Characterization of a sensitive and selective copper optode based on ß-ketoimine modified calix[4]arene derivative.

In this paper, an optical sensor was proposed for sensitive determination of copper (II) ions in aqueous solution. The sensing membrane was prepared by coating ß-ketoimine calix[4]arene derivative as ionophore on a glass plate surface. Thin ß-ketoimine calix[4]arene layer was characterized by contact angle measurements showing a good surface coverage. Besides, a smooth and homogeneous morphology of the calixarene membrane was examined by atomic force microscopy (AFM). The response of the optode is based on the decrease in the absorbance signal at 309 nm upon exposure to buffer solutions containing Cu(2+) ions. At a pH 6.8, the proposed sensor displays a calibration response for copper over a wide concentration range of 1.0×10(-7) M to 1.0×10(-4) M with a detection limit of 2.0×10(-8) M and response time of 7-10 min. This optode exhibits good selectivity toward copper ions in comparison with common ions including Hg(2+) and Ag(+) ions. The copper sensing film can be regenerated using 0.01M HNO3 solution. In addition to its high stability, repeatability and reproducibility, the sensor shows operational life time of 4 weeks.

Time resolved and temperature dependence of the radiative properties of thiol-capped CdS nanoparticles films.

In this work, we present the temperature-dependence and time-resolved photoluminescence (PL) of CdS nanoparticles capped independently with three different ligands thiophenol, thioglycerol, and l-cysteine over a broad temperature range from 10 to 300 K. The respective nanoparticles sizes in the three systems studied in this work are 1.5, 4, and 2 nm as determined from X-ray diffraction (XRD). From the analysis of AFM images, it was found that the lateral particle sizes of capped CdS nanoparticles are greater than those deduced from XRD or optical absorption measurements. The aim of this study is the investigation of the impact of the organic ligands on the radiative recombination dynamics in organically capped CdS nanoparticles. From the PL study and based on the temperature-dependence and time-resolved emission spectroscopy, we conclude that the emission of CdS QDs film originates from recombination of the delocalized carriers in the internal core states with a small contribution of the localized carriers at the interface. The PL decay reveals a biexponential behavior for the entire three samples at all temperatures. One of the two exponential components decays rapidly with a time τ1 in the range 0.5-0.8 ns, whereas the other decays much more slowly, with a time τ2 in the range 1-3 ns. The weak activation energy (32-37 meV) deduced from the temperature dependence of the PL intensity suggests the involvement of shallow traps. The analysis of the experimental results reveals a relatively narrow size distribution, an efficient surface passivation, and a satisfactory thermal stability of CdS nanocrystals.

Studies of aluminum (III) ion-selective optical sensor based on a chromogenic calix[4]arene derivative.

An optical chemical sensor based on azo-calix[4]arene derivative is developed for the determination of aluminum (III) ions in aqueous solutions. The complex formation ability of azo-calix[4]arene toward metal cations such as Li(I), Cs(I), K(I), Sn(II), Pb(II), Cu(II), Eu(III), Er(III) and Al(III) is investigated by UV-vis spectroscopy. Assessments of results reveal that the azo-calix[4]arene derivative has high affinity to Al(III). The stoichiometric ratio and the association constant were determined as 1:1 and 1.24×10(4)M(-1), respectively for the complex between Al(3+) and the azo-calix[4]arene. The sensing film is fabricated by spin coating on glass plates. Under the optimized conditions, at pH 6.8, the proposed optical sensor displays a linear response to Al(3+) over 10(-7) to 10(-5)M range with response time of 12min. The optical sensor can be regenerated with HNO3 solution. In addition to its high stability and reproducibility, the sensor shows good selectivity for Al(3+) ion.

Structural and spectroscopic study of the LiRb molecule beyond the Born-Oppenheimer approximation.

Adiabatic and diabatic potential energy curves and the permanent and transition dipole moments of the low-lying electronic states of the LiRb molecule dissociating into Rb(5s, 5p, 4d, 6s, 6p, 5d, 7s, 6d) + Li(2s, 2p) have been investigated. The molecular calculations are performed with an ab initio approach based on nonempirical pseudopotentials for Rb(+) and Li(+) cores, parametrized l-dependent core polarization potentials and full configuration interaction calculations. The derived spectroscopic constants (R(e), D(e), T(e), ω(e), ω(e)x(e), and B(e)) of the ground state and lower excited states are in good agreement with the available theoretical works. However, the 8-10(1)Σ(+), 8-10(3)Σ(+), 6(1,3)Π, and 3(1,3)Δ excited states are studied for the first time. In addition, to the potential energy, accurate permanent and transition dipole moments have been determined for a wide interval of internuclear distances. The permanent dipole moment of LiRb has revealed ionic characters both relating to electron transfer and yielding Li(-)Rb(+) and Li(+)Rb(-) arrangements. The diabatic potential energy for the (1,3)Σ(+), (1,3)Π, and (1,3)Δ symmetries has been performed for this molecule for the first time. The diabatization method is based on variational effective Hamiltonian theory and effective metric, where the adiabatic and diabatic states are connected by an appropriate unitary transformation.

Theoretical study of the LiCs molecule: adiabatic and diabatic potential energy and dipole moment.

For nearly all the states dissociating into Cs (6s, 6p, 5d, 7s, 7p, 6d, 8s) and Li (2s, 2p, 3s), we present an extensive adiabatic study for (1,3)Sigma(+), (1,3)Pi, and (1,3)Delta symmetries of the LiCs molecule. We have used an ab initio approach based on nonempirical pseudopotentials, parametrized l-dependent polarization potentials, and full configuration interaction calculations. A diabatisation procedure based on the effective Hamiltonian theory and an effective metric is used to produce the quasi-diabatic potential energy for all studied states. The spectroscopic constants (R(e), D(e), T(e), omega(e), omega(e)x(e), and B(e)) of these states are derived and compared with the available theoretical and experimental works. In addition to the potential energies, accurate permanent and transition dipole moment have been determined for a wide range of internuclear distances. The adiabatic permanent dipole moment for the first 10 (1)Sigma(+) electronic states has revealed ionic characters relating to electron transfer and yielding both Li(-)Cs(+) and Li(+)Cs(-) arrangements. The quasi-diabatic permanent moments show linear behaviors, especially at intermediate and large distance. The transition dipole moment between neighbor states has revealed many peaks located around the avoided crossing positions.

Investigation of exciton photodissociation, charge transport and photovoltaic response of poly(N-vinyl carbazole):TiO(2) nanocomposites for solar cell applications.

The photogeneration of charge carriers in spin-coated thin films of nanocrystalline (nc-)TiO(2) particles dispersed in a semiconducting polymer, poly(N-vinylcarbazole) (PVK), has been studied by photoluminescence and charge transport measurements. The solvent and the TiO(2) particle concentration have been selected to optimize the composite morphology. A large number of small domains leading to a large interface and an improved exciton dissociation could be obtained with tetrahydrofuran (THF). The charge transport mechanism and trap distribution at low and high voltage in ITO/nc-TiO(2):PVK/Al diodes in the dark could be identified by current-voltage measurements and impedance spectroscopy. The transport mechanism is space charge limited with an exponential trap distribution in the high voltage regime (1-4 V), whereas a Schottky process with a barrier height of about 0.9 eV is observed at low bias voltages (<1 V). The current-voltage characteristics under white illumination have shown a dramatic increase of the short circuit current density J(sc) and open circuit voltage V(oc) for a 30% TiO(2) volume content corresponding to the morphology exhibiting the best dispersion of TiO(2) particles. A degradation of the photovoltaic properties is induced at higher compositions by the formation of larger TiO(2) aggregates. A procedure has been developed to extract the physical parameters from the J-V characteristics in the dark and under illumination on the basis of an equivalent circuit. The variation of the solar cell parameters with the TiO(2) composition confirms that the photovoltaic response is optimum for 30% TiO(2) volume content. It is concluded that the photovoltaic properties of nc-TiO(2):PVK nanocomposites are controlled by the interfacial area between the donor and the acceptor material and are limited by the dispersion of the TiO(2) nanoparticles in the polymer.