lifetime decay of the excited state of the lanthanide cation with nanosecond vs. microsecond time-resolved spectroscopy at low temperature, the sensitisation of the lanthanide ions by coumarin derivatives was demonstrated to mainly occur through the singlet excited state of the coumarin and not via the usual triplet pathway. No evidence of a different behaviour at room temperature was found by transient triplet-triplet absorption spectroscopy.

Royal Society of Chemistry2013

A para-poly(oxyethylene) dipicolinic acid derivative coupled to methylumbelliferone was synthesized and used as a ligand for coordination with europium ions. Characterization of the complex by mass spectrometry and spectrophotometry was performed in aqueous solution and points to the formation of the 1:3 Eu/L complex. Physicochemical properties are close to those of already reported dipicolinato complexes, confirming that the presence of a coumarin chromophore does not interfere with complex formation. Photophysical measurements result in observed lifetimes of 1.4 ms and intrinsic quantum yields, Phi(Eu)(Eu), ranging from 33 to 50% (depending on the solvent used). Selective excitation can be performed either mostly on the dipicolinate (DPA) backbone (at 280 nm) or exclusively on the coupled coumarin chromophore in the near visible range (320 nm). Despite the spatial distance between the antenna and the lanthanide ion, europium emission was observed upon 320 nm excitation together with the coumarin emission. The different sensitization pathways have been explored and rationalized. Finally, the complex has been used to probe the ratio of a binary mixture of solvent, establishing the potential interest of this new class of ligands in many fields of research, from photophysics to applied chemistry.

Wiley-Blackwell2010

From Luminescent Lanthanide Complexes to Color Reproduction and Optical Document Security with Invisible Luminescent Inks

Julien Alexandre Andres

EPFL2012