Teaching Story without Struggle: Using Graded Readers and Their Audio Packs in the EFL Classroom

In recent years the support for extensive reading (ER) in English as a second or foreign language (ESL/EFL) programs has been compelling. When practicing extensive reading, the learner reads a wide variety of texts for pleasure and achieves a general understanding of the content while deciphering unknown words through context. This approach contrasts with intensive reading, a more traditional approach based on a slow, careful reading of a text, with goals of complete comprehension and the identification of specific details and information

Stochastic dynamics of resonance electronic energy transfer in bidimensional overexcited molecular ensembles

We investigate theoretically the stochastic dynamics of Resonance Electronic Energy Transfer (RET), in a bi-dimensional overexcited ensemble of donor and acceptor molecules. We find that, after initial optical excitation of all the donors, the reaction kinetics is well-described by a nonlinear mean-field theory. The latter provides a solid way to define and compute an effective rate of RET, even for disordered samples. We predict that this effective rate scales as R α with R the average distance between individual excited donors and their nearest-neighbor acceptor molecules, and α ∈ [−6, −2] an exponent depending on the spatial distribution of molecular pairs in the sample. Using a kinetic Monte-Carlo approach, we show departures from this macroscopic meanfield description arising from fluctuations and spatial correlations between several molecules involved in the RET process. We expect this prediction to be relevant for both molecular science and biology, where the control and optimization of the RET dynamics is a key issue.Réactions Chimiques, Transfert de Charges et d'Energie en Cavité Electromagnétiqu

Supramolecular tuning of energy transfer efficiency and direction in a bis(styryl) dye–crown ether conjugate

The control of the energy transfer (FRET) in a novel bischromophoric styryl(pyridinium) dye bearing two different crown ether residues is presented. Complexation of the dye with metal cations allows to tune the FRET efficiency without changing the transfer direction or to switch the FRET off, whereas protonation launches the FRET process in the opposite direction relative to the molecular structure. © 2018 Elsevier Lt

Charge-Transfer Chemical Reactions in Nanofluidic Fabry-Pérot Cavities

We investigate the chemical reactivity of molecular populations confined inside a nanofluidic Fabry-Pérot cavity. Due to strong light-matter interactions developing between a resonant electromagnetic cavity-mode and the electric dipole moment of the confined molecules, a polariton is formed. The former gets dressed by environmental vibrational and rotational degrees of freedom of the solvent. We call the resulting polariton dressed by its cloud of environmental excitation a "reacton", since it further undergoes chemical reactions. We characterize how the reacton formation modifies the kinetics of a photoisomerization chemical reaction involving an elementary charge-transfer process. We show that the reaction driving-force and reorganization energy are both modulated optically by the reactant concentration, the vacuum Rabi splitting and the de-tuning between the Fabry-Pérot cavity frequency and targeted electronic transition. Finally, we compute the ultrafast picosecond dynamics of the whole photochemical reaction. We predict that despite optical cavity losses and solvent-mediated non-radiative relaxation, measurable signatures of the reacton formation can be found in state-of-the-art pump-probe experiments.Réactions Chimiques, Transfert de Charges et d'Energie en Cavité ElectromagnétiqueUniversity of Bordeaux Graduate Scholl in Light Sciences & Technologie

Supramolecular tuning of energy transfer efficiency and direction in a bis(styryl) dye–crown ether conjugate

The control of the energy transfer (FRET) in a novel bischromophoric styryl(pyridinium) dye bearing two different crown ether residues is presented. Complexation of the dye with metal cations allows to tune the FRET efficiency without changing the transfer direction or to switch the FRET off, whereas protonation launches the FRET process in the opposite direction relative to the molecular structure. © 2018 Elsevier Lt

Picosecond observation of cation-stepwise delayed and cation-triggered photoinduced intramolecular charge transfer in fluorescent cation probes

Time-resolved transient absorption and gain spectra with subpicosecond laser excitation are reported for donor-donor and acceptor-donor stilbene-crowns (in each compound the electron donor group is the 15-aza-5-crown macrocycle, D1). The effect of the calcium cation on the photoinduced intramolecular charge transfer (ICT) rate constants are measured. When the cation is on the donor side of the molecular system (class 1: D1CS-Crown), the photoinduced ICT process is slowed down and goes through several intermediates characterized by a distancing of the cation, while a solvent molecule enters its coordination sphere. When the cation is on the acceptor side (class 2: D1DS-Crown,D1DB-Crown and D1DCS-Crown), the photoinduced ICT process becomes too fast to be measured, even on the picosecond scale

Transient photoluminescence of para-hexaphenyl layers

International audiencePara-hexaphenyl layers exhibit dramatic changes in their steady-state optical and transient photoluminescence (PL) responses when they are grown with different orientations. For a film in which molecules stand perpendicular to the substrate, radiative recombination of intramolecular Frenkel singlet excitons occurs in less than 2 ps. If the layer is grown with molecules lying parallel to the substrate, short-lived and long-lived PL decay components are found. The former is best reproduced with an annihilation rate equation, characteristic of mobile excitons relaxing in 1 ns while the latter, spectrally redshifted, confirms intermolecular exciton migration

Protonation-Gated Dual Photochromism of a Chromene-Styryl Dye Hybrid

A novel hybrid bisphotochromic system involving a chromene residue and a styryl dye fragment is described. Initially, the compound shows almost no photochromism due to intramolecular energy and electron transfer between the chromophores. Protonation of the hybrid system blocks the transfer processes and unlocks a dual photochromic activity that includes ring opening of the chromene fragment and E-Z-isomerization of the styryl dye residue. Deprotonation of any photoinduced form resets the system to the initial photoinactive form. © 2017 American Chemical Society

Caries imaging by teeth (auto)lumineseence spectral analysis

International audienceWe propose a new technique for caries imaging by the spectral analysis of teeth luminescence excited by the near UV light. This diagnostic/control method can be applied for the all optically accessible teeth surfaces. The photo-physical studies suggest that hydroxylapatite luminescence, excited in the near UV, comes from de-excitation of crystalline structure defects in interaction with charge donating/accepting en ironment