Françoise Robin-Le Guen

Synthesis and Photophysical Investigation of a Series of Push–Pull Arylvinyldiazine Chromophores

A new series of push-pull arylvinyldiazines has been efficiently prepared by aldol condensation between the appropriate methyldiazine and aromatic aldehyde. The optical absorption and emission properties of these chromophores were studied in different solvents and media. These compounds act as polarity sensors with a strong positive emission solvatochromism. This behavior suggests a highly polar emitting state, which is characteristic of compounds that undergo an internal charge transfer upon excitation. These molecules also exhibit halochromic properties and are potential colorimetric and luminescence pH sensors. The second-order nonlinear properties have been investigated for some of the compounds, and large and positive μβ are obtained, in particular, for pyrimidine derivatives.

Synthesis and photophysical studies of a series of quinazoline chromophores.

The 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.

Donor–linker–acceptor (D–π–A) diazine chromophores with extended π-conjugated cores: synthesis, photophysical and second order nonlinear optical properties

The synthesis of a series of push–pull pyrimidine and quinoxaline chromophores with extended π-conjugated cores is reported. Starting from a bromoarylvinyldiazine derivative, the key step in the preparation of the chromophores consists of a Sonogashira cross-coupling reaction. The photophysical properties of the compounds are described. A strong positive emission solvatochromism, typical for dyes presenting Intramolecular Charge Transfer (ICT), is observed, in particular for amino substituted derivatives with larger solvatochromic range than known analogous chromophores with smaller π-conjugated cores. The second order non linear optical (NLO) properties were investigated for some of the compounds and a comparison with the NLO responses of already described diazine chromophores exhibits a significant enhancement of the NLO properties by extension of the π-conjugated core.

Reactivity of carbanions of Fischer-type carbene complexes with pyrylium salts. Synthesis and characterization of new γ-methylenepyran carbene complexes via an addition–oxidation–deprotonation process

The condensation reaction between γ-unsubstituted pyrylium salts and carbanions of Fischer-type carbene complexes allowed the synthesis of new γ-methylenepyran carbene complexes. NMR data, single crystal X-ray analysis, and DFT calculations suggest that these complexes have a partial pyrylium character due to the π electron-accepting ability of the carbenic fragment and to the electron-releasing properties of the methylenepyran part.

Two-photon absorption in a conformationally twisted D–π–A oligomer: a synergic photosensitizing approach for multiphoton lithography

A 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.

Synthesis, photovoltaic performances and TD-DFT modeling of push–pull diacetylide platinum complexes in TiO2 based dye-sensitized solar cells

In this joint experimental-theoretical work, we present the synthesis and optical and electrochemical characterization of five new bis-acetylide platinum complex dyes end capped with diphenylpyranylidene moieties, as well as their performances in dye-sensitized solar cells (DSCs). Theoretical calculations relying on Time-Dependent Density Functional Theory (TD-DFT) and a range-separated hybrid show a very good match with experimental data and allow us to quantify the charge-transfer character of each compound. The photoconversion efficiency obtained reaches 4.7% for 8e (see TOC Graphic) with the tri-thiophene segment, which is among the highest efficiencies reported for platinum complexes in DSCs.

Dipolar NLO Chromophores Bearing Diazine Rings as π-Conjugated Linkers

The synthesis of a series of push-pull derivatives bearing triphenylamine electron-donating group, cyclopenta[c]thiophen-4,6-dione electron acceptor and various π-linkers including (hetero)aromatic fragments is reported. All target chromophores with systematically varied π-linker structure were further investigated by electrochemistry, absorption measurements, and EFISH experiments in conjunction with DFT calculations. Based on electrochemical and photophysical measurements, when a polarizable 2,5-thienylene moiety is embedded into the chromophore π-backbone the highest intramolecular charge transfer (ICT) is observed. Benzene, pyrimidine, and pyridazine derivatives exhibit lower polarizability and extent of the ICT across these π-linkers. The elongation of the π-conjugated system via additional ethenylene linker results in a significant reduction of the HOMO-LUMO gap and an enhancement of the NLO response. Whereas it does not significantly influence electrochemical and linear optical properties, the orientation of the pyrimidine ring seems to be a key parameter on the μβ value due to significant variation of the dipolar moment (μ) value. In 2a and 2c, pyrimidine is oriented to behave as an acceptor and thus generate dipolar molecule with μ above 5 D, whereas in 2b and 2d ground state dipole moment is significantly reduced. This study seems to indicate a high aromaticity of pyrimidine and pyridazine derivatives, close to the benzene analogues and significantly higher than thiophene analogues.

Reactivity of carbanions of Fischer-type carbene complexes with pyrylium salts. Synthesis of new γ-methylenepyran carbene complexes via an addition-oxidation-deprotonation process

Abstract The condensation reaction between γ-unsubstituted pyrylium salts and carbanions of Fischer-type carbene complexes allowed the synthesis of new γ-methylenepyran carbene complexes. 13C NMR data and single cristal X-ray analysis suggest a delocalisation of the oxygene lone pair of the heterocycle.

Protonable pyrimidine derivative for white light emission

White photoluminescence both in solution and the solid-state was obtained by the controlled protonation of a blue emitting 4,6-bis(arylvinyl)pyrimidine, which resulted in the formation of an orange emissive acidified form. This dye has potential applications in the fabrication of white OLEDs based on only one material.

SYNTHESIS, STRUCTURE AND REACTIVITY OF ACETYLENIC CO2(CO)6 PYRYLIUM SALTS.ELECTRONIC INFLUENCE OF THE CO2(CO)6 ACETYLENIC FRAGMENT

Abstract The formation of new pyrylium salts bearing in the γ position an acetylenic Co2(CO)6 fragment is described. X-ray analysis showed that the γ carbon of the pyrylium ring does not interact with a cobalt atom. However, IR values, relating to the carbonyl stretching band, suggested that a part of the positive charge is delocalized on the cluster core. Finally, the reactivity of these cationic complexes towards nucleophiles is reported.