Bertrand Caro

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.

4-Benchrotrenyl Pyrylium Salts as Protein Organometallic Labelling Reagents

Abstract Pyrylium ions are useful reagents to selectively modify the amino group of protein lysine residues. This property was exploited here to label proteins with chromium tricarbonyl complexes in the form of 4-benchrotrenyl pyridinium ions. Kinetic studies of the reaction of a series of benchrotrenyl pyrylium salts with water and n-butylamine were performed and revealed that the overall reactivity of these compounds was highly dependent on their substitution pattern. These compounds could find application in protein X-ray crystallography.

Synthesis of electron donor–acceptor polyunsaturated methylenepyran Fischer type carbene complexes: dynamic 1H-NMR study and solvatochromic properties

Condensation of α and γ methylenepyran aldehydes with the Fischer carbene complexes (CO)5MC(OCH3)Me (M=Cr, W) or (CO)5WC(OCH3)CHCH–CH3 in the presence of ClSiMe3/NEt3 yield donor acceptor complexes, in which the electron donating group is connected to the organometallic accepting group by a conjugated ethylenic spacer. 1H- and 13C-NMR studies, suggest that the carbene fragment and the unsaturated chain lie in the same plan, allowing a mesomeric interaction between the oxygen atom of the heterocycle and the metal via the spacer. The positive solvatochromism of the molecules obtained is reported.

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.

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.

Diacétylation d'ethyléniques du benzène chrometricarbonyle. Voie d'accès aux sels de pyrylium γ-benchrotréniques. Analyse structurale aux rayons X et influence electronique inhabituelle du groupement Cr(CO)3

Abstract γ-Benchrotrenic pyrylium salts synthesis is reported. N.M.R. data and theoretical calculations suggest that the Cr(CO) 3 fragment is electron donating towards the pyrylium ring. X-ray structure of the complexe pyrylium salt indicates that the electron transfer does not implicate the chromium d orbitals.

FT-IR observation of covalent labelling of lysozyme crystals by organometallic complexes of transition metals

Electrophilic complexes of iron and chromium which have been reported to react with proteins in solution have been reacted with hen-egg white lysozyme (HEWL) in both the solution and crystal phases under similar pH and buffer conditions. This work was carried out with a view to developing novel side-chain selective heavy metal derivatives for protein X-ray crystallographic studies. Reaction of HEWL with a tricarbonyldienyliron cation (1) in aqueous solution led to modification of the sole histidine residue with concurrent reversible modification of other protein residues. Reaction of (1) with crystalline HEWL showed no covalent binding and only a build up of a hydrolysis product in the water channels of the crystal was observed. Reactions with a series of tricarbonylarylchromium pyrylium salts (2) led to the formation of stable covalent HEWL derivatives in solution. Chromatographic and IR spectroscopic studies showed that binding took place specifically at the epsilon-amino group of lysine residues to give a series of mono- and di-substituted products. When crystals of HEWL were soaked with the chromium reagents covalent binding to some of the lysine residues was also observed. In contrast, HEWL crystals which had their lysine side chains disabled did not bind any of the chromium reagents.

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.

Diferrocenylpyrylium salts and electron rich bispyran from oxidative coupling of ferrocenylpyran. Example of redox systems switched by proton transfer

Electro or chemical oxidation of ferrocenylmethylenepyran gave an ethanediferrocenylbispyrylium salt through the dimerization of a ferrocenylpyran radical-cation (C–C bond making). Electro or chemical reduction gave back the ferrocenylmethylenepyran (C–C bond breaking). This electrochemical reverse system constitutes an example of C–C bond making–breaking process in a metallocenyl series with rather high stability. DFT calculations and electrochemical studies were carried out in order to determine the electronic structure of the radical cation intermediate, the role of the ferrocenyl groups and the mechanism of the C–C bond making and C–C bond breaking processes. Reversible deprotonation of the ethanediferrocenylbispyrylium salt afforded an extended diferrocenylbismethylenepyran, which was subsequently reversibly oxidized to an ethenediferrocenylbispyrylium salt. X-Ray crystallographic data of diferrocenylbismethylenepyran and ethenediferrocenylbispyrylium salt allowed to determine the molecular movements, which come with the electron transfer (ET). A comparison with the behavior of the corresponding isoelectronic bisdithiafulvenes (extended TTF) and bisdithiolium salts was made.