Helically chiral functionalized [6]helicene: Synthesis,optical resolution,and photophysical properties

A short and efficient synthetic pathway leading to a new chiral π-conjugated system is reported. The X-ray structure of the target compound was determined and showed a helical conformation. Its resolution was successfully accomplished, leading to two enantiomers in high optical purity, and their chiroptical properties were examined experimentally. The photophysical properties of the organic material were also evaluated, showing an emission in the visible region, and HOMO and LUMO levels have been estimated experimentally, demonstrating an electrochemical band gap of 2.37 eV.     

Highly sensitive modified glassy carbon sensor based on TDAN for nitrate detection in real water

Glassy carbon electrodes modified with a plasticized PVC membrane including tetradodecyl ammonium nitrate (TDAN) and two different plasticizers [bis(2-etheylhexyl) sebacate (DOS) and dibutyl phthalate (DBP)]. TDAN is a quaternary ammonium salt, used in nitrate-selective field-effect transistor membrane, and it is applied as an ionophore for sensor development. Membranes were prepared as sensing matrix for nitrate detection through the intensity of its reduction peak using cyclic voltammetry. Under optimum conditions, the detection limits of nitrate obtained with TDAN + DOS and TDAN + DBP, are 10–6 mol/dm3 and 10–9 mol/dm3, respectively. As a result, the developed sensors based on TDAN + DOS and TDAN + DBP matrices demonstrate satisfactory quantified amounts in determination of nitrate in water where the measured values were less than 0.57 × 10–7 mol/dm3 and 0.73 × 10–10 mol/dm3, respectively.     

Synthesis and Characterization of New Variously Substituted Allylic Phosphates

New allylic phosphates were synthesized through phosphorylation of the corresponding alcohols. These compounds were obtained as mixtures of two (Z and E) isomers in 55–85% yield. They were characterized by multinuclear (¹H, ¹³C, ³¹P, and ¹⁹F) NMR, IR spectroscopy, and HRMS.     

Use of microwaves in thermal analysis

Introduction of microwaves in thermal analysis techniques may solve gradient problems and enlarge the investigation possibilities of thermal analysis. A microwave power control set up in our laboratory provides the sample with a constant and well defined heating rate. Experimental set used for DTA is described. Differential thermal curves got for some mineral products showing exothermal water departure peaks are compared to conventional DTA curves got for the same materials. Thermodilatometric curves of PVC realized with the same apparatus, under microwave and standard heating, show that transformations appear more clearly than under conventional heating. A transformation which almost is not discernible under conventional heating is clearly evidenced. As transformation temperatures under microwaves appear at lower values in DTA as in thermodilatometry, it looks probable that a part of the absorbed microwave energy enters under an other form than heat.

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Zusammenfassung Die Einführung von Mikrowellen in thermische Analysentechniken kann Gradientenprobleme lösen und die Aussagemöglichkeiten der thermischen Analyse vergrößern. Ein in unserem Laboratorium eingesetzter Mikrowellengenerator ermöglicht die Aufheizung der Probe mit konstanter und gut definierter Geschwindigkeit. Eine zur DTA benutzte Versuchsanordnung wird beschrieben. Die für einige mineralische Substanzen mit exothermen Wasserangabepeak erhaltenen DTA-Kurven werden mit den konventionellen DTA-Kurven der gleichen Materialien verglichen. In mit der gleichen Apparatur aufgenommen thermodilatometrischen Kurven von PVC sind bei Anwendung der Mikrowellenheizung Umwandlungen klarer zu erkennen als bei der herkömmlichen Verfahrensweise. Eine bei konventionellen Aufheizen meist nicht erkennbare Umwandlung wird klar nachgewiesen. Da bei Mikrowellenheizung die Umwandlungstemperatur bei DTA-Versuchen niedriger als bei thermodilatometrischen Experimenten liegen, erscheint es als wahrscheinlich, daß ein Teil der absorbierten Mikrowellenenergie in einer anderen Form als in der von Wärme aufgenommen wird.

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Short and long consecutive pairs model in the interpretation of MFE and F-ODMR experiments in molecular crystals

We have presented a model of two consecutive pairs of triplet excitons, which consists of a succession of two pairs known as short pair and long pair with reference to their respective lifetimes. We have applied this model to the modulation of prompt fluorescence (PF) in crystalline tetracene by a static magnetic field (MFE) and a microwave field (F-ODMR). The two types of experiments have been enough perfectly reproduced by using the same set of kinetics constants. Thus, we have arrived to rise the inconsistencies which one reproached the Seventies kinetic model.     

Triplet-triplet interaction in a nearly one dimensional molecular crystal: Application to 1,4-dibromonaphtalene

The effect of a magnetic field (6 kG) on the delayed fluorescence in a 1,4-Dibromonaphtalene at 300 K and 20 K is analysed using a new approach of calculation of the triplet-triplet annihilation rate constant. The agreement of the best fit between experiment and theory allows reaching at 300 K and 20 K respectively the lifetimes and the interaction constant of the triplets pairs. Received 12 March 1999 and Received in final form 27 April 2000