30 research outputs found
Porosity-driven large amplitude dynamics for nitroaromatic sensing with fluorescent films of alternating D-π-A molecules
International audienceWe report herein the structural properties and nitroaromatic sensing performances of fluorescent thin films formed by alternating donor-acceptor pi-conjugated chromophores. The incorporation of a flexible one-dimensional alkyl chain in the chromophore backbone drastically accelerates by more than one order of magnitude the sensing dynamics for the detection of 2,4-dinitrotoluene (DNT) vapors
Generating long supra-molecular pathways with a continuous density of states by physically linking conjugated molecules via their end-groups
International audienceSelf-assembly of conjugated 2,5-dialkoxy-phenylene-thienylene-based oligomers on epitaxial monolayer graphene was studied in ultrahigh vacuum by low-temperature scanning tunneling microscopy (STM). The formation of long one-dimensional (1D) supramolecular chain-like structures has been observed, associated to a physical linking of their ends which involved the rotation of the end thiophene rings in order to allow π–π stacking of these end-groups. dI/dV maps taken at an energy corresponding to the excited states showed a continuous electronic density of states, which tentatively suggests that within such molecular chains conjugation of electrons is preserved even across physically linked molecules. Thus, in a self-organization process conjugation may be extended by appropriately adapting conformations of neighboring molecules. Our STM results on such self-organized end-linked molecules potentially represent a direct visualization of J-aggregates
STM Studies of Self-Assembled Tetrathiafulvalene (TTF) Derivatives on Graphene: Influence of the Mode of Deposition
The
conformations and the self-assembly process of tetrathiafulvalene
(TTF) derivatives functionalized by lateral alkylthio chains deposited
on graphene/SiC(0001) in ultrahigh vacuum (UHV) and at the solid–liquid
interface are studied by scanning tunneling microscopy (STM). The
study in UHV evidences a “molecular fastener” effect
induced by the increase of van der Waals interactions between the
alkylthio side chains which forces the major part of the molecules
to self-organize in π–π stacked edge-on conformation.
The study at the solid–liquid interface reveals a drastically
different behavior with molecules lying flat on the surface as the
solvent is involved in the stabilization of the molecular layer. This
work raises a burning issue concerning the choice of the deposition
method for graphene functionalization with such molecules
Highly n-doped graphene generated through intercalated terbium atoms
We obtained highly n-type doped graphene by intercalating terbium atoms between graphene and SiC(0001) through appropriate annealing in ultrahigh vacuum. After terbium intercalation angle-resolved-photoelectron spectroscopy (ARPES) showed a drastic change in the band structure around the K points of the Brillouin zone: the well-known conical dispersion band of a graphene monolayer was superposed by a second conical dispersion band of a graphene monolayer with an electron density reaching 10(15) cm(-2). In addition, we demonstrate that atom intercalation proceeds either below the buffer layer or between the buffer layer and the monolayer graphene. The intercalation of terbium below a pure buffer layer led to the formation of a highly n-doped graphene monolayer decoupled from the SiC substrate, as evidenced by ARPES and x-ray photoelectron spectroscopy measurements. The band structure of this highly n-doped monolayer graphene showed a kink (a deviation from the linear dispersion of the Dirac cone), which has been associated with an electron-phonon coupling constant one order of magnitude larger than those usually obtained for graphene with intercalated alkali metals
One- and two-photon absorption and emission properties of an oligo(phenylenethienylene)s series
International audienceThe photophysical and nonlinear absorption properties of an oligo(phenylenethienylene)s series (nTBT) are investigated in this article. The length of the chromophore is gradually increased from one to four phenylenethienylene repeating units in order to evaluate the effects of the electronic delocalization on the two-photon absorption cross sections (δ). According to the excitation anisotropy measurements and quantum chemical calculations, two electronic transitions with distinctive symmetries, 1Ag → 1Bu and 1Ag → 2Ag, are present in the low energy region of the linear absorption spectrum. The lowest-energy transition 1Ag → 1Bu is one-photon allowed but two-photon forbidden and implies an electronic charge delocalization all along the oligomer segment whereas the weakly-allowed 1Ag → 2Ag transition exhibits a transition moment perpendicular to the average plane of the chromophore. The latter transition mainly contributes to the two-photon absorption ability of the oligomers. All derivatives are poorly solvatochromic and the breakdown of the mirror symmetry rule observed between absorption and fluorescence spectra at room temperature has been attributed to a photoinduced geometrical relaxation leading to a very efficient planarization process of the oligomer irrespective of its size. Increasing the oligomer length results in a slight shift of the two-photon absorption band ([similar]1300 cm−1) and in a drastic increase of δ from 2 ± 1 GM up to 802 ± 160 GM for 1TBT and 4TBT respectively. Based on a three-level model, it was found that main contributions to the strong increase of δ stem from the transition moments Mge and Mee′ which are multiplied by a factor of 2.8 and 5 when going from 1TBT to 4TBT
Strategies for the prevention of hip fracture
Hip fractures are associated with 10% to 20% excess mortality in the first year and cause functional disability in most survivors. An estimated 17% of white women in the United States will sustain a hip fracture after the age of 50 years. Despite the availability of evidence-based guidelines for hip fracture prevention, routine screening and preventive measures have not been incorporated into standard primary care practice. Many physicians lack adequate knowledge to initiate bone mineral density testing and treatment with preventive medications to decrease the incidence of osteoporosis and fractures. Furthermore, patients are less likely to request information about bone health than about diseases for which systematic screening and prevention protocols have been established. This review describes preventive measures to decrease hip fracture in postmenopausal women, including screening by bone mineral density testing, risk factor assessment, and chemoprevention. Existing guidelines are summarized, and dilemmas regarding their implementation are discussed. (C) 2003 by Excerpta Medica Inc
Cost effectiveness of denosumab compared with oral bisphosphonates in the treatment of post-menopausal osteoporotic women in Belgium
Porosity-driven large amplitude dynamics for nitroaromatic sensing with fluorescent films of alternating D–π–A molecules
Evidence-based guidelines for the treatment of postmenopausal osteoporosis: a consensus document of the Belgian Bone Club
SCOPUS: cp.jinfo:eu-repo/semantics/publishe