Andréa Monteiro Santana Silva

Theoretical nonlinear optics equivalence between mesoionic and polyenic bridges in push-pull compounds

In this work we report a semiempirical investigation with the purpose of establishing an equivalence in terms of the value of the first static hyperpolarizability, b(0), of push-pull compounds of the type electron-acceptor(A) - bridge - electron-donor(D), either formed by polyenic bridges or by mesoionic bridges, keeping unchanged both D and A groups. The ground state geometries of the molecules were optimized via AM1 using Mopac93r2 program. The value of b(0) was calculated by time-dependent Hartree-Fock (TDHF). Our results indicate that a bridge formed by a single mesoionic ring can be equivalent to seven or more conjugated double bonds, depending on the ring, reaffirming that mesoionic rings constitute promising materials for photonics applications.

Photovoltaic Response of Ultrathin Films of Retinal Derivatives

Langmuir-Blodgett mixed films of retinal derivatives and fatty acids deposited on conducting glass slides were used in the present study of the photovoltaic response of retinal derivatives. The presence of incident light can affect the compression isotherms of the Langmuir films of cis and trans retinal in a distinct manner by changing the intrinsic organization of the floating monolayer, and a definite difference in the photovoltaic response of the corresponding ultrathin films of retinal derivatives is observed.

Sensores ópticos com detecção no infravermelho próximo e médio

Optical chemical sensors with detection in the near and mid infrared region are reviewed. Fundamental concepts of infrared spectroscopy and optical chemical sensors are briefly described, before presenting some aspects on optical chemical sensors, such as synthesis of NIR and IR reagents, preparation of new materials as well as application in determinations of species of biological, industrial and environmental importance.

Ultrathin Conducting Polymer Films as Sensors of Volatile Compounds

The self-assembly technique was used to prepare polymeric thin films composed of bilayers of polypyrrole (PPY) doped with different counter-ions and poly(3-thiophene acetic acid) (PTAA), directly on conducting glass electrodes. The electrical conductivity of these thin films - which have a relative high degree of structural order and large surface to volume ratio - responds in a very fast manner to the exposure to vapors of simple organic solvents (methanol, ethanol, carbon tetrachloride and benzene). The changes in the fractional difference of individual films disposed as an sensor array were measured and the Principal Components Analysis (PCA) was used to correlate the corresponding collective pattern to the specific volatile compound.

Evaluation of a PVC sensing phase for determination of chlorinated hydrocarbons in water by mid-infrared spectroscopy

In this work, mid-infrared spectroscopy has been employed to investigate the effect of amount (25 or 40%) and type of plasticiser (di-2-ethylhexyl sebacate (DOS), di-2-ethylhexyl phthalate (DOP) and 2-nitrophenyl octyl ether (NPOE)) on the analytical response of a poly(vinylchloride) (PVC) sensing phase for the determination of the chlorinated hydrocarbons (chlorobenzene (ClB), trichloroethylene (TCE) and trichlorobenzene (TCB)) in water. It was observed that films with 40% of plasticiser provided higher sensitivity and lower limits of detection than those with 25%, although the later films are easier to handle. A similar behaviour was also observed for sensing phases prepared with the plasticisers NPOE and DOS. By employing a DOS-based PVC sensing phase and extraction time of 60 min, limits of detection of 0.3, 0.6, and 0.5 mg L-1 were obtained for chlorobenzene, trichloroethylene and trichlorobenzene, respectively.