Optical gap energy study of poly(thienylene-2,5-dialkoxyphenylene) in solid-state films

Optical gap energy (E_gap) in luminescent π-conjugated polymers presents several difficulties in its determination, particularly when using CW conventional optical spectroscopy, absorption and emission. This happens due to several physicochemical parameter's dependence. Among others, the molecular conformation, intramolecular interactions, structural defects, polymer processability and solvent interaction stand out. In addition, there is a distribution of conjugated segments along the polymeric main chains that differentiate optical absorption transition from emission processes. In other words, these processes do not necessarily occur in the same conjugated segment owing to the very efficient ratios of energy transfer or charge migration in these materials. In this work we present a systematic study of the determination of E_gap for the polymer poly(thienylene-2,5-dialkoxyphenylene). We present a comparison between the solution and solid-state film, clearly showing the presence of a polymer-polymer interaction as aggregate species. The goal of this paper is to isolate and aggregate the contribution determination of each species through systematic analysis of optical spectra, as well as to obtain, even on film, the E_gap of the isolated polymer which is very similar to the polymer solution at about 2.37 eV. The intersection theory and the voltammetry methods corroborate the experiment and the discussion of the results obtained.

Redox activity of nickel and vanadium porphyrins: a possible mechanism behind petroleum genesis and maturation?

The presence of metalloporphyrins in crude oil has been known for many years. In contrast, their role on the physical-chemical properties is only now beginning to be understood. In this study, we test using high-level ab initio calculations, the hypothesis of a possible redox catalytic activity of vanadium and nickel metalloporphyrins in crude oil, illustrated by the oxidation of methanol to formaldehyde and hydrogen dissociation, respectively. This process which may take place during petroleum genesis and maturation, explains some of its physical-chemical properties, such as polar chains, the absence of alcohols, the trapping of porphyrins within macromolecular aggregates.

Discerning Inter- and Intramolecular Vibrations of Sulfur Polyaromatic Compounds

Thiophenes are an important class of molecules in fields as diverse as petrochemistry, molecular electronics, and optoelectronics. Thiophenic submolecular motifs are thought to play a role in molecular association and nanoaggregation phenomena in both pure materials and natural and synthetic mixtures. Vibrational (infrared and Raman) spectroscopy provides the means to characterize these species. In this work far-infrared photoacoustic and low-frequency Raman spectra of a series of polycyclic aromatic hydrocarbons containing sulfur have been measured and interpreted using DFT calculations based on a perturbational-variational method coupled with potential truncation. The approach and outcomes illustrate how inter- and intramolecular vibrations for thiophenic systems in single and multicomponent mixtures can be discriminated. This work offers the perspective to search the inter- and intramolecular signatures of the main submolecular motifs and heteroelements postulated as being present in the asphaltenes.

Graphene-based acceptor molecules for organic photovoltaic cells: a predictive study identifying high modularity and morphological stability

An idealized donor:acceptor pair is proposed for improved organic photovoltaic lifetimes and efficiencies.

1/f ruffle oscillations in plasma membranes of amphibian epithelial cells under normal and inverted gravitational orientations

Membrane ruffle fluctuations of amphibian epithelial cells A6 (CCL102) cultured in normal and upside down oriented plates have been analyzed through video microscopy. Our results reveal that their edge ruffle fluctuations exhibit a stochastic dynamics with 1/f(alpha) power spectrum over at least two decades at low frequencies and long range correlated, self-affine lateral border profiles. In a few and small areas of the membrane, probably nearby focal contacts, we found periodic oscillations which could be induced by myosin driven contraction of stress fibers. Furthermore, whereas the different gravitational orientations had none or little effect on the structure (power spectra and surface roughness) of these membrane ruffle fluctuations, their dynamic parameters were differentially affected. Indeed, the decay time of ruffles remained unchanged, but the period of lamellipodia oscillations near the focal adhesion points was significantly altered in A6 cells cultured upside down.

On a Simple Nonisothermal Adsorption Experiment with Organic Vapors and an Inertial Microbalance To Study the Surface Properties of Hybrid (Organic/Inorganic) Porous Materials

A nonisothermal adsorption experiment using a controlled flow of cyclopentane in the 333-313 K range is used to simultaneously estimate the specific surface area and micropore volume of a hybrid (organic/inorganic) alcogel. For reference, the method is also applied to an all-inorganic material with a more rigid structure, namely, a high surface area SiO(2)-Al(2)O(3). The proposed data analysis provides guidelines to determine whether adsorption data on a certain adsorbate/adsorbent system can be modeled effectively as a convolution of BET (meso- and macropore) and Dubinin-Radushkevitch (DR, micropore) contributions. Copyright 2000 Academic Press.

Circadian pattern of cercarial emergence in Schistosoma mansoni (Platyhelminthes:Digenea) from isolated Biomphalaria glabrata

The present work aimed to compare the acrophases (peak hours) of emergence of Schistosoma mansoni cercariae among isolated individuals of the snail Biomphalaria glabrata. Laboratory stocks of melanic B. glabrata from the same biotope as the S. mansoni strain (Belo Horizonte, Minas Gerais) were used. Twenty-two snails individually exposed to five miracidia were tested. Chronobiological trials were performed outdoors after an acclimation period of at least a week. Three groups of snails were tested between November 1989 and April 1991. Cercarial emergence from individual isolated snails was quantified every 3 h for 3 consecutive days. In all trials, most cercariae were found to emerge during daytime (94.9%). Time series and chronograms showed recurrent peaks during the daytime. The periodogram suggested that 24 h was the period that best fitted cercarial emergence data in 90.9% of the snails. The single cosinor analysis confirmed 24-h rhythms in 95.5% of the snails. Acrophases of cercarial emergence among individual snails occurred between 14:15 and 17:02. They did not differ significantly. The population cosinor analysis indicated greater homogeneity in the 24-h rhythms of cercarial emergence than in the snail groups of each chronobiological trial. Acrophases of cercarial emergence occurred between 14:53 and 15:27 and did not differ significantly among all trials. Data from the three trials were pooled and analyzed using the population cosinor. This statistical method indicated a homogeneity in the 24-h rhythms of cercarial. emergence from all snails, with acrophase occurring around 15:00. Results showed that the acrophases of cercarial emergence of S. mansoni are similar among isolated B. glabrata specimens. Data support the hypothesis of a "gate" rhythm in the dynamics of cercarial production and emergence. It is suggested that the adaptive importance of the "gate" mechanism is associated with the concentration of cercariae in the water at times when the vertebrate is present, optimizing the contact between the parasite and the host. The emergence of some cercariae at night (5.1% of the total number of emerged cercariae) suggests a flexible "gate" that could be associated with a residual light effect or with experimental procedures in the laboratory.