The photophysical and nonlinear optical properties of water-soluble chromophore-functionalised tris-dipicolinate complexes [LnL3](3-) (Ln=Yb and Nd) are thoroughly studied, revealing that only the Yb(III) luminescence can be sensitized by a two-photon excitation process. The stability of the complex in water is strongly enhanced by embedding in dispersible organosilicate nanoparticles (NPs). Finally, the spectroscopic properties of [NBu4]3 [YbL3] are studied in solution and in the solid state. The high brightness of the NPs allows imaging them as single objects using a modified two-photon microscopy setup in a NIR-to-NIR configuration.

Bright nano objects emitting in the near infrared with a maximal cross section of 41.4 x 103 GM (Goppert Mayer), were prepared by implanting ca. 180 4,4’–diethylaminostyryl–2,2’–bipyridine (DEAS) Yb(III) complexes on the surface of 12–nm silica nanoparticles. The surface complexes Ln@SiO 2 ], Ln =Y,Yb) were characterized using IR, solid–state NMR, UV–Vis, EXAFS spectroscopies in combination with the preparation and characterization of similar molecular analogues by analytical techniques (IR, solution NMR, UV–Vis, X ray crystallography) as well as DFT calculations. Starting from the partial dehydroxylation of the silica at 700 °C on high vacuum having 0.8 OH.nm–2, the grafting of Ln(N(SiMe 3 ) 2 ) 3 generate ≡SiO–Ln(N(SiMe 3 ) 2 ) 2 , which upon thermal step and coordination of the DEAS chromophore yields (≡SiO) 3 Ln(DEAS). Surface and molecular analogues display similar properties, in terms of DEAS binding constants absorption maxima and luminescence properties (intense emission band assigned to a ligand centered CT fluorescence and life time) in the solid state, consistent with the molecular nature of the surface species. The densely functionalized nanoparticles can be dispersed via ultra-sonication in small ca. 15-20 nm aggregates (1 to 6 elementary particles) that were detected using two–photon microscopy imaging at 720 nm excitation, making them promising nano– objects for bio–imaging.

Bright nano-objects emitting in the near-infrared with a maximal cross section of 41.4 × 103 GM (Goppert Mayer) were prepared by implanting ca. 180 4,4′-diethylaminostyryl-2,2′-bipyridine (DEAS) Yb(III) complexes on the surface of 12-nm silica nanoparticles. The surface complexes ([DEAS·Ln@SiO2], Ln = Y, Yb) were characterized using IR, solid-state NMR, UV-vis, and EXAFS spectroscopies in combination with the preparation and characterization of similar molecular analogues by analytical techniques (IR, solution NMR, UV–vis, X-ray crystallography) as well as DFT calculations. Starting from the partial dehydroxylation of the silica at 700 °C under a high vacuum having 0.8 OH·nm–2, the grafting of Ln(N(SiMe3)2)3 generates ≡SiO–Ln(N(SiMe3)2)2, which upon thermal step and coordination of the DEAS chromophore yields (≡SiO)3Ln(DEAS). Surface and molecular analogues display similar properties, in terms of DEAS binding constants absorption maxima and luminescence properties (intense emission band assigned to a liga...

The synthesis of tris(2-thenoyltrifluoroacetonate)lanthanide(III) complexes featuring a diethylaminostyryl-2,2'-bipyridine coligand was achieved for lanthanum; the near-infrared (NIR) emitters neodymium, erbium, and ytterbium; and the transition-metal yttrium. The photophysical properties were thoroughly studied, and it was demonstrated that the conjugated bipyridine ligand acts as a good antenna for the sensitization of the NIR emitters. The two-photon absorption (TPA) properties of all five complexes were investigated by using both two-photon excited fluorescence and the Z-scan method. We demonstrate that the nature of the rare earth ion has almost no influence on the TPA properties centered on the conjugated bipyridyl ligand. Finally, we show that Yb(III) is sensitized by a two-photon antenna effect, and that Nd(III) is mostly sensitized by a one-photon process involving direct excitation of forbidden f-f transitions.

Using a spray-drying process, we developed a versatile, one step synthesis, of two-photon luminescent silicate nanoparticles. The formation of the nanoparticles is based on the controlled drying of sol-gel droplets in a heated laminar flux inside a tubular furnace. Two types of nanoparticles were prepared, hybrid core-shell nanoparticles and silicate nanoparticles doped with an europium(III) complex. In the first case of hybrid (organic-silicate) coreshell nanoparticles the fast evaporation of THF solvent enhance the polycondensation of the silicate network in the droplets, particularly at their surface. This induces first the formation of a silicate crust followed, at the end of the solvent evaporation, by the nucleation and growth of the organic dye in the core of the resulting dried nanoparticles. We studied the different physical and chemical parameters that influence the perfect and reproducible control of the confined nucleation and growth of dye nanocrystals in the sol-gel droplets. In the second case, silicate nanoparticles were doped with a functionalized tris-dipicolinate europium complex, which presents an important two-photon absorption cross section but exhibits a weak stability in water due to the dissociation of the complex. Two different compositions of the starting sols were tested to adjust the hydrophilic character of the nanoparticles and to avoid the dissociation of the europium complexes in water by closing the porosity of the silicate shell.

The synthesis, structure and photophysical properties of a series of highly emissive europium complexes is reported. Certain complexes enter mammalian cells by macropinocytosis and stain the mitochondria selectively, allowing observation of the Eu emission in cellulo by time-gated spectral imaging.

A series of non-aqueous solvents combined with the exogenous biradical bTbK are developed for DNP NMR that yield enhancements comparable to the best available water based systems. 1,1,2,2-tetrachloroethane appears to be one of the most promising organic solvents for DNP solid-state NMR. Here this results in a reduction in experimental times by a factor of 1000. These new solvents are demonstrated with the first DNP surface enhanced NMR characterization of an organometallic complex supported on a hydrophobic surface.

Nimm zwei: Die Entwicklung und Charakterisierung eines stabilen makrocyclischen Ytterbium-Komplexes, der einen durch Zwei-Photonen-Absorption anregbaren Antennen-Liganden trägt, wird beschrieben (siehe Bild). Die biphotonische Sensibilisierung der Nahinfrarot-Lumineszenz von Ytterbium(III) und die Konzeption eines biphotonischen Nahinfrarot-Mikroskops ermöglichen die detailgetreue Abbildung dicker Gewebeproben.

Functionalized tris-dipicolinate europium(III) complexes present a very important two-photon absorption cross-section (up to 775 GM) but exhibit a weak stability in aqueous solutions due to the ligand substitution by water molecules. This dissociation decreases radically the luminescence quantum yield and lifetime of the complex. In this paper, we present a one-step alternative route to stabilize these lanthanide complexes in aqueous solutions or in aqueous buffer solutions by embedding them in silica nanoparticles (NPs). This simple one-step method is based on the spray-drying of sol-gel solutions involving silicon alkoxides as precursors of the silica NPs, hydrolyzed through a small amount of water, an organic solvent and the dissolved Eu(III) complex. These atomized sols are dried under laminar air flow in a tubular furnace while the resulting NPs were collected with an electrostatic filter. Different types of silicon alkoxides were used to adjust the hydrophilic character and porosity of NPs, to optimize their biocompatibility and dispersion in aqueous solutions and to avoid the Eu(III) complexes dissociation. The chemical stability in aqueous solutions of the Eu-complexes inserted in the different NPs was followed through their luminescence spectroscopy and two-photon microscopy to determine the optimal chemical composition of the starting sols for the preparation of highly luminescent water stable bio-labels.

Silica nanoparticles with a surface functionalized by two-photon absorbing (≡SiO)Zn(OSi(OtBu)3)(DEAS-bipy) chromophores are prepared via surface chemistry controlled at the molecular level. This involves the grafting of {Zn[OSi(OtBu)3]2}2 on the surface silanols of a silica partially dehydroxylated at 700 °C followed by the coordination of DEAS-bipy. The spectroscopic and photophysical properties of the grafted species (≡SiO)Zn(OSi(OtBu)3)(DEAS-bipy) compare well with that of the molecular model {DEAS-bipyZn(OAc)2} with the advantage of allowing a high density of chromophores on a nanometric object (ca. 200 chromophores per silica particle of 12 nm). These particles are luminescent and exhibit a giant two-photon cross-section of about 90 × 103 GM; such two-photon brightness allows the imaging of a single nanoparticle using two-photon scanning microscopy.

In the [Er(hfac)(3)(L)](2) complex (1) (L = 4-tetrathiafulvalene-2,6-pyridinecarboxylic acid dimethyl ester), the Er(III) ion is bonded to the tridentate coordination site. Electrochemical and photophysical measurements in solution reveal that the tetrathiafulvalene moiety is a versatile antenna for erbium luminescence sensitization at 6540 cm(-1) upon excitation in the low-energy charge transfer transition (donor to acceptor charge transfer) at 16600 cm(-1) assigned via time-dependent density functional theory calculations.

We describe how the association between an ytterbium ion and a ruthenium carbon-rich complex enables the first switching of the near-IR Yb(III) luminescence by taking advantage of the redox commutation of the carbon-rich antenna.

Two europium complexes with bis(bipyridine) azamacrocyclic ligands featuring pendant arms with or without π-conjugated donor groups are synthesized and fully characterized by theoretical calculations and NMR spectroscopy. Their photophysical properties, including two-photon absorption, are investigated in water and in various organic solvents. The nonfunctionalized ligand gives highly water-stable europium complexes featuring bright luminescence properties but poor two-photon absorption cross sections. On the other hand, the europium complex with an extended conjugated antenna ligand presents a two-photon absorption cross section of 45 GM at 720 nm but is poorly luminescent in water. A detailed solvent-dependent photophysical study indicates that this luminescence quenching is not due to the direct coordination of O-H vibrators to the metal center but to the increase of nonradiative processes in a protic solvent induced by an internal isomerization equilibrium.