TUNING THE PHOTOPHYSICAL PROPERTIES OF PUSH-PULL AZAHETEROCYCLIC CHROMOPHORES BY PROTONATION: TOWARDS WHITE LIGHT EMISSION

Conjugated push-pull molecules that incorporate nitrogen heterocycles as electronwithdrawing units are interesting materials because of their luminescence properties. These chromophores can be easily and reversibly protonated at the nitrogen atom of the heterocyclic ring and this can cause dramatic color changes. White and multi-color photoluminescence both in solution and in the solid state can be obtained by an accurate control of the amount of acid [1-6]. Thus, with a suitable design these compounds have potential applications in the development of colorimetric pH sensors and the fabrication of OLEDs based on only one material. We provide here a brief overview of our collaborative efforts made in this area with pyrimidine, pyridine and (iso)quinoline derivatives

Cromóforos dador-aceptor basados en azaheterociclos como emisores de luz blanca

There is an increasing interest in conjugated push-pull chromophores that incorporate nitrogen heterocycles as electron-withdrawing units because their photophysical properties are highly sensitive to external stimuli. In this respect, reversible proto-nation causes dramatic color changes, whereas the emission is often quenched. Nevertheless, in some cases the presence of acid prompts the appearance of emission bands of complementary colors. Thus, white and multicolor photoluminescence both in solution and in the solid state can be obtained by the controlled protonation of the azaheterocyclic ring. With a suitable design, these compounds have potential applications in the development of colorimetric pH sensors and the fabrication of OLEDs based on one single material.Existe un gran interés en los cromóforos conjugados de tipo dador-aceptor que incorporan heterociclos nitrogenados como unidades electroatractoras debido a que sus propiedades fotofísicas son muy sensibles a diversos estímulos externos. La pro-tonación reversible provoca cambios drásticos en el color y, a menudo, una pérdida total de la emisión. Sin embargo, en algunos casos, la presencia de ácido provoca la aparición de bandas de emisión de colores complementarios. El control de la protonación permite obtener fotoluminiscencia blanca y multicolor tanto en disolución como en estado sólido. Con el diseño adecuado, estos compuestos podrían ser utilizados para desarrollar sensores colorimétricos de pH y fabricar OLEDs basados en un único material

Evaluación de la carga bacteriana del aire en centros educativos como proyecto didáctico

The present work aims to improve the scientific literacy of high school students through the evaluation of the indoor air bacterial load the classrooms of a secondary school. This activity attempts to bring students closer to scientific research, encouraging active work, and contextualizing the content discussed in the classroom as a means of meaningful learning.El presente trabajo pretende mejorar la alfabetización científica del alumnado de bachillerato a través de la evaluación de la carga bacteriana del aire en las aulas de un instituto de secundaria. Con esta actividad se intenta acercar al alumnado a la labor científica, fomentando el trabajo activo y contextualizando los contenidos tratados en el aula como medio de aprendizaje significativo. Palabras clave: proyecto de investigación, propuesta didáctica, aprendizaje significativo, aprendizaje basado en proyectos, laboratorio de educación secundaria. Assessment of indoor air bacterial load in educational centres as a didactic project Abstract: The present work aims to improve the scientific literacy of high school students through the evaluation of the bacterial load of indoor air in the classrooms of a secondary school. This activity attempts to bring students closer to scientific research, encouraging active work, and contextualizing the content discussed in the classroom as a means of meaningful learning. Keywords: research project, didactic proposal, air quality, secondary school laborator

Synthesis and Photophysical Properties of Substituted Pyrimidines

A series of pyrimidine derivatives bearing one, two or three triphenylamine/9-ethylcarbazole substituents has been synthesized by Suzuki cross-coupling reaction. All compounds showed absorption bands in the UV region and the emission of violet-blue light upon irradiation. Protonation led to quenching of the fluorescence, although some derivatives remained luminescent with the appearance of a new red-shifted band in the spectra. Accurate control of the amount of acid enabled white photoluminescence to be obtained both in solution and in solid state

Carbazole- and Triphenylamine-Substituted Pyrimidines Synthesis and Photophysical Properties

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Excited-State Intramolecular Proton Transfer in 2-(2′-Hydroxyphenyl)pyrimidines: Synthesis, Optical Properties, and Theoretical Studies

International audienceThe development of fluorescence materials with switched on/off emission has attracted great attention owing to the potential application of these materials in chemical sensing. In this work, the photophysical properties of a series of original 2-(2′hydroxyphenyl)pyrimidines were thoroughly studied. The compounds were prepared by following well-established and straightforward methodologies and showed very little or null photoluminescence both in solution and in the solid state. This absence of emission can be explained by a fast proton transfer from the OH group to the nitrogen atoms of the pyrimidine ring to yield an excited tautomer that deactivates through a nonradiative pathway. The key role of the OH group in the emission quenching was demonstrated by the preparation of 2′-unsubstituted derivatives, all of which exhibited violet or blue luminescence. Single crystals of some compounds suitable for an X-ray diffraction analysis could be obtained, which permitted us to investigate inter-and intramolecular interactions and molecular packing structures. The protonation of the pyrimidine ring by an addition of trifluoroacetic acid inhibited the excited-state intramolecular proton transfer (ESIPT) process, causing a reversible switch on fluorescence response detectable by the naked eye. This acidochromic behavior allows 2-(2′-hydroxyphenyl)pyrimidines to be used as solid-state acid−base vapor sensors and anticounterfeiting agents. Extensive density functional theory and its time-dependent counterpart calculations at the M06-2X/6-31+G** level of theory were performed to rationalize all the experimental results and understand the impact of protonation on the different optical transitions

Effect of protonation on the photophysical properties of 4-substituted and 4,7-disubstituted quinazoline push-pull chromophores

International audienceWhite-light emission from single molecular systems has attracted a great deal of attention due to their advantages over multicomponent emitters. Azaheterocyclic push-pull derivatives have been demonstrated to be white emitters by combining neutral and protonated forms in the appropriate ratio, although limited cases of white-light emission have been reported from quinazoline derivatives. Herein, we describe a series of push-pull 4-substituted and 4,7-disubstituted quinazolines that show white photoluminescence both in solution and in the solid state. All of the materials were prepared by straightforward Suzuki-Miyaura crosscoupling reactions and the compounds exhibited remarkable emission solvatochromism. In some cases the presence of acid prompted the appearance of emission bands of complementary colors. Thus, multicolor photoluminescence, including white light, could be finely tuned by the controlled protonation of the electron-deficient quinazoline ring

In Vitro Antioxidant and Pancreatic Anticancer Activity of Novel 5-Fluorouracil-Coumarin Conjugates

Molecular hybridization consists of the combination of two or more non-identical pharmacophores in a single molecule. It has emerged as a promising strategy that allows the design of molecular frameworks with enhanced activity and affinity compared to their parent drugs. In this work, two novel hybrids that combine the well-known anticancer chemotherapeutic agent 5-fluorouracil with antioxidant coumarin derivatives have been synthesized and characterized by means of a copper-catalyzed azide-alkyne cycloaddition (CuAAC). The conjugates showed good antioxidant properties and a high tendency to aggregate and form stable nanoparticles in aqueous media, with regular shape and uniform size. These materials have proven to be preferential cytotoxic agents in vitro against human pancreatic cancer cells PANC-1, with an activity superior to free 5-fluorouracil. These results open up the possibility of exploiting the synergistic combination between 5-fluorouracil and coumarin derivatives and warrant further investigation of these hybrids as promising pancreatic anticancer agents

Push-pull (iso)quinoline chromophores: synthesis, photophysical properties, and use for white light emission

International audienceThe photophysical properties of a series of conjugated push-pull (iso)quinolines were studied. The compounds were synthesized by well-established and straightforward methodologies. The materials exhibited not only emission solvatochromism in a variety of nonpolar solvents, but also tunable halochromism. Some of the compounds remained moderately luminescent after protonation and had a red emissive form, which was used to obtain white-light emission, both in solution and in thin films, by controlled protonation of the initially blue-green-emitting materials. This methodology has potential applications in the fabrication of white organic light-emitting diodes with two forms of a single emitter in equilibrium