Laser nanosources based on planar photonic crystals as new platforms for nanophotonic devices

Two-dimensional photonic crystal lasers have been fabricated on III–V semiconductor slabs. Tuning of the spontaneous emission in micro and nanocavities has been achieved by accurate control of the slab thickness. Different structures, some of them of new application to photonic crystal lasers, have been fabricated like the Suzuki-phase or the coupled-cavity ring-like resonators. Laser emission has been obtained by pulsed optical pumping. Optical characterization of the lasing modes have been performed showing one or more laser peaks centred around 1.55 μm. Far field characterization of the emission pattern has been realized showing different patterns depending on the geometrical shape of the structures. These kinds of devices may be used as efficient nanolaser sources for optical communications or optical sensors.     

Ab initio X-ray powder diffraction characterisation of molecule-based magnetic materials

Use of ab initio X-ray powder diffraction (XRPD) methods in the study of magnetically active species of covalent nature is presented. Selected cases are chosen in order to underline the power of XRPD methodologies, highlighting the importance of independent physico-chemical information from ancillary techniques.     

2H NMR spectra of 2-(p-heptylbenzoyloxy)-5-(p-heptylbenzenazo)tropone. A new sigmatropic liquid crystal

Liquid crystals incorporating in their molecular framework a seven-membered ring are still relatively rare [1]. Recently the synthesis and thermal behaviour of a series of liquid crystal materials having a tropone moiety in their mesogenic core have been reported [2-4]. These mesogens, based on a 2-(acyloxy)tropone core structure, show intramolecular migration of the acyl substituents between the two oxygen atoms at C-1 and C-2, an effect already known for simple 2-(acyloxy)tropones in their isotropic solutions [5]. This migration involves a concerted [1, 9]-sigmatropic rearrangement [2]. This rearrangement could play a major role in determining the properties of the mesophases: it has been suggested in fact that, because of this rearrangement, the mesogenic molecules acquire a mean rod-like shape which can sustain the mesophase formation [2].     

RADICAUX LIBRES INDUITS PAR L''ACTION DU RAYONNEMENT ULTRAVIOLET SUR CERTAINS CONSTITUANTS DE L''ACIDE DEOXYRIBONUCLEIQUE

The action of ultra violet rays of 260 nm on aqueous solutions of bases, nucleosides and nucleotides of DNA at 77°K is studied by electron spin resonance. It is shown that the free radicals observed are similar, with a few noteworthy exceptions to those induced by X-rays, under the same conditions of temperature, in the solid state. Contrary to what might be excepted on the basis of the results obtained by X-rays, the variation in the yield in paramagnetic centres in each sequence studied does not seem to be important.     

2-(2-Hydroxyaryl)cinnamic amides: a new class of axially chiral molecules

The syntheses of several differently substituted amides formally derived from a chiral amine, either E-2-(2-hydroxyphenyl)cinnamic acid or both E- and Z-2-(2-hydroxynaphthyl)cinnamic acid, are reported. These molecules display a restricted rotation about the C₂-C_aryl bond. The barriers to rotation about the C₂-C_aryl bond were measured by the dynamic ¹H NMR and were found to vary between 11.8 and 24.5 kcal mol⁻¹, depending on the substitution. In particular, E-2-(2-hydroxynapthyl)cinnamic amides, displayed a high barrier to rotation (ΔG_c^‡=24.4 kcal mol⁻¹) and could be isolated in both diastereomerically pure forms at room temperature. The X-ray structure of one E-2-(2-hydroxynapthyl)cinnamic amide, was resolved, enabling for the determination of the absolute configuration of the chiral axis (aR).     

ETUDE PAR RESONANCE PARAMAGNETIQUE ELECTRONIQUE DE LA PHOTOSENSIBILISATION DES ACIDES AMINES PAR LA PROFLAVINE

Abstract— –The photosensitization of amino acids by proflavine is studied using the technique of electron spin resonance spectroscopy. The analysis of the line shape as a function of the incident microwave power (both in the presence and absence of oxygen) and the dependence of the numbers of free radicals on the intensity of the incident light allow one to suggest that two types of radicals are formed. One is formed by a biphotonic process, the nature of the radicals being the same as in the case of ionising radiation, while the other is probably the RO₂ radical formed as a result of photodynamic action.     

Optically activated functionalization reactions in Si quantum dots

Using ab initio calculations, we have studied the influence of optical activation on functionalization reactions of silicon quantum dots with unsaturated hydrocarbons. We find that the energy barrier for the replacement of silicon-hydrogen with silicon-carbon bonds is dramatically reduced if the silicon dot is optically excited. These results provide an explanation for recent experiments on optically excited porous silicon. In addition, our calculations point at the existence of an intermediate spin-polarized state formed by the dot and an alkene or alkyne, upon relaxation after absorbing a photon. This state could be detected experimentally, by, for example, electron spin resonance measurements. Based on the results of our calculations as a function of the dot size, varied from 0.8 to 1.5 nm, we propose that light activated reactions could be used to functionalize and size select silicon quantum dots at the same time.     

A Popov-theory-based approach to digital H{infty} control with measurement feedback for Pritchard-Salamon systems

In this paper, we deal with the digital output-measurement-feedbackH control problem for Pritchard-Salamon infinite-dimensionalsystems with unbounded input and output operators. A discretePopov-theory-based solution is given in terms of the solvabilityof Kalman-Szegö-Popov-Yakubovitch systems associated withthe equivalent discrete-time time-invariant system obtainedby lifting the T-periodic continuous-time system.