Arnaud Brosseau

White Fluorescence from Core–Shell Silica Nanoparticles†

Into the white: Encapsulation of a naphthalimide moiety in the core of silica nanoparticles afforded nanospheres with a strong green excimeric emission. Together with the blue emission of the monomeric naphthalimide and the yellow fluorescence of the tetrazine acceptor on the outer shell, the added contributions provide intense white fluorescence upon 330 nm UV excitation.

A new immunosensor for breast cancer cell detection using antibody-coated long alkylsilane self-assembled monolayers in a parallel plate flow chamber

We designed a new efficient and reliable immunosensor and demonstrated its analytic performance to capture breast cancer MCF7 and T47D cells, under laminar flow, onto antibody-coated long alkylsilane self-assembled monolayers (SAMs) in a parallel plate flow chamber. The surface floor of the laminar flow chamber was grafted with an amino-terminated long alkyl chain spacer, 21-aminohenicosyl trichlorosilane (AHTS) followed by tethering a specific monoclonal antibody directed against the human epithelial cell adhesion molecule (EpCAM) antigen, which is overexpressed in primary breast cancer. Properties of the AHTS- and antibody-grafted surface floor were compared to that of surface floors coated with the short alkyl spacers 3-glycidoxy-propyl trimethoxysilane (GPTS) or 3-aminopropyl triethoxysilane (APTES) and antibodies. A theoretical model was constructed according to the geometry of the flow chamber in order to calculate the trajectories that would use cell flows. Cell capture experiments demonstrated that cell immobilization was optimized throughout the whole flow chamber. High cell capture was yielded on antibody-tethered long alkyl AHTS surface. This new procedure offers multiple advantages: a versatile tool readily applied to a panel of purified antibodies, an enrichment of cell immobilization using repetitive cell flow, and a stable capturing surface suitable for long term storage and handling.

Synthesis and characterization of core-shell structure silica-coated Fe29.5Ni70.5 nanoparticles

In view of potential applications of magnetic particles in biomedicine and electromagnetic devices, we made use of the classical Stober method-base-catalyzed hydrolysis and condensation of tetraethoxysilane (TEOS)-to encapsulate FeNi nanoparticles within a silica shell. An original stirring system under high power ultrasound made it possible to disperse the otherwise agglomerated particles. Sonication guaranteed particles remained dispersed during the Stober synthesis and also improved the efficiency of the method. The coated particles are characterized by electron microscopy (TEM) and spectroscopy (EDX) showing a core-shell structure with a uniform layer of silica. Silica coating does not affect the core magnetic properties. Indeed, all samples are ferromagnetic at 77 K and room temperature and the Curie point remains unchanged. Only the coercive force shows an unexpected non-monotonic dependence on silica layer thickness.

Photoswitchable interactions between photochromic organic diarylethene and surface plasmon resonance of gold nanoparticles in hybrid thin films

Hybrid materials combining gold nanoparticles (GNP) of variable diameter and an organic thin layer of photochromic diarylethenes were achieved. Solid-state photoswitching based on ring-closure/ring-opening reaction was carried out under alternate UV and visible irradiations. In addition to the spectral changes due to the photochromism itself, the surface plasmon resonance related to the GNP is significantly modified, influenced by a photoinduced change in the refractive index of its environment. These two contributions were sorted out, showing the possibility of probing a photochromic switch by following the plasmon band. The shape change of the plasmon band was consistently compared to calculations based on the Mie theory. Additionally, with one given diarylethene compound, both UV-visible spectroscopy and surface enhanced Raman scattering (SERS) spectroscopy showed an acceleration of the ring-opening photochromic reaction in the presence of GNP.

Visible-emitting hybrid sol–gel materials comprising lanthanide ions: thin film behaviour and potential use as phosphors for solid-state lighting

The synthesis and characterization, as well as the film-forming and luminescent properties of four visible-emitting hybrid organic–inorganic sol–gel materials are reported. They show thermal stability up to 165 °C. Deposition conditions were optimized to coat these materials as homogeneous and transparent thin films (∼50 nm) of a smooth surface, as probed by AFM. They were specifically designed to emit the three primary colours. The blue-emitting material 1 was made up of a polyfluorene derivative embedded into a silica matrix, while the green (2) and red (3)-emissive materials comprise the TbIII and EuIII ions bound to the matrix, respectively. The films showed relatively high emission quantum yield efficiencies, with values of 19% (blue), 46% (green), and 21% (red). The three emitters were used to design a single emissive material (4) that showed emission from yellow-green to blue in a wide range of excitation wavelengths (254–380 nm). In particular, white light was obtained for excitation at 340 nm. The EuIII material was investigated as a potential phosphor coated on an UV LED, and primary investigations on its stability under operating conditions are reported.

Photoactive chelating organic nanospheres as central platforms of bimodal hybrid nanoparticles

An innovative approach based on the combination of pre-formed nano-objects using photoactive chelating organic nano-platforms has been developed to elaborate hybrid functional nanoparticles. In this way, original “raspberry-like” structures made of a self-assembled fluorescent organic core surrounded by magnetic nanoparticles have been obtained. The resulting fluo@mag architecture exhibits strong brilliance and magnetization compared to the usual structures made of an inorganic core. The reported fabrication procedure represents a simple and very general method which can be applied to any couple of units displaying complementary complexing abilities to yield dense magneto- and photoactive nanomaterials whose core emission appears advantageously insensitive to the surroundings.

Probing photochromic properties by correlation of UV-visible and infra-red absorption spectroscopy: a case study with cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene

Quantification of the relative composition of the isomers in a photochromic system at any irradiation time interval is a critical issue in determining absolute quantum yields. For this purpose, we have developed a simple and convenient protocol involving combination of UV-visible and infra-red absorption spectroscopy. Photochromic cyclization reaction of cis-l,2-dicyano-l,2-bis(2,4,5-trimethyl-3-thieny1)ethene (CMTE) is analyzed to demonstrate the efficiency of the proposed methodology. This approach is based on the fact that the two isomers show distinctive infra-red bands. Detailed investigations of the UV-visible and infra-red spectra of the mixture obtained at different irradiation times in CCl(4) supported by quantum chemical computations lead to the unambiguous estimation of molar absorption coefficients of the closed isomer (epsilon(CF) = 4650 L mol(-1) cm(-1) at 512 nm). It facilitates the first determination of absolute quantum yields of this reversible photochromic reaction in CCl(4) by fitting the UV-visible spectral data (Phi(OF-->CF) = 0.41 +/- 0.05 and Phi(CF-->OF) = 0.12 +/- 0.02 at 405 nm and 546 nm, respectively).

Aerobic Palladium(II)-Catalyzed Dehydrogenative Heck Reaction in the Synthesis of Pyrenyl Fluorophores. A Photophysical Study of β-Pyrenyl Acrylates in Solution and in the Solid State

An aerobic dehydrogenative Heck reaction of pyrene (1a) and 2,7-di-tert-butylpyrene (1b) with ethyl acrylate is reported. The reaction is catalyzed by a Pd(OAc)2/4,5-diazafluoren-9-one (DAF) system and takes place in acetic or pivalic acid as solvents at 110-130 °C. The reaction of 1a afforded a 6:1 mixture of C-1- and C-4-alkenylated pyrenes (2a and 3a, respectively) in 71% yield. In the case of 1b, only a C-4-substituted product (3b) was formed in 46% yield. Compounds 2a and 3a,b exhibited fluorescence in solution and in the solid state. In chloroform and THF solution the fluorescence maxima were in the range of 440-465 nm, and quantum yields decreased in the order 2a > 3a> 3b. In the solid state, 3a,b showed blue-green fluorescence (ΦF = 0.26 and 0.14, respectively), whereas 2a emitted yellow-green fluorescence) (ΦF = 0.35). Besides blue-emitting monomers, the presence of green-emitting aggregated species (preformed dimers) in the crystals of 3a,b and red-emitting dynamic excimers in the crystals of 2a has been demonstrated. Single-crystal X-ray diffraction analyses of 2a and 3b confirmed π-stacking of pyrenyl moieties in the crystals of the former and the absence of stacking in the crystals of the latter compound.

Fluorescent and Electroactive Low-Viscosity Tetrazine-Based Organic Liquids

New fluorescent molecular liquids with a tetrazine core have been prepared. These compounds remain liquid at least down to -60 °C and display very low viscosities (28 mPa.s for liquid 1, 58 mPa.s for liquid 2). Both compounds remain fluorescent in the condensed phase. For liquid 1, intermolecular quenching is observed to a certain extent, whereas liquid 2 displays similar photophysical properties in dilute solution and in neat film.

Efficient synthesis of pyrene-1-carbothioamides and carboxamides. Tunable solid-state fluorescence of pyrene-1-carboxamides

Pyrene reacts with potassium thiocyanate and organic isothiocyanates in the presence of trifluoromethanesulfonic acid to afford primary and secondary pyrene-1-carbothioamides in high yields. These compounds were efficiently oxidatively desulfurized with Oxone® to the corresponding carboxamides. The amides display solid-state fluorescence with quantum efficiencies up to 62%, originating from monomers, aggregates (such as preformed dimers), and/or excimers, depending on the substituent at the nitrogen atom. Single crystal X-ray diffraction characterization of one highly emissive compound supports this assumption.