Photochemistry and photophysics of thienocarbazoles

Two methylated thienocarbazoles and two of their synthetic nitro-precursors have been examined by absorption, luminescence, laser flash photolysis and photoacoustic techniques. Their spectroscopic and photophysical characterization involves fluorescence spectra, fluorescence quantum yields and lifetimes, and phosphorescence spectra and phosphorescence lifetimes for all the compounds. Triplet-singlet difference absorption spectra, triplet molar absorption coefficients, triplet lifetimes, intersystem crossing S-1 similar tosimilar to--> T-1 and singlet molecular oxygen yields were obtained for the thienocarbazoles. In the case of the thienocarbazoles it was found that the lowest-lying singlet and triplet excited states, S, and T-1, are of pi,pi* origin, whereas for their precursors S-1 is n,pi*, and T-1 is pi,pi*. In both thienocarbazoles it appears that the thianaphthene ring dictates the S, T, yield, albeit there is less predominance of that ring in the triplet state of the linear thienocarbazole, which leads to a decrease in the observed Phi(T) value.info:eu-repo/semantics/publishedVersio

Neural Online Filtering Based on Preprocessed Calorimeter Data

Aiming at coping with LHC high event rate, the ATLAS collaboration has been designing a sophisticated three-level online triggering system. A significant number of interesting events decays into electrons, which have to be identified from a huge background noise. This work proposes a high-efficient L2 electron / jet discrimination algorithm based on artificial neural processing fed from preprocessed calorimeter information. The feature extraction part of the proposed system provides a ring structure for data description. Energy normalization is later applied to the rings, making the proposed system usable for a broad energy spectrum. Envisaging data compaction, Principal Component Analysis and Principal Component of Discrimination are compared in terms of both compaction rates and classification efficiency. For the pattern recognition section, an artificial neural network was employed. The proposed algorithm was able to achieve an electron detection efficiency of 96% for a false alarm of 7%

Synthesis and photophysical characterization of novel triphenylamine-benzimidazole derivatives

Research on organic luminescent materials has been intensely pursued due to their importance in technological applications related to signaling, fluorescent biosensory/chemosensory materials, molecular switches and organic light emitting diodes (OLEDs). Organic fluorophores such as triphenylamine and benzimidazole derivatives have attracted a particular attention owing to their high emission efficiency being widely used as electron transporters and emitting layers for OLEDs.1 Recently, we have been investigating the potential of heterocyclic systems bearing functionalized (benz)imidazole derivatives exhibiting high thermal stability, interesting emissive and chemosensory properties.2 In this communication we report the synthesis and photophysical characterization of triphenylamine-benzimidazoles (compounds 1a-d) which were synthesized by a one step reaction through the Na2S2O4 reduction of several commercially available o-nitroanilines in the presence of triphenylamine aldehyde in DMSO at 120 °C. Compounds 1a-d bear different functionalization at position 5 of the benzimidazole with electron-donor or acceptor groups (Figure 1). A comprehensive spectral and photophysical investigation of these compounds including absorption, fluorescence and triplet-triplet absorption spectra, together with quantum yields of fluorescence, internal conversion, intersystem crossing and singlet oxygen and rate constants for the radiative and radiationless processes has been undertaken in solution at room temperature. It is shown that compounds 1a-d exhibit high fluorescence quantum yields (0.70-0.78). Additionally, a comparison between the optical and photophysical properties of 1a-d will be also presented and discussed.Fundação para a Ciência e a Tecnologia (FCT

Comportamento de algumas gramíneas forrageiras em solo de pastagem degradada de Paragominas-PA.

bitstream/item/57472/1/CPATU-ComTec58.pd

Fluorescence Enhancement of the Water- Soluble Poly{1,4-phenylene-[9,9-bis- (4-phenoxybutylsulfonate)]fluorene-2,7-diyl} Copolymer in n-Dodecylpentaoxyethylene Glycol Ether Micelles

http://dx.doi.org/10.1021/ma048780

The chemistry behind the first Portuguese postage stamps (1853–1894). A non-destructive analytical and chemometric analysis of pigments, fillers and binders

The analysis of 28 specimens of some of the first Portuguese postage stamps, dated from 1853 to 1894, was undertaken with non-destructive techniques: X-Ray fluorescence (XRF), Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) and Ultraviolet–Visible Reflectance Spectroscopy (UV–Vis). Ink, paper and cancellation of the postage stamps were analysed, and the pigments, binders and fillers identified. Prussian blue was found present in all blue and also in green and brown specimens. Chrome and zinc yellow, lead sulphate and mars red were also found in other of the investigated postage stamps. Binders consist mostly of protein glue. Fillers such as calcite and kaolinite were found dominant. The presence of the latter served as an indicator for distinguishing between genuine and forged samples. UV–Vis spectra also proved useful for the same purpose. All the above information was processed and organized using chemometric techniques. These include mainly Hierarchical Cluster Analysis (HCA), for clustering stamps of similar composition, and Principal Component Analysis (PCA) for mapping the samples and identifying the more relevant variables. The latter are, in the paper, content of calcium, potassium, sulphur and silicon and, in the dye pigment area, of iron, zinc and lead content. The study introduces an approach in which, by combination of non-destructive multi analytical techniques with chemometric analysis, extensive information on different aspects of the composition of the studied postage stamps is provided, including that of paper and dyes