Chantal Andraud

Long-Lived Two-Photon Excited Luminescence of Water-Soluble Europium Complex: Applications in Biological Imaging Using Two-Photon Scanning Microscopy

A new europium complex presenting good solubility and stability in water, intense emission in the red (616 nm), long luminescence lifetime, and significant two-photon absorption cross-section in the biological window has been designed and successfully used for two-photon scanning microscopy bioimaging experiments on fixed cancer cells.

Efficient Sensitization of Europium, Ytterbium, and Neodymium Functionalized Tris-Dipicolinate Lanthanide Complexes through Tunable Charge-Transfer Excited States

A series of push-pull donor-pi-conjugated dipicolinic acid ligands and related tris-dipicolinate europium and lutetium complexes have been prepared. The ligands present broad absorption and emission transitions in the visible spectral range unambiguously assigned to charge-transfer transitions (CT) by means of time-dependent density functional theory calculations. The photophysical properties (absorption, emission, luminescence quantum yield, and lifetime) of the corresponding europium complexes were thoroughly investigated. Solvatochromism and temperature effects clearly confirm that Eu(III) sensitization directly occurs from the ligand CT state. In addition, modulation of the energy of the CT donating state by changing the nature of the donor fragment allows the optimal energy of the antennae for europium sensitization to be determined, and this optimal energy was found to be close to the (5)D 1 accepting state. Finally, this CT sensitization process has been successfully extended to near-infrared emitters (neodymium and ytterbium).

Two-photon absorption and optical power limiting of bifluorene molecule

We have studied the nonlinear absorption spectra and optical limiting properties of 2,2′-(9,9-dihexyl) bifluorene. Measurements were done in chloroform solution, in the visible range (450–650 nm), and for nanosecond time-duration pulses. The two-photon absorption (TPA) spectrum, obtained by the up-conversion fluorescence method, shows a resonance at λ=534 nm with a cross-section σTPA=60 10−50 cm4⋅s/photon-molecule. Semiempirical quantum chemistry calculation on fluorene and bifluorene suggests an enhancement of the bifluorene TPA due to coupling effects between monomers. In nonlinear transmission measurements, two-photon absorption is reinforced by the excited-state absorption that occurs during the pulse duration. At resonance, the three-photon absorption coefficient is α3=14 000 cm3/GW2 for a bifluorene concentration of 600 g/L. This strong nonlinear absorption leads to an efficient optical power limiting in the green and blue parts of the spectrum. The maximum transmitted energy is lower than 10 μJ for an input energy of up to 200 μJ in a F/5 optical geometry.

Very bright europium complexes that stain cellular mitochondria

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.

Three-dimensional microfabrication by two-photon-initiated polymerization with a low-cost microlaser

Fabrication of submicrometer structures by two-photon-initiated polymerization is performed with an inexpensive and low-power microlaser. This is made possible by the design of photoinitiators with strong two-photon absorption cross sections. We analyze the influence of both material properties and irradiation conditions on the two-photon polymerization rate and show that resins based on our highly sensitive two-photon photoinitiator can be solidified with microlaser excitation, whereas commercial UV photoresins require ultrashort and intense laser pulses.

Design of Dipicolinic Acid Ligands for the Two-Photon Sensitized Luminescence of Europium Complexes with Optimized Cross-Sections

The multistep synthesis of an extensive series of push-pull donor-pi-conjugated dipicolinic acid ligands is described. The charge transfer character of the ligand can be tuned by changing the donor group (CH 2R, OR, SR, or NR 2) or the nature of the conjugated backbone (phenyl, phenylethynyl, naphtylethynyl, bis(phenylethynyl), or chalcone). The photophysical properties of related D 3 symmetric europium complexes (absorption and luminescence) were measured. Experiments using two-photon sensitized luminescence of a Eu (III) complex reveal large two-photon absorption (TPA) cross-section values (775 GM at 740 nm) in dichloromethane. Furthermore, some structure-property relationships can be derived from this systematic study, allowing an optimization of TPA properties of lanthanide complexes.

Ytterbium-Based Bioprobes for Near-Infrared Two-Photon Scanning Laser Microscopy Imaging†

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Ytterbium-based bioprobes for near-infrared two-photon scanning laser microscopy imaging. Anthony D’Aléo, Adrien Bourdolle, Sophie Brustlein, Teddy Fauquier, Alexei Grichine, Alain Duperray, P. L. Baldeck, Chantal Andraud, Sophie Brasselet, Olivier Maury

Continuous Symmetry Breaking Induced by Ion Pairing Effect in Heptamethine Cyanine Dyes: Beyond the Cyanine Limit

The association of heptamethine cyanine cation 1(+) with various counterions A (A = Br(-), I(-), PF(6)(-), SbF(6)(-), B(C(6)F(5))(4)(-), TRISPHAT) was realized. The six different ion pairs have been characterized by X-ray diffraction, and their absorption properties were studied in polar (DCM) and apolar (toluene) solvents. A small, hard anion (Br(-)) is able to strongly polarize the polymethine chain, resulting in the stabilization of an asymmetric dipolar-like structure in the crystal and in nondissociating solvents. On the contrary, in more polar solvents or when it is associated with a bulky soft anion (TRISPHAT or B(C(6)F(5))(4)(-)), the same cyanine dye adopts preferentially the ideal polymethine state. The solid-state and solution absorption properties of heptamethine dyes are therefore strongly correlated to the nature of the counterion.

On the Computation of Adiabatic Energies in Aza-Boron-Dipyrromethene Dyes

We have simulated the optical properties of Aza-Boron-dipyrromethene (Aza-BODIPY) dyes and, more precisely, the 0-0 energies as well as the shape of both absorption and fluorescence bands, thanks to the computation of vibronic couplings. To this end, time-dependent density functional theory (TD-DFT) calculations have been carried out with a systematic account of both vibrational and solvent effects. In a first step, we assessed different atomic basis sets, a panel of global and range-separated hybrid functionals as well as different solvent models (linear-response, corrected linear-response, and state-specific). In this way, we have defined an accurate yet efficient protocol for these dyes. In a second stage, several simulations have been carried out to investigate acidochromic and complexation effects, as well as the impact of side groups on the topology of the optical bands. In each case, theory is able to accurately reproduce experimental results and the proposed protocol is consequently useful to design new dyes featuring improved properties.

Near-Infrared Nitrofluorene Substitued Aza-Boron-dipyrromethenes Dyes

The synthesis, spectroscopic properties, and TD-DFT calculations of new aza-Boron-dipyromethene dyes featuring pendant nitrofluorenylethynyl substituents are described. This functionalization allows for moving the luminescence in the NIR, conserving a good quantum yield efficiency.