Catherine Hirel

Nitronyl and imino nitroxides: improvement of Ullman's procedure and report on a new efficient synthetic route.

The synthesis of nitronyl and imino nitroxides has been reexamined with the aim of both increasing yields and of offering opportunities for new structures. The conditions for the formation of 2,3-bis(hydroxyamino)-2,3-dimethylbutane, the key intermediate of Ullmans route, have been carefully studied, and a new procedure is proposed, which affords the free base in a very pure form and up to 60% yield. Full characterization of this intermediate including an X-ray crystal structure is presented. An alternative synthetic route through 2,3-diamino-2,3-dimethylbutane and the corresponding imidazolidines which bypasses the delicate synthesis of the bis(hydroxyamino) compound is described. It is shown that 3-chloroperbenzoic acid is an effective oxidant for the transformation of adequately substituted imidazolidines into nitronyl nitroxides, which are obtained in high yield. An illustration of the potentialities of this new route, a new nitronyl nitroxide with two ethyl substituents in positions 4 and 5 of the imidazoline ring, is reported. The scope and limitations of the two routes are discussed.

ABAB homoleptic bis(phthalocyaninato)lutetium(III) complex: toward the real octupolar cube and giant quadratic hyperpolarizability.

The concept of octupolar molecules has considerably enlarged the engineering of second-order nonlinear optical materials by giving access to 2D and 3D architectures. However, if the archetype of octupolar symmetry is a cube with alternating donor and acceptor groups at the corners, no translation of this ideal structure into a real molecule has been realized to date. This may be achieved by designing a bis(phthalocyaninato)lutetium(III) double-decker complex with a crosswise ABAB phthalocyanine bearing alternating electron-donor and electron-acceptor groups. In this communication, we present the first step toward this goal with the synthesis, crystal structure determination, and measurement of the molecular first-order hyperpolarizability β by harmonic light diffusion, of an original lutetium(III) sandwich complex displaying the required ABAB-type alternation for one face of the cube. This structure is characterized by an intense absorption in the near-IR due to an intervalence transition and exhibits the highest quadratic hyperpolarizability ever reported for an octupolar molecule, √ = 5750 × 10(-30) esu.

The cyano nitronyl nitroxide radical: experimental and theoretical evidence for the fourth case of the McConnell-I mechanism.

The nitronyl nitroxide 2-cyano-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (1) crystallises in the tetragonal P42(1)m space group with a=7.4050(7), c=8.649(1) A. In the crystal the molecules form layers parallel to the ab plane in which they are orthogonal to each other. In the layers there are close contacts, 2.953(2) A, between the NO groups and the bridging carbon atoms of the O-N-C-N-O fragment of neighbouring radicals. The calculated spin density shows a positive population mainly and equally localised on the NO groups and small but significant negative spin densities on the bridging carbon atom and the cyano nitrogen. Absorption spectra show temperature-dependent transitions related to the magnetic behaviour. The temperature dependence of the magnetic susceptibility in the range 2-300 K reveals that couplings between the radicals are antiferromagnetic, and is interpreted by considering a two-dimensional square array of spin S=1/2 antiferromagnetically coupled (J=-10 cm(-1) and g=2.01). This is interpreted as an exchange coupling through close contact between positive and negative spin densities in orthogonal orbitals on oxygen and carbon atoms, respectively.

Fluorescence and FTIR Spectra Analysis of Trans-A2B2- Substituted Di- and Tetra-Phenyl Porphyrins

A series of asymmetrically substituted free-base di- and tetra-phenylporphyrins and the associated Zn-phenylporphyrins were synthesized and studied by X-ray diffraction, NMR, infrared, electronic absorption spectra, as well as fluorescence emission spectroscopy, along with theoretical simulations of the electronic and vibration structures. The synthesis selectively afforded trans-A2B2 porphyrins, without scrambling observed, where the AA and BB were taken as donor- and acceptor-substituted phenyl groups. The combined results point to similar properties to symmetrically substituted porphyrins reported in the literature. The differences in FTIR and fluorescence were analyzed by means of detailed density functional theory (DFT) calculations. The X-ray diffraction analysis for single crystals of zinc-containing porphyrins revealed small deviations from planarity for the porphyrin core in perfect agreement with the DFT optimized structures. All calculated vibrational modes (2162 modes for all six compounds studied) were found and fully characterized and assigned to the observed FTIR spectra. The most intense IR bands are discussed in connection with the generic similarity and differences of calculated normal modes. Absorption spectra of all compounds in the UV and visible regions show the typical ethio type feature of meso-tetraarylporphyrins with a very intense Soret band and weak Q bands of decreasing intensity. In diphenyl derivatives, the presence of only two phenyl rings causes a pronounced hypsochromic shift of all bands in the absorption spectra. Time-dependent DFT calculations revealed some peculiarities in the electronic excited states structure and connected them with vibronic bands in the absorption and fluorescence spectra from associated vibrational sublevels.

ABAB homoleptic bis(phthalocyaninato)lanthanide(III) complexes: original octupolar design leading to giant quadratic hyperpolarizability.

The octupolar cube, a Td symmetry cube presenting alternating charges at its corners, is the generic point charge template of any octupolar molecule. So far, transposition into real molecular structures has yet to be achieved. We report here a first step toward the elaboration of fully cubic octupolar architectures. A series of octupolar bis(2,3,16,17-tetra(hexylthio)phthalocyaninato)lanthanide double-decker complexes [Pc2Ln], Ln = Nd (1), Eu (2), Dy (3), Y (4), and Lu (5), are described, whose original three-dimensional structures display the required alternation of ABAB type for one face of the cube and the delocalization between the two rings approximating to the electronic interaction along the edges of the cube. Synthesis, X-ray crystal structure, and study of the optical properties and of the first molecular hyperpolarizability β are reported. The size of the lanthanide (III) central ion modulates the ring-to-ring distance and the degree of coupling between the two phthalocyanine rings. As a consequence, the optical properties of these octupolar chromophores and in particular the strong near-infrared absorption due to the intervalence transition between the two rings also depend on the central lanthanide (III) ion. The first oxidized and reduced states of the complexes, while keeping a similar octupolar structure, display considerably changed optical properties compared to the neutral states. Second-order nonlinear properties were determined by nonpolarized harmonic light scattering in solution at 1907 nm. Exceptionally large dynamic molecular first hyperpolarizabilities √(1907), among the highest ever reported, were found that showed a strong dependence on the number of 4f electrons.

Design of oxygen sensing nanomaterial: synthesis, encapsulation of phenylacetylide substituted Pd(II) and Pt(II) meso-tetraphenylporphyrins into poly(1-trimethylsilyl-1-propyne) nanofibers and influence of silver nanoparticles

Room temperature phosphorescent oxygen sensors have been designed by embedding symmetric palladium(II) or platinum(II) meso-tetraphenylporphyrins in poly(1-trimethylsilyl-1-propyne) in the form of nanofibers along with/without silver nanoparticles. These materials combine the advantages of the high oxygen sensitivity of porphyrins and the enhanced surface area of porous nanofibers. Phenylacetylide bearing palladium(II) or platinum(II) meso-tetraphenylporphyrins (Pd-TPA, Pt-TPA, Pd-TPP and Pt-TPP) were designed to enhance phosphorescence quantum yields as well as sensitivity towards oxygen. Their syntheses were achieved by 2 alternative methods including successive metallation reactions and Sonogashira coupling via optimization of the synthetic strategies and conditions. The respective effect of the metal (Pd or Pt) and substituent on phosphorescence quantum yield as well as other photophysical properties was considered. The sensing performances of the corresponding silver-free and silver doped nanofibers were tested in the oxygen concentration range of 0.0–100.0%. The offered composites provided the advantages of fast response, enhanced sensitivity, reversible and long lasting response, higher Stern–Volmer constants (KSV) and low limit of detection values extending to 7.5 ppm for oxygen.

Phthalonitriles Functionalized for Click Chemistry. Design, Synthesis and Structural Characterization

AbstractTwo phthalonitriles complementarily functionalized by an azide and an alkyne function have been designed for the click Huisgen azide-alkyne dipolar addition reaction. Their synthesis and full structural characterization is presented here with a comparative approach.Graphical AbstractTwo phthalonitriles complementarily functionalized by an azide and an alkyne function and their full structural characterization is presented with a comparative approach..

Significant sensitivity and stability enhancement of tetraphenylporphyrin-based optical oxygen sensing material in presence of perfluorochemicals

Emission-based oxygen sensing properties of highly luminescent tetraphenylporphyrin molecules were investigated in polystyrene, ethyl cellulose, poly(1-trimethylsilyl-1-propyne) and poly(isobutylmethacrylate) matrices. The effect of perfluorochemicals (PFCs) on oxygen sensitivity and stability of the sensor materials was also examined. Fluorescence intensity and lifetime measurements of meso-tetraphenylporphyrinato Zn(II) (ZnTPP) and meso-tetraphenylporphyrin (H2TPP) materials were performed in the concentration range of 0–100% pO2. The fluorescence intensity variation of H2TPPvs. oxygen was 86%. H2TPP-based composite also yielded higher Stern–Volmer constant, faster response and regeneration time, excellent long term photostability and larger linear response range with respect to ZnTPP. The detection limit of oxygen for H2TPP was less than 0.5%. When stored in sealed bags protected from sunlight, no decrease in oxygen sensitivity was observed during approximately five months. As far as we know, the gathe...

Lifetime-Based Oxygen Sensing Properties of palladium(II) and platinum(II) meso-tetrakis(4-phenylethynyl)phenylporphyrin

High oxygen permeable [poly(TMSP)] nanofibers incorporating porphyrin macrocycle as luminescence indicators were prepared by electrospinning technique. The porphyrins involves were modified by i) introducing phenylacetylide substituents on the para position of the phenyl moieties and ii) varying the metal centers [Pt(II) or Pd(II)] of the meso-tetrakisphenylporphyrins. A set of nanofibers; (Pt-TPP)NF, (Pd-TPP)NF, (Pt-TPA)NF and (Pd-TPA)NF were obtained to study their structure-activity relationship toward oxygen. The lifetime-based technique was privileged to take advantage of their long-lived phosphorescent properties. A two-fold enhancement was observed for (Pt-TPA)NF and (Pd-TPA)NF compared to (Pt-TPP)NF and (Pd-TPP)NF demonstrating the positive effect of the phenylacetylide moieties on the lifetime. Also, Silver nanoparticles were included in nanofibers to investigate their influence on lifetime-based oxygen sensitivity, showing that the presence of AgNPs only affects (Pd-TPA)NF.

Mechanism of the Zn(II)Phthalocyanines’ Photochemical Reactions Depending on the Number of Substituents and Geometry

In this work, the synthesis and the nonlinear absorption and population dynamics investigation of a series of zinc phthalocyanines (ZnPcs) dissolved in chloroform are reported. In order to determine the relevant spectroscopic parameters, such as absorption cross-sections of singlet and triplet excited states, fluorescence relaxation times, intersystem crossing, radiative decay and internal conversion, different optical and spectroscopic techniques were used. By single pulse and pulse train Z-scan techniques, respectively, singlet and triplet excited states‘ absorption cross-section were determined at 532 nm. Furthermore, the intersystem crossing time was obtained by using both techniques combined with the fluorescence lifetime determined by time-resolved fluorescence. The radiative and internal conversion rates were determined from the fluorescence quantum yield of the samples. Such spectroscopy parameters are fundamental for selecting photosensitizers used in photodynamic therapy, as well as for many other applications.