Effect of fluorine on the photovoltaic properties of 2,1,3-benzothiadiazole-based alternating conjugated polymers by changing the position and number of fluorine atoms.

Fluorination is one of the most effective ways to manipulate molecular packing, optical bandgap and molecular energy levels in organic semiconductor materials. In this work, different number of fluorine atoms was introduced into the acceptor moiety 2,2'-dithiophene linked 2,1,3-benzothiadiazole, utilizing the alkylthiophene modified dithieno[2,3-d:2',3'-d']benzo[1,2-b:4,5-b] (DTBDT) as the donor unit, three polymers: PDTBDT-0F-BTs, PDTBDT-2F-BTs and PDTBDT-6F-FBTs were synthesized. With the number of fluorine atoms in each repeat unit of polymers varying from 0 to 2 and then up to 6, PDTBDT-0F-BTs, PDTBDT-2F-BTs and PDTBDT-6F-FBTs exhibited gradually downshifted energy levels and improved dielectric constants (εr) from 3.4 to 4.3 to 5.8, further successively increased charge transport mobilities. As a result, the power conversion efficiency (PCE) of the bulk heterojunction organic photovoltaic devices (BHJ-OPV) from the blend films of aforementioned polymers paired with PC71BM were gradually increased from 1.69 for PDTBDT-0F-BTs to 1.89 for PDTBDT-2F-BTs and then to 5.28 for PDTBDT-6F-FBTs. The results show that the continuous insertion of fluorine atoms into the repeating units of the benzothiadiazole conjugated polymer leads to the deepening of HOMO energy level, the increase of εr and the increase of charge mobility, which improve the efficiency of charge transfer and electron collection, thus improving the photovoltaic performance of BHJ-OPV.

A Nitroxide Radical Conjugated Polymer as an Additive to Reduce Nonradiative Energy Loss in Organic Solar Cells.

Nonfullerene-acceptor-based organic solar cells (NFA-OSCs) are now set off to the 20% power conversion efficiency milestone. To achieve this, minimizing all loss channels, including nonradiative photovoltage losses, seems a necessity. Nonradiative recombination, to a great extent, is known to be an inherent material property due to vibrationally induced decay of charge-transfer (CT) states or their back electron transfer to the triplet excitons. Herein, it is shown that the use of a new conjugated nitroxide radical polymer with 2,2,6,6-tetramethyl piperidine-1-oxyl side groups (GDTA) as an additive results in an improvement of the photovoltaic performance of NFA-OSCs based on different active layer materials. Upon the addition of GDTA, the open-circuit voltage (VOC ), fill factor (FF), and short-circuit current density (JSC ) improve simultaneously. This approach is applied to several material systems including state-of-the-art donor/acceptor pairs showing improvement from 15.8% to 17.6% (in the case of PM6:Y6) and from 17.5% to 18.3% (for PM6:BTP-eC9). Then, the possible reasons behind the observed improvements are discussed. The results point toward the suppression of the CT state to triplet excitons loss channel. This work presents a facile, promising, and generic approach to further improve the performance of NFA-OSCs.

[Study on the determination of permanganate index by UV-Vis spectrometry].

Permanganate index is an important parameter to evaluate the organic pollution for water sources, and the current national standard method is titration analysis which needs large sample and is complicated. A new analytical method of measuring permanganate index in surface water using UV-Vis spectrometry has thus been studied. In the laboratory work, analytical wave-length of UV-Vis spectrometry was chosen. The effect of sulfuric acid dosage, concentration and dosage of KMnO4 together with heating temperature and time was identified. In order to evaluate this new method, the linear relationship of this method was tested and the analysis results were compared with those by titration method. The selected optimum analysis parameters were: 525 nm wavelength, 25% H2SO4 dosage of 5.00 mL, 0.012 50 mol x L(-1) KMnO4 dosage of 2.00 mL, 30 min heating time at the temperature of 100 degrees C. This UV-Vis spectrometry method was successfully applied to measuring the permanganate index of the samples collected from the Jialing River and the Yangtze River. Compared with the current national standard method, this method is time and cost efficient, sensitive and precise, with low reagent usage; and is also easy to be manipulated and can be employed for online monitor, thus making it an environmental friendly analysing method.

Study on synthesis, crystal structure, antioxidant and DNA-binding of mono-, di- and poly-nuclear lanthanides complexes with bis(N-salicylidene)-3-oxapentane-1,5-diamine.

A Schiff base ligand bis(N-salicylidene)-3-oxapentane-1,5-diamine H2L have been prepared. Reaction of the shape-specific designed ligand with Ln(NO3)3⋅6H2O afforded three novel complexes, namely, Sm(L)(NO3)(DMF)(H2O) 1, [Eu(H2L)2(NO3)3]n2 and Tb2(L)2(NO3)23. The ligand and complexes were characterized by elemental analysis, UV-Vis, IR, NMR spectroscopy and X-ray crystallography. It is noteworthy that the complexes demonstrate three different types of the structure which changed according to the charge density and acidity of the lanthanide. Complex 1 is a discrete mononuclear species that Sm(III) ion is nine-coordinated in the structure and forming a distorted tricapped trigonal prism geometry. Complex 2 is possessed a 1-D ribbon framework constructed from an extended array of ten-coordinated Eu(3+) centers and the Schiff base ligands. Complex 3 is revealed as a centrosymmetric binuclear neutral entity, in which Tb(III) ion is eight-coordinated with the coordination surround of distorted square antiprism geometry. In order to explore the relationship between the structure and biological properties, the DNA-binding properties have been investigated by electronic absorption, fluorescence, and viscosity measurements. The results suggest that the ligand and complexes bind to DNA via groove modes. The intrinsic binding constants Kb of the complexes 1-3 are (1.19±0.112)×10(5), (4.22±0.086)×10(4) and (3.89±0.104)×10(4) M(-)(1) respectively. Moreover, the antioxidant activity experiments show that these compounds also exhibit good antioxidant activities against OH· and O2(-·) in vitro studies.

The V-shaped ligand bis(N-allylbenzimidazol-2-ylmethyl)benzylamine and its Ag(I) complex: synthesis, crystal structure, DNA-binding properties and antioxidation.

A novel dinuclear Ag(I) complex of the type, [Ag2L2](pic)2, was synthesized by the reaction of the V-shaped ligand bis(N-allylbenzimidazol-2-ylmethyl)benzylamine (L) with Ag(pic) (pic=picrate). Ligand L and Ag(I) complex were characterized on the basis of elemental analysis, UV-vis, IR, NMR spectroscopy and X-ray crystallography. Single-crystal X-ray revealed that two L coordinated to a central silver(I) cation in a near-linear fashion through their benzimidazol-1-yl nitrogen atoms, and a centrosymmetric dinuclear pore canal structure was constructed in the discrete [Ag2L(2)2](2+) cation. The DNA-binding properties of the free ligand L and Ag(I) complex have been carried out by using electronic absorption, fluorescence, and viscosity measurements. The results support that ligand L and Ag(I) complex both bind to DNA via an intercalative binding mode, and the affinity for DNA is more strongly in case of Ag(I) complex when compared with ligand L. Moreover, Ag(I) complex also exhibited potential antioxidant properties in vitro studies.