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

Synthesis and characterization of the ground and excited states of tripodal-like oligothienyl-imidazoles

Six new thiophene oligomers, here designated as tripodal-like oligothienyl imidazoles, were synthesized and have been investigated in ethanol solution at room and low temperature. The oligomers bear a common core where two or more thiophenes are linked to one or more imidazole unit which further links through its alpha position to a different number of incremental thiophene units. The study involves a comprehensive spectral and photophysical investigation where the properties of the singlet and triplet states have been investigated regarding absorption, fluorescence and phosphorescence, transient triplet-triplet absorption together with all relevant quantum yields (fluorescence, internal conversion, intersystem crossing and singlet oxygen) and lifetimes. In addition, DFT quantum chemical calculations were performed to gain a detailed understanding of the molecular geometry and optical properties of the investigated oligomers. From the overall data, the radiative (kF) and radiationless (kNR, kIC and kISC) rate constants have been determined and it is shown that, in contrast with the parent oligothiophenes, the radiative competes with the radiationless deactivation channels. The results show that, by comparison with the oligothiophene counterparts, there is an augment of the relative contributions of the internal conversion and fluorescence processes relative to the S1~~T1 intersystem crossing. Phosphosphorescence emission was found for the simplest member of the investigated compounds, with a low quantum yield and a lifetime of 8 picos. The data also show that the introduction of a 4,5-dithienyl-imidazole moiety in a bi- or terthiophene oligomer results in, respectively, a 20-fold and a 3-fold increase of the fluorescence quantum yield relative to their oligothiophene counterparts.Fundação para a Ciência e a Tecnologia (FCT