Jean-Hubert Olivier

Luminescent ionic liquid crystals from self-assembled BODIPY disulfonate and imidazolium frameworks

A series of modular mesogenic salts based on the combination of anionic 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (F-BODIPY) 2,6-disulfonate dyes and trialkoxybenzyl-functionalised imidazolium cations has been designed and synthesised. Each salt contains a rigid dianionic BODIPY core associated with two imidazolium cations functionalised by 1,2,3-trialkoxybenzyl (alkyl=n-C(8), n-C(12) or n-C(16)) units or, in one case, with imidazolium cations functionalised by a trialkylgallate (3,4,5-trialkoxybenzoate) unit in which the 3,5-dialkyl groups are terminated with a polymerisable acrylate entity. All these compounds were highly fluorescent in solution with quantum yields ranging from 54 to 62%. In the solid state, the width of the emission band observed at around 650 nm is a clear signature of aggregation. With the trialkoxybenzylimidazolium cations, polarised optical microscopy (POM) and X-ray scattering experiments showed that columnar mesophases were formed. Differential scanning calorimetry (DSC) studies confirmed the mesomorphic behaviour from room temperature to about 130 degrees C for salts with alkyl chains containing 8, 12 and 16 carbon atoms. The strong luminescence of the BODIPY unit was maintained in the mesophase and fluorescence measurements confirmed the presence of J aggregates in all cases. The salt containing the gallate-functionalised imidazolium cations showed no mesomorphism but the acrylate terminal units could be used to engender photoinitiated polymerisation thereby allowing the material to be immobilised on glass plates. The polymerisation process was followed by FTIR spectroscopy and the fixed and patterned films were highly fluorescent with a solid-state emission close to that of the complex in the solid state.

Self-assembly of charged bodipy dyes to form cassettes that display intracomplex electronic energy transfer and accrete into liquid crystals

Red- and blue-absorbing boron dipyrromethene dyes, bearing opposite electronic charges, associate in solution to form a 1:2 complex having a stability constant of ca. 10(17) M(-2). The complex can be dismantled by addition of a large excess of tetra-N-butylammonium cations. The same complex displays liquid crystalline properties on heating from rt to above 150 °C, as characterized by various experimental techniques. Highly efficient electronic energy transfer from the red to the blue dye occurs in both the initial complex and the subsequent mesomorphic state.

Borondipyrromethene Dyes with Pentane-2,4-dione Anchors

New, acetylacetone-linked borondipyrromethene (BODIPY) dyes were readily obtained from BODIPY cores by various protocols involving direct grafting with acetylacetone or cross-coupling from a preorganized phenylacacH derivative bearing either an iodo or an ethynyl function. Facile anchoring on TiO(2) powder is obtained and scrutinized by FT-IR spectroscopy.

Ionic Liquid Crystals Formed by Self-Assembly around an Anionic Anthracene Core

We have designed and synthesised a series of modular, mesogenic complexes based on anthracene-2,6-disulfonate and trialkoxybenzyl-functionalised imidazolium cations. Each complex contains a central, rigid, dianionic anthracene core and two flexible monocations bearing paraffin chains anchored on imidazolium rings. Anthracene-2,6-disulfonate can be crystallised with various simple alkylammonium ions and, in the case of +N(CH3)2(C16H33)2, a crystal structure determination has shown that the long paraffinic chains are intercalated between the anthracene moieties. The dianion forms columnar mesophases with trialkoxybenzylimidazolium cations, as identified by polarising optical microscopy and X-ray scattering measurements. Differential scanning calorimetry studies confirmed mesomorphic behaviour from room temperature to about 200 degrees C for alkyl chains containing 8, 12 and 16 carbon atoms. The strong luminescence of anthracene is maintained in the mesophase and fluorescence measurements confirmed the presence of J aggregates in all cases. The new functional materials described herein provide an easy access to stable and luminescent mesomorphic materials engineered by an ionic self-assembly process.

Near-infrared fluorescent nanoparticles formed by self-assembly of lipidic (Bodipy) dyes.

Fluorescent organic nanoparticles (FONs) formed from p-conjugated frameworks are of immense interest in materials science, most notably as advanced means for imaging of intact biological systems and delivery vehicles. In particular, fluorescent nanoparticles engineered from polymerdoped dyes or small molecules allow fine-tuning of the emissive properties, at least over a restricted wavelength range in the visible window. The highpoint of this research is the intercalation of multiple dyes of disparate optical properties into one-dimensional heterostructures or to promote fluorescence resonance energy transfer within the FONs as a means to induce white-light emission. Small molecular dopants, desirable for cost effectiveness, present special problems in this field since they are prone to segregation into microstructures or aggregates that serve as dark quenchers of local fluorescence. However, in certain cases, emissive aggregates can be assembled from rather small molecules, such as hexaphenylsilole, that themselves are nonemissive when dispersed as monomers. The extension of this work has led to the formulation of systems with which organic dyes are translocated into FONs by lightdriven self-assemblies that provide a means of fluorescence enhancement. Boron-dipyrromethene (Bodipy) dyes, being uncommonly popular fluorescent labels, are susceptible to aggregation in polar solvents and in the solid state. The resultant supramolecular assemblies can be used to tune the color of OLEDs or to examine structure–function relationships for proteins and lipid membranes. In general, the apolar Bodipy dyes form Hor J-aggregates due to facile stacking of the electron-rich dipyrromethene core. In the former structures, the Bodipy planes stack in parallel to give essentially nonfluorescent species featuring a blue-shifted absorption profile. In the J-aggregate, the transition dipoles are not parallel but oriented in planes mutually tilted by an angle governed by the presence of appendages along the Bodipy core. Such aggregates, or dimers, are weakly fluorescent and usually exhibit a modest red-shifted absorption spectrum, which can be well interpreted by conventional excitonic coupling theory. In specific cases, formation of Hand J-aggregates can be controlled by host–guest complexation, macrocyclization, multilayering in polyelectrolytes, and by confinement in sol-gel matrices, or liquid crystalline phases. In seeking to manipulate the type of self-aggregation undertaken by functionalized Bodipy dyes, attention has turned to a central platform decorated with an ammonium cation at the tip and multiple paraffin chains at the outer periphery (Scheme 1). The intention was to achieve a balance between stacking induced by the hydrophobic chains and electrostatic repulsion caused by the localized cationic residues. In particular, it was anticipated that attenuation of the latter charges might be realized by adoption of a tilted geometry that restricted the number of monomers accreted into the final structure. To attain this goal, preliminary materials were designed around trialkoxyphenyl fragments and trimethylammonium head-groups.

Terpyridine-functionalized imidazolium ionic liquids

This paper reports the synthesis and the physical characterization of a new family of chelating ionic liquids carrying a terpyridine fragment suitable for metal extraction.

Excited-state properties of heteroleptic iridium(III) complexes bearing aromatic hydrocarbons with extended cores.

The synthesis, complete structural characterization, electrochemistry, and excited-state dynamics of a series of four bis-heteroleptic iridium(III) charge-transfer complexes composed of a single acac-functionalized and two ortho-metalated 2-phenylpyridine ligands. The formed iodophenyl complex (2) was used as a metallosynthon to introduce extended-core ethynyltolyl (3), ethynylpyrene (4), and ethynylperylene (5) residues into these structures projecting from the acac ancillary ligand. Static and dynamic photoluminescence along with ultrafast and conventional transient absorption measurements in conjunction with cyclic voltammetry were employed to elucidate the nature of the intramolecular energy-transfer processes occurring in the excited states of polychromophores 4 and 5 and are directly compared with those of model complexes 2 and 3. Upon charge-transfer excitation of these molecules, the long-lived triplet-state metal-to-ligand charge-transfer ((3)MLCT)-based photoluminescence readily observed in 2 and 3 (τ = 1 μs) is nearly quantitatively quenched, resulting from production of the associated triplet intraligand ((3)IL) excited states in 4 and 5 through intramolecular triplet-triplet energy transfer. The respective formation of the extended-core (3)*pyrenyl and (3)*perylenyl-localized excited states in 4 and 5 is confirmed by their ultrafast excited-state evolution, which ultimately generates features associated with these (3)IL excited states and their greatly extended excited-state lifetimes with respect to the parent complexes 2 and 3.

Near-Infrared-to-Visible Photon Upconversion Enabled by Conjugated Porphyrinic Sensitizers under Low-Power Noncoherent Illumination

We report four supermolecular chromophores based on (porphinato)zinc(II) (PZn) and (polypyridyl)metal units bridged via ethyne connectivity (Pyr1RuPZn2, Pyr1RuPZnRuPyr1, Pyr1RuPZn2RuPyr1, and OsPZn2Os) that fulfill critical sensitizer requirements for NIR-to-vis triplet-triplet annihilation upconversion (TTA-UC) photochemistry. These NIR sensitizers feature: (i) broad, high oscillator strength NIR absorptivity (700 nm < λ(max(NIR)) < 770 nm; 6 × 10(4) M(-1) cm(-1) < extinction coefficient (λ(max(NIR))) < 1.6 × 10(5) M(-1) cm(-1); 820 cm(-1) < fwhm < 1700 cm(-1)); (ii) substantial intersystem crossing quantum yields; (iii) long, microsecond time scale T1 state lifetimes; and (iv) triplet states that are energetically poised for exergonic energy transfer to the molecular annihilator (rubrene). Using low-power noncoherent illumination at power densities (1-10 mW cm(-2)) similar to that of terrestrial solar photon illumination conditions, we demonstrate that Pyr1RuPZn2, Pyr1RuPZn2RuPyr1, and Pyr1RuPZnRuPyr1 sensitizers can be used in combination with the rubrene acceptor/annihilator to achieve TTA-UC: these studies represent the first examples whereby a low-power noncoherent NIR light source drives NIR-to-visible upconverted fluorescence centered in a spectral window within the bandgap of amorphous silicon.

Lanthanide Ion Extraction by Trifluoromethyl‐1,3‐diketonate‐Functionalised Ionic Liquids Adsorbed on Silica

While acetylacetone (acacH) derivatives are, upon deprotonation, ubiquitous ligands in coordination chemistry, their potential to form stable ionic liquids has not been studied so far. Here we describe a straightforward synthesis of novel trifluoroacetylacetone-functionalised imidazolium salts. These salts are built from an imidazolium ring substituted on one side with a flexible chain of fixed length carrying a terminal acacH group and on the opposite side a paraffin chain of various lengths. By changing the length of these flexible chains (n=4, 8, 12) and the nature of the counter-anions (PF(6)(-), BF(4)(-), NTf(2)(-)), room-temperature ionic liquids were produced. Their application for the extraction of lanthanide salts (Eu, Tb) from dilute aqueous solution has been investigated. The presence of a strong UV absorber (imidazolium ring, λ(abs)=290 nm) allows photosensitisation of the Eu(III) and Tb(III) luminescence by efficient energy transfer, and thus extraction of these two lanthanides can be followed by fluorescence techniques. It appears that loading of the ionic liquids onto silica particles pre-treated with a dilute aqueous solution of NaOH is the most efficient way to obtain fast and almost quantitative (>99.9%) extraction of the metal ions as their diketonato complexes. The procedure is reproducible and the loaded SiO(2) particles can be simply treated with acid to strip the metal ions and regenerate the adsorbed (protonated) extractant.

Microwave-promoted hydrogenation and alkynylation reactions with palladium-loaded multi-walled carbon nanotubes

Multi-walled carbon nanotubes loaded with Pd(0) clusters (average size distribution 9 nm) have been used under microwave irradiation as catalysts in hydrogenation and alkynylation reactions under “eco-friendly” conditions; reduced cinnamic esters and cross-coupled products were obtained in good yields; use of piperidine as the base provided, in a regiospecific process, novel doubly alkynylated compounds unambiguously characterized by NMR correlation experiments and X-ray diffraction.