The theory of thermally activated delayed fluorescence for organic light emitting diodes.

The interest in organic molecules exhibiting thermally activated delayed fluorescence (TADF) has been reinvigorated in recent years owing to their potential to be exploited as emitters in highly efficient purely organic light emitting diodes (OLEDs). However, designing new molecules that exhibit efficient TADF is a non-trivial task because they would appear to require the optimisation of a number of contrasting properties. For example these molecules must exhibit rapid conversion between the singlet and triplet manifolds without the use of heavy elements to enhance spin-orbit coupling. They should also display a large fluorescence rate, but simultaneously a small energy gap between low lying singlet and triplet states. Consequently to achieve systematic material design, a detailed understanding of the fundamental factors influencing the photophysical behaviour of TADF emitters is essential. Towards achieving this goal, theory and computation is playing a crucial role. In this feature article the recent progress in the theory of organic TADF molecules in the context of OLEDs is presented, with a view of achieving a deeper understanding of these molecules and driving systematic material design.

Effects of omega-3 on metabolic markers in postmenopausal women with metabolic syndrome.

OBJECTIVE: The aim of this study was to evaluate the effect of diet alone or combined with omega-3 supplementation on metabolic and inflammatory markers in postmenopausal women with metabolic syndrome. METHODS: This randomized, controlled trial included 87 Brazilian women (age ≥ 45 years and with amenorrhea ≥ 12 months). Exclusion criteria were: cardiovascular disease, insulin-dependent diabetes, cancer, autoimmune diseases and use of either statins or hormone therapy. Participants were randomized to diet alone (n = 43, control) or diet plus omega-3 supplementation, 900 mg/day orally (n = 44). All women were provided with an individualized dietary prescription. Clinical, anthropometrical (body mass index and waist circumference) and biochemical variables were measured. The inflammatory profile included C-reactive protein, tumor necrosis factor α and interleukins (IL-1ß and IL-6). The intervention time was 6 months, with assessments at initiation and completion. Data were analyzed according to intention-to-treat, using the independent t-test and ANOVA. RESULTS: There were significant reductions in body mass index and waist circumference in both groups (p < 0.05) without significant changes in body fat or muscle mass. Intervention with diet plus omega-3 was associated with significant reduction in systolic (< 12.2%) and diastolic (< 8.2%) blood pressure, serum triglyceride concentration (< 21.4%), and insulin resistance (< 13.1%) (p < 0.05), as well as a reduction in serum IL-6 concentration (< 28.5%) (p = 0.034). CONCLUSION: In postmenopausal women with metabolic syndrome, dietary intervention plus supplementation of omega-3 resulted in a further decrease in triglycerides and blood pressure and also in an improvement in insulin resistance and inflammatory markers, important components of metabolic syndrome.

Características de carcaça de cabritos criados em dois sistemas de terminação / Carcass characteristics of goat kids in two finishing systems

Avaliaram-se as características da carcaça de cabritos Saanen confinados, Saanen e 7/8 Boer - 1/8 Saanen semiconfinados, bem como a influência de grupo genético e sistema de terminação sobre o rendimento comercial, índice de compacidade, não constituintes, área de olho de lombo, força de cisalhamento, gordura, teor de umidade e teor de extrato etéreo. Utilizaram-se 31 machos inteiros, com aproximadamente 128 dias de idade e 22,9±2,4kg de peso vivo. Destes, 22 eram da raça Saanen e nove animais eram mestiços 7/8 Boer - 1/8 Saanen. Os animais da raça Saanen foram divididos em dois grupos de 11 animais, sendo um grupo mantido em confinamento e outro em semiconfinamento, enquanto os mestiços foram mantidos em semiconfinamento. Compararam-se os sistemas de terminação na raça Saanen, e os grupos genéticos no sistema semiconfinado. Os animais confinados receberam 3,5% do PV em ração completa peletizada; os semiconfinados tiveram acesso à pastagem e suplementação de 1,5% do PV em ração concentrada peletizada. Aos 47 dias de terminação, os animais foram abatidos e as características de carcaça determinadas por meio de uma amostra de lombo dissecado. Foram observadas diferenças entre sistemas de terminação para rendimento comercial de carcaça, índice de compacidade da carcaça, não constituintes de carcaça, área de olho de lombo, força de cisalhamento, gordura, teor de umidade e de extrato etéreo. Entre os grupos genéticos, foram observadas diferenças para área de olho de lombo, espessura de gordura e matéria mineral. O sistema de terminação exerceu influência sobre as características de carcaça avaliadas. A raça Saanen pode ser utilizada para a produção de carne quando submetida ao confinamento.

Was evaluated carcass characteristics of feedlot goats Saanen, Saanen and 7/8 Boer - 1/8 Saanen semi-confined, as well as the influence of the genetic groups and finishing systems on the commercial performance, compactness index, not constituents, area ribeye, shear force, fat, moisture and ether extract content. Were used 31 bulls, with approximately 128 days of age and 22.9±2.4kg live weight (LW). Of these, 22 were Saanen, and nine animals were crossbred 7/8 Boer - 1/8 Saanen. The Saanen animals were divided into two groups of 11 animals each, one group and another kept in a feedlot in semiconfinement, while crossbreds were kept in semiconfinement. Was compared the finishing systems in Saanen, and genetic groups in semi-confined system. The confined animals received 3.5% of LW in complete pelleted ration, the semiconfinados had access to pasture and supplementation of 1.5% of LW in pelleted concentrate ration. At 47 days of terminating the animals were slaughtered and the carcass characteristics determined using a sample loin dissected. Differences were observed between finishing systems for commercial carcass yield, carcass compactness index, not constituents carcass, loin eye area, shear force, fat, moisture and ether extract. Between genetic groups, differences were observed for ribeye area, fat thickness and mineral matter. The finishing system exerted influence on carcass traits evaluated. The Saanen can be used for the production of meat when subjected to confinement.

Interfacial exciplex formation in bilayers of conjugated polymers.

The donor-acceptor interactions in sequential bilayer and blend films are investigated. Steady-state and time-resolved photoluminescence (PL) were measured to characterize the samples at different geometries of photoluminescence collection. At standard excitation, with the laser incidence at 45° of the normal direction of the sample surface, a band related to the aggregate states of donor molecules appears for both blend and bilayer at around 540 nm. For the PL spectra acquired from the edge of the bilayer, with the laser incidence made at normal direction of the sample surface (90° geometry), a new featureless band emission, red-shifted from donor and acceptor emission regions was observed and assigned as the emission from interfacial exciplex states. The conformational complexity coming from donor/acceptor interactions at the heterojunction interface of the bilayer is at the origin of this interfacial exciplex emission.

Measurement of interchain and intrachain exciton hopping barriers in luminescent polymer.

The integrated photoluminescence intensity in thin films of 'Super Yellow' copolymer has been analyzed using a Mott-like temperature dependence. This has enabled us to observe contributions from two emission channels, indicative of exciton recombination proceeding from two distinct origins. At high temperature, interchain thermally activated exciton energy transfer and migration dominates, resulting in large scale quenching of the integrated emission intensity and hence the photoluminescence quantum yield. However, at relatively low temperature, an additional increase of the integrated emission intensity occurs. This new channel of emission has been attributed to recombination from excitons where intrachain exciton energy transfer between adjacent subunits of the copolymer backbone becomes hindered. The activation energy barriers that control both of these emission channels have been obtained and are correlated with chain backbone degrees of freedom.

Long range energy transfer in conjugated polymer sequential bilayers.

Steady-state and time-resolved photoluminescence have been used to investigate the optical properties of bilayer and blend films made from poly(9,9-dioctyl-fluorene-2,7-diyl) (PFO) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH PPV). Energy transfer has been observed in both systems. From steady-state photoluminescence measurements, the energy transfer was characterized by the effective enhancement of the MEH PPV emission intensity after exciting the donor states. Relatively faster decays for the PFO donor emission have been observed in the blends as well as in the bilayer structures, confirming effective energy transfer in both structures. In contrast to the bilayers, the time decay of the acceptor emission in the blends presents a long decay component, which was assigned to the exciplex formation in these samples. For the blends the acceptor emission is in fact a composition of exciplex and MEH PPV emissions, the later being due to Förster energy transfer from PFO. In the bilayers, the exciplex is not observed and temperature dependence photoluminescence measurements show that exciton migration has no significant contribution to the energy transfer. The efficiency and very long range of the energy transfer in the bilayers is explained assuming a surface-surface interaction geometry where the donor/acceptor distances involved are much longer than the common Förster radius.

Enhanced triplet formation by twisted intramolecular charge-transfer excited states in conjugated oligomers and polymers.

The triplet yield and intersystem crossing rate of a set of conjugated oligomers and polymers that, in polar solvents, form a charge-transfer state with a twisted conformation has been investigated. It was observed that in these dibenzothiophene-fluorene oligomers a greater than 10-fold increase on the triplet yield is achieved by simply changing the medium polarity to favor the formation of the twisted charge-transfer state, while the fluorescence lifetime is only slightly increased. The increase in the intersystem crossing rate is attributed to the improved mixing between the singlet and triplet states in the twisted excited state. In analogous polymers, the intersystem crossing rate does not show the same increase, most likely because of the greater energetic and conformational disorder increasing the intersystem crossing rate at all times, regardless of the formation of the twisted charge-transfer state or not.

Photophysical studies of alpha,omega-dicyano-oligothiophenes NC(C4H2S)nCN (n = 1-6).

The photophysics of six oligothiophenes end-capped with cyano groups (CNalphan) was investigated in solution at room and low temperature. The study comprises singlet-singlet and triplet-triplet absorption and emission spectra together with lifetimes and quantum yields for all the radiative and nonradiative processes. From the lifetimes and quantum yields, it was possible to extract the rate constants for all the processes. Singlet oxygen yields were also determined, revealing an efficient sensitization (SDelta approximately 1) of its formation by the triplet state of the CNalphan. The introduction of the cyano groups is found to decrease the energetic separation between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, leading to a red shift of the absorption and the emission when compared with the unsubstituted counterparts, the alpha-oligothiophenes. Phosphorescence is only observed for the first member of the series, CNalpha1.