2-Arylvinylpyrimidines versus 4-arylvinylpyrimidines: synthesis and comparison of the optical properties.

International audienceCondensation of donor-substituted aldehydes on methylpyrimidine led to two series of fluorescent molecules depending on the position of the methyl group. Whereas highly emissive 4-arylvinylpyrimidine derivatives are well-known, this is the first example of fluorescent 2-arylvinylpyrimidine compounds. The optical properties of the two families have been thoroughly compared. Whereas the series derived from 2-methylpyrimidine exhibit a blue shift in absorption and emission in comparison with 4-arylvinylpyrimidine, the influence of the position is less predictable on the fluorescence quantum yield. These compounds also exhibit halochromism: when adding acid, a bathotromic shift is observed in absorption whereas an increase of the fluorescence intensity which is red-shifted except for amino derivatives (a progressive quench of emission is observed in these cases). An emission solvatochromism study has shown that a higher intramolecular charge transfer seems to occur in 2-arylvinylpyrimidines than in 4-arylvinylpyrimidines

Two-Photon Absorption in a Conformationally Twisted D-π-A Oligomer : A Synergic Photosensitizing Approach for Multiphoton Lithography

International audienceA comparative study of the linear and nonlinear optical properties of a novel triphenylamine–pyrimidine alternated oligomer and its corresponding V-shaped quadrupolar monomer is presented. Both chromophores strikingly exhibit the same spectral shape when considering their respective one- and two-photon absorption spectra. This effect was attributed to a weak interchromophore coupling within the oligomer which exhibits a highly distorted geometry resulting in a strong reduction of the effective conjugation length. The recursive implementation of nine monomers into a three-dimensional architecture leads however to a cooperative enhancement of the two-photon absorption (2PA) cross-section with a δMAX of 5093 GM at 800 nm. This very high 2PA ability has been oriented to improve the two-photon induced polymerization efficiency of a bicomponent photoinitiator system implying a hexaarylbiimidazole used as a H-abstractor and an aliphatic amine used as a H-donor. The photosensitizing mechanism is investigated and we clearly show that the intrinsic photoinitiation efficiency of the oligomer is increased by a factor 3 as compared to its corresponding monomer. We therefore demonstrate that such a two-photon sensitizing strategy leads to a synergy effect combining a higher photoinitiation reactivity and a very large two-photon absorption cross-section

Anisyl and ferrocenyl adducts of methylenepyran-containing β-diketone: Synthesis, spectral, structural, and redox properties

International audienceWittig reaction between the in situ generated [2,6-diphenyl-4H-pyran-4-yl phosphorane and methyl 4-formylbenzoate afforded the methyl 4-[(2,6-diphenyl-4H-pyran-4-ylidene)methyl]benzoate precursor 2 in 75% yield. The anisyl and ferrocenyl adducts of methylenepyran-containing β-diketones 3 and 4, respectively, were prepared from the base-catalyzed Claisen condensation reaction between precursor 2 and 4-methoxyacetophenone or acetylferrocene, using t-BuO−K+ as basic initiator. Both β-diketones 3 and 4 were isolated as an orange and dark-red crystalline solids in 50% yield, respectively. The acetyl derivative 6, 1-acetyl-1′-methylenepyranyl-ferrocene, was synthesized following a classical Friedel-Crafts acylation reaction of the parent ferrocenylmethylenepyran 5, and isolated in 61% yield as a red microcrystalline powder. The condensation reaction between the electron-rich acetyl complex 6 and acetyl acetate, using lithium diisopropylamide as the active base initiator, provided the ferrocenylmethylenepyran-containing β-diketone, 1-(1,3-dioxobutyl)-1′-[(2,6-diphenyl-4H-pyran-4-ylidene)methyl] ferrocene 7, isolated in 20% yield as an orange powder. The composition and identity of the new compounds 2-4, 6 and 7 are supported by elemental analysis, FT-IR, one- and two-dimensional 1H and 13C NMR spectral data and mass spectrometry. Additionally, the molecular structures of compounds 2, 4 and 6 were ascertained by single-crystal X-ray diffraction study. FT-IR and NMR spectral data indicate that both β-diketones 3 and 4 do solely exist as their keto-enol tautomeric form in solution and in the solid state, whereas a mixture of keto-enol and β-diketone tautomers in a 73:27 spectroscopic ratio was observed for 7. In the three cases, enolization takes place exclusively away from the anisyl or ferrocenyl group with formation of a six-membered pseudo-aromatic keto-enol ring, confirmed by the crystal structure of 4. Cyclic voltammetric measurements revealed that all the compounds undergo a single one-electron oxidation, localized presumably at the methylenepyran unit. This first oxidation generates a radical cation that undergoes an intermolecular C-C bond coupling to form the corresponding dimer. Anodically shifted to the first oxidation, cyclovoltammogram of 4 exhibits one reversible two-electron oxidation while that of 6 and 7 present two successive reversible one-electron oxidations, attributed in the three cases to the ferrocenyl fragment of the dimer

Tripodal molecules with triphenylamine core, diazine peripheral groups and extended π-conjugated linkers

International audienceA series of five octupolar molecules with central triphenylamine donor and peripheral diazine electron-withdrawing groups has been prepared. These structures possess extended π-spacer comprising multiple bonds in a combination with 1,4-phenylene and 2,5-thienylene subunits. Starting from tris(4-ethynylphenyl)amine, the key step in the preparation of the chromophores involves triple Sonogashira cross-coupling reaction. The photophysical properties of the compounds are described. A strong positive emission solvatochromism, typical for dyes featuring Intramolecular Charge Transfer (ICT), is observed, two-photon absorption (2PA) properties were also measured. Linear and nonlinear optical properties as well as electronic properties measured by cyclic voltametry and supported by DFT calculation were used to elucidate structure-property relationship

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

Synthesis, photophysics and nonlinear optical properties of stilbenoid pyrimidine-based dyes bearing methylenepyran donor groups.

International audienceThe nonlinear properties and the photophysical behavior of two π-conjugated chromophores that incorporate an electron-deficient pyrimidine core (A) and γ-methylenepyrans as terminal donor (D) groups have been thoroughly investigated. Both dipolar and quadrupolar branching strategies are explored and rationalized on the basis of the Frenkel exciton model. Even though a cooperative effect is clearly observed if the dimensionality is increased, the nonlinear optical (NLO) response of this series is moderate if one considers the nature of the D/A couple and the size of the chromophores (as measured by the number of π electrons). This effect was attributed to a disruption in the electronic conjugation within the dyes' scaffold for which the geometry deviates from planarity owing to a noticeable twisting of the pyranylidene end-groups. This latter structural parameter also has a strong influence on the excited-state dynamics, which leads to a very efficient fluorescence quenching

Synthesis and Photophysical Studies of a Series of Quinazoline Chromophores

International audienceThe synthesis of a series of push-pull arylvinyl (styryl), aryl, and arylethynyl quinazoline derivatives by means of different straightforward protocols is reported. The photophysical properties of the compounds are described. The preparation of arylvinylquinazolines was performed by aldol condensation of the appropriate methylquinazoline and functionalized benzaldehyde. Suzuki and Sonogashira cross-coupling reactions were used to prepare the aryl and arylethynyl compounds, respectively, starting from chloroquinazolines. Optical studies revealed that all of the compounds reported here behave in a way similar to that of their pyrimidine counterparts, with absorption bands in the UV or visible region and the emission of green light upon irradiation. Large red shifts were observed in the fluorescence emission maxima upon increasing the solvent polarity. This strong emission solvatochromism suggests the formation of an intramolecular charge-separated emitting state. The materials can be easily and reversibly protonated at the nitrogen atoms of the heterocyclic ring, and this causes dramatic color changes. This phenomenon opens up the possibility of developing colorimetric pH sensors that can be efficiently modified a posteriori for specific applications

The arylvinylpyrimidine scaffold: a tunable platform for luminescent and optical materials

International audienceThe incorporation of electron-withdrawing pyrimidine rings within π-extended systems allows access to a wide variety of fluorescent push-pull molecules that display emission properties highly sensitive to external stimuli. A suitable design of these compounds leads to interesting materials for a variety of optoelectronic applications. In this context, a vast number of arylvinylpyrimidine-based chromophores have been extensively studied during the last two decades. Along with the main synthetic pathways, this review summarizes the photophysical features of these active compounds having great potential and their most important applications as sensors and luminescence materials

4‐substituted push‐pull quinazoline chromophores with extended π‐conjugated linker

International audienceA series of four push‐pull compounds based on a 4‐phenylquinazoline scaffold were designed. Three of these compounds exhibit dual state emission with intense fluorescence in solution and solid state. Their emission properties are sensible to environement stimuli with intense emission solvatochromism and halochromism. In case of methoxy derivative, both neutral and protonated form are luminescent and white light emission can be observed by controlled partial protonation

Luminescence Behavior of Protonated Methoxy-Substituted Diazine Derivatives: Towards White Light Emission

acknowledge the HPC resources of CINES and of IDRIS under the allocations 2016-[x2016080649] made by GENCI (Grand Equipment National de Calcul Intensif)International audienceWhite light emitting diodes (WOLEDs) are an efficient alternative to conventional lighting sources. Nevertheless, approaches to obtain WOLEDs still require complex processes that lead to high costs. In this sense, the use of a single emitting material that can take two forms of complementary emitting colors has emerged as a new strategy for the fabrication of WOLEDs. In this paper we describe the luminescent behavior upon protonation of a series of D-π-A push-pull molecules based on a methoxyphenyl or methoxynaphthyl donor unit and a diazine acceptor unit with different π-bridges. The effect of protonation on the emission properties depends on the nature of the diazine ring. The addition of trifluoroacetic acid (TFA) to pyrazine and quinoxaline derivatives led to quenching of the fluorescence whereas pyrimidine derivatives remained luminescent after protonation, which prompted a color change in the emission due to the appearance of a new red-shifted band in the spectra. These results were rationalized with the help of TD-TFT calculations. White photoluminescence could be obtained in solution by the controlled protonation of some pyrimidines, which resulted in the formation of an orange emissive acidified form. This phenomenon opens up the possibility of exploiting these materials for the fabrication of WOLEDs