Tunable double photochromism of a family of bis-DTE bipyridine ligands and their dipolar Zn complexes.

International audienceThe photoinduced ring-closure/ring-opening reactions of a series of bis-dithienylethene derivatives, as free ligands and Zn(II)-complexes, are investigated by resorting to theoretical (time-dependent density functional theory) and kinetic analyses in solution. The originality of the system stems from the tunability of the photoreaction quantum yields and conversion yields as a function of the electronic structure. The latter could be varied by modifying the electron-donating character of the DTE-end substituents L(a-d) (o,o) (a, D = H; b, D = OMe; c, D = NMe(2); d, D = NBu(2)) and/or the Lewis character of the metal ion center L(a-d)ZnX(2) (o,o) (L(a-c), X = OAc; L(d), X = Cl). The orbital description of the doubly-open form (o,o) and half-closed form (o,c) predicts that double closure to the form (c,c) would occur using UV irradiation. Photokinetic studies on the complete series demonstrate that photocyclization proceeds following a sequential ring closure mechanism. They clearly point out distinct quantum yields for the first and second ring closures, the latter being characterized by a significantly lower value. Dramatic decrease in both the quantum yields of the ring-closure and ring-opening processes is demonstrated for the complex L(d)ZnCl(2) exhibiting the strongest charge-transfer character in the series investigated. These studies show that this series of DTE derivatives provides an efficient strategy to tune the photochromic properties through the combination of the electron-donor and electron-acceptor (D-A) groups

A "reverse interrupter": the novel molecular design of a fluorescent photochromic DTE-based bipyridine

International audienceAn original design of a fluorescent dithienylethene (DTE)-based bipyridine, where donor (D) and acceptor (A) groups are located on the same thiophene ring of the DTE unit, is reported; in non-polar solvents, UV or visible excitation triggers a photochromic reaction, disrupting the conjugation and quenching the fluorescence

Influence of substituent modifications on the binding of 2-amino-1,8-naphthyridines to cytosine opposite an AP site in DNA duplexes: thermodynamic characterization

Here, we report on a significant effect of substitutions on the binding affinity of a series of 2-amino-1,8-naphthyridines, i.e., 2-amino-1,8-naphthyridine (AND), 2-amino-7-methyl-1,8-naphthyridine (AMND), 2-amino-5,7-dimethyl-1,8-naphthyridine (ADMND) and 2-amino-5,6,7-trimethyl-1,8-naphthyridine (ATMND), all of which can bind to cytosine opposite an AP site in DNA duplexes. Fluorescence titration experiments show that the binding affinity for cytosine is effectively enhanced by the introduction of methyl groups to the naphthyridine ring, and the 1:1 binding constant (106 M−1) follows in the order of AND (0.30) < AMND (2.7) < ADMND (6.1) < ATMND (19) in solutions containing 110 mM Na+ (pH 7.0, at 20°C). The thermodynamic parameters obtained by isothermal titration calorimetry experiments indicate that the introduction of methyl groups effectively reduces the loss of binding entropy, which is indeed responsible for the increase in the binding affinity. The heat capacity change (ΔCp), as determined from temperature dependence of the binding enthalpy, is found to be significantly different between AND (−161 cal/mol K) and ATMND (−217 cal/mol K). The hydrophobic contribution appears to be a key force to explain the observed effect of substitutions on the binding affinity when the observed binding free energy (ΔGobs) is dissected into its component terms

Chimie et physique de composes moleculaires bimetalliques: entites binucleaires, chaines ferrimagnetiques et aimants moleculaires

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 78314 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Etudes photophysiques de nanoparticules moléculaires photochromes et fluorescentes préparées par photofragmentation laser

Des nanoparticules (NPs) organiques photochromes (par réaction de cyclisation/cycloréversion entre une forme ouverte et une forme fermée) de diaryléthènes (P1 et PF1) ont été fabriquées par photofragmentation laser. La caractérisation des tailles et des propriétés photophysiques ont été effectuées par microscopie et spectroscopie (absorption UV-visible, DLS, AFM, MEB). Pour P1, l'influence de la fluence du laser et de la température sur la taille des NPs a été démontrée. Egalement, la compétition entre le photochromisme et la photofragmentation a été mise à profit pour contrôler la photofragmentation laser par la réaction photochrome. Une exaltation du rendement quantique de la réaction de cycloréversion par l'absorption à deux photons successifs a été montrée en solution. Dans le cas des NPs, la présence d un processus d'annihilation S1-S1 accentue cette exaltation. Concernant PF1, la dépendance en longueur d onde d excitation du rendement quantique de cycloréversion en solution a été démontrée et plusieurs conformations de la forme ouverte ont été identifiées. Les NPs de PF1 sont apparues comme un bon compromis entre la phase solide (fluorescente, non photochrome) et la solution (peu fluorescente, photochrome) : elles permettent une photocommutation efficace de la fluorescence. Une dépendance en taille des rendements quantiques de cyclisation/cycloréversion et des propriétés de fluorescence a été observée dans le cas des NPs. Le transfert d énergie intermoléculaire au sein des NPs permet d amplifier l extinction de fluorescence lors de la réaction photochrome. Ces résultats apportent des perspectives dans le stockage d'informations numériques de haute densité.Nanoparticles (NPs) of organic photochromic (cyclization/cycloreversion reaction between open and closed forms) materials (P1 and PF1) were prepared by the laser ablation method. Their size and their photophysical properties were investigated by microscopy and spectroscopy methods (UV-visible absorption, DLS, AFM, SEM). Regarding P1, the influence of the laser fluence and the temperature on the NPs size was evidenced. The competition between photochromism and ablation process was used to control the NPs formation by photochromism. An enhancement of the cycloreversion reaction occurred, via a stepwise two-photon absorption. In addition, in NPs, S1-S1 annihilation led to a further enhancement. Concerning PF1, a thorough study, involving quantum yields determination and DFT calculations was made. The cycloreversion quantum yield in solution shows an excitation wavelength dependence and several conformations of the open form were identified. NPs of PF1 were also prepared, and behave as a balanced trade-off between bulk (fluorescent, non photochromic) and solution (weakly fluorescent, photochromic): they allow an efficient photoswitching of the fluorescence. NPs size dependence of the cyclization/cycloreversion quantum yields and fluorescence properties was evidenced. The intermolecular energy transfer processes within the NPs enhances the fluorescence quenching during the photochromic reaction. These results are aimed to bring new perspectives results in the field of high-density digital information storage.CACHAN-ENS (940162301) / SudocSudocFranceF

Elaboration de couches minces de PZT (influence du procédé sur les propriétés physiques et structurales)

CACHAN-ENS (940162301) / SudocSudocFranceF

Spectroscopie transitoire et photo-commutation des propriétés optiques non linéaires de second ordre de cristaux photochromes d'anils, corrélation structure-propriétés

Une série d'anils originaux, de groupe d'espace non centrosymétrique actifs en génération de second harmonique (GSH) et photochromes à l'état cristallin, a été obtenue. Un des composés présente une GSH de 11 (vs urée), un deuxième une photo conversion de 16% sous irradiation UV et un troisième une quasi bistabilité (durée de vie de 460 j pour la forme métastable). La photo commutation réversible de la GSH peut aller jusqu'à 50%. Des études sur monocristaux orientés sous microscope confocal ont permis de corréler anisotropie de GSH et structure déterminée par diffraction de rayons X, via des calculs ZINDO. Elles ont aussi montré que la réaction photo induite créait un désordre dans le cristal, entraînant la commutation de GSH, mais que l'ordre initial était recréé après réaction retour. La spectroscopie a mis en évidence le mécanisme du photochromisme et un temps de commutation de 250 ps à l'état solide, montrant ainsi le potentiel de ces matériaux comme interrupteurs optiques rapides.A séries of original anils, crystallizing in a non centrosymmetric space group for second harmonic génération (SHG) and showing crystalline state photochromism was synthesized. One of them has an SHG intensity of 11 (vs urea), a second one shows a photo conversion of 16%, and a third one is a quasi bistable system (thé lifetime of thé métastable fonn is 460 days). Photo induced réversible SHG change can be up to 50%. Studies on single crystals performed on a confocal microscope allowed to correlate SHG anisotropy and thé structure determined by X ray diffraction connected with ZINDO calculations. Under UV irradiation, a structural disorder is created within thé crystal, responsible for thé SHG intensity change. However, thé initial structure is recovered alter thé reverse réaction. Spectroscopy evidenced thé mechanism of thé photochromism, and showed that switching occurred in 250 ps in solid state. This result demonstrates thé potentiality of such materials as fast optical switches.CACHAN-ENS (940162301) / SudocSudocFranceF

Photochromisme à l état solide (élaboration de nanomatériaux, propriétés de commutation, interactions avec des nanoparticules d or)

Ce travail présente d une part la fabrication d entités nanométriques (nanocouches, nanoparticules) photochromes et d autre part les méthodes de détection ou d amplification de leur commutation. Des nanoparticules de diaryléthène ont été obtenues par fragmentation laser. Leur caractère photochrome en solution colloïdale a été mis en évidence par des mesures d ensemble en spectroscopie d absorption, mais également au niveau de la particule unique par la spectroscopie de diffusion en champ sombre. Ces nanoparticules ont montré des propriétés différentes de celles en solution et de celles à l état solide illustrées par des rendements quantiques différents. Pour comparer les rendements quantiques des différents états, une méthode numérique a été mise au point pour l étude à l état solide. L obtention de systèmes hybrides par dépôt de couches minces de photochromes sur des substrats recouverts de nanoparticules d or a permis de mettre en évidence une nouvelle approche pour détecter la photocommutation aux petites échelles. Cette commutation du photochrome provoque un déplacement intense et réversible en longueur d onde de la bande des plasmons de surface localisée (PLS) des nanoparticules d or. Cette observation est corrélée à des calculs basés sur le formalisme de Mie. De plus, l exaltation du champ électromagnétique par excitation des PLS a permis d accélérer la réaction photochrome dans le sens de la décoloration, renforçant l intérêt de ces matériaux hybrides pour le stockage de données.This work deals with the design of photochromic nanoobjects (nanolayers, nanoparticles) and with new approaches to detect and enhance photoswitching. Nanoparticles have been obtained by laser ablation technique. Their photochromic properties have been demonstrated in colloidal solution using conventional absorption spectroscopy and at the single particle level using dark-field scattering microscopy. These nanoparticles exhibits quantum yields which are different from those determined in the solution and the solid state. In order to compare these quantum yields, a home-made software have been used for the solid state. Hybrid nanoscale layers with gold nanoparticles and photochromic compounds have been obtained by vacuum deposition technique of diarylethene on gold covered substrate. A reversible shift of the plasmon band induced by the photochromic reaction is correlated to calculation based on Mie formalism. The switchable plasmon shift is particularly interesting in order to allow detection at very low level. Besides, the enhancement of the electromagnetic field has induced the acceleration of the photochromic reaction to the colorless form, thus demonstrating the interest of these hybrid materials for data storage.CACHAN-ENS (940162301) / SudocSudocFranceF

Long-term shifts in the growth and maturation size of Miyabe charr Salvelinus malma miyabei

Overfishing can affect life history traits, resulting in population collapse and oftentimes a decrease in length-at-age and maturation size in fish populations. However, little is known about the recovery mechanisms and time scales of these traits in exploited wild populations. In the study reported here, we documented long-term shifts in growth and mature size in Miyabe charr Salvelinus malma miyabei associated with a history of recreational fishing in Lake Shikaribetsu for approximately 80 years. Downsizing in the charr was observed when the charr population collapsed due to intensive recreational fishing. However, subsequent moratoriums and the introduction of fishing regulations, especially the implementation of a catch-and-release policy, during the following 10-30 years facilitated the recovery of population size, length-at-age and mature fish size. This study provides important insights into the biological changes and required recovery time scales of a heavily harvested population and supports management and conservation strategies.北海道然別湖に生息するミヤベイワナの成長解析を行い、約80年にわたる漁獲圧と成長や成熟魚サイズの変化の関係について検討した。その結果、過剰な遊漁による漁獲圧の上昇により、ミヤベイワナの成長が鈍化し成熟魚が小型化したと考えられた。しかし、禁漁や遊漁規制の導入により、現在は乱獲状態にあった時期と比べて資源が回復し、約10年から30年で個体の成長と成熟魚サイズが回復したことが示唆された