The donor-acceptor copolymer containing benzothiadiazole (electron acceptor), linked to functionalized fluorene (electron donor), [poly[9,9-bis(3'-(tert-butyl propanoate))fluorene-co-4,7-(2,1,3-benzothiadiazole)] (LaPPS40), was synthesized through the Suzuki route. The polymer was characterized by scanning electron microscopy, gel permeation chromatography, NMR, thermal analysis, cyclic voltammetry, X-ray photoelectron spectroscopy, UV-vis spectrometry, and photophysical measurements. Theoretical calculations (density functional theory and semiempirical methodologies) used to simulate the geometry of some oligomers and the dipole moments of molecular orbitals involved were in excellent agreement with experimental results. Using such data, the higher energy absorption band was attributed to the π-π* (S(0) → S(4)) transition of the fluorene units and the lower lying band was attributed to the intramolecular (ICT) (S(0) → S(1)) charge transfer between acceptor (benzothiadiazole) and donor groups (fluorene) (D-A structure). The ICT character of this band was confirmed by its solvatochromic properties using solvents with different dielectric properties, and this behavior could be well described by the Lippert-Mataga equation. To explain the solvatochromic behavior, both the magnitude and orientation of the dipole moments in the electronic ground state and in the excited state were analyzed using the theoretical data. According to these data, the change in magnitude of the dipole moments was very small for both transitions but the spatial orientation changed remarkably for the lower energy band ascribed to the ICT band.
The in vitro antioxidant properties of golden grass (GG), a grass‐like herb (
Syngonanthus nitens
), were investigated by electron paramagnetic resonance (EPR) spectroscopy. We measured the antioxidant capacity of methanolic extracts based on their ability to scavenge 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical. The kinetics of reaction between DPPH and GG extract was determined. This kinetics followed a biexponential decay, and this behavior was attributed to different flavonoids acting together as antioxidants. Isoorientin and luteolin, which are two of the eight flavonoids found in GG extract, were used to investigate kinetics of reaction between DPPH and both the flavonoids acting separately and together. The antioxidant activity of GG extract was determined in terms of the vitamin C equivalent antioxidant capacity (VCEAC). Compared to other well‐known plant‐based antioxidants, such as pulp and peels of fruit and vegetables,
S. nitens
presented a high antioxidant capacity (VCEAC = 1,485 ± 198 mg/100 g), indicating that it should be regarded as a valuable source of antioxidants and also that it may bestow health benefits when consumed.
Background:
In the last 40 years, scientific efforts were focused on the efficiency improvement
in organic photovoltaic devices. Bleaching agents were used to absorb UV light and
convert it into lower energy radiation appear as potential candidates for further improvements. The
present contribution investigated the effect of adding umbelliferone to poly(3,4-ethylenedioxythiophene)
polystyrene sulfonate (PEDOT:PSS) on its optical and electrical properties.
Methods:
Characterizations were performed under various umbelliferone concentrations. Fluorescence
decay lifetimes were obtained using a MicroTime 200 system (PicoQuant). The UV–vis absorption
spectra were obtained with a GE Healthcare Ultrospec 2100 pro Spectrometer. The electrical
conductivity measurements as a function of temperature using a cryostat model ARS
CS202AE-DMX-1AL.
Results:
The absorbance increases around 325 nm and decreases in the near infrared s the umbelliferone
concentration is increased. It also decreases the absorption in the visible spectrum, concomitantly
with a significant increase in the UV region. The electrical conductivity for the umbelliferone
doped PEDOT:PSS films display an increase with increasing temperature, but does not follow
a linear behavior with the increase of umbelliferone concentration in the films.
Conclusion:
It was shown that the absorbance displays a redshift in doped samples, while photoluminescence
experiments demonstrated that UV light is converted to the visible spectrum more
efficiently, which is a desirable feature for photovoltaic devices. Also, the electrical conductivity of
PEDOT:PSS is increased for moderate umbelliferone concentrations.
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